Nouveau - Jan 2024 - [PATCH] mm: Remove double faults once write a device pfn

Am 22.01.24 um 04:32 schrieb Xianrong Zhou:
> The vmf_insert_pfn_prot could cause unnecessary double faults
> on a device pfn. Because currently the vmf_insert_pfn_prot does
> not make the pfn writable so the pte entry is normally read-only
> or dirty catching.
What? How do you got to this conclusion?
> The first fault only sets up the pte entry which actually is
> dirty catching. And the second immediate fault to the pfn due
> to first dirty catching when the cpu re-execute the store
> instruction.
It could be that this is done to work around some hw behavior, but not 
because of dirty catching.
> Normally if the drivers call vmf_insert_pfn_prot and also supply
> 'pfn_mkwrite' callback within vm_operations_struct which requires
> the pte to be dirty catching then the vmf_insert_pfn_prot and the
> double fault are reasonable. It is not a problem.
Well, as far as I can see that behavior absolutely doesn't make sense.

When pfn_mkwrite is requested then the driver should use PAGE_COPY, 
which is exactly what VMWGFX (the only driver using dirty tracking) is 
doing.

Everybody else uses PAGE_SHARED which should make the pte writeable 
immediately.

Regards,
Christian.
>
> However the most of drivers calling vmf_insert_pfn_prot do not
> supply the 'pfn_mkwrite' callback so that the second fault is
> unnecessary.
>
> So just like vmf_insert_mixed and vmf_insert_mixed_mkwrite pair,
> we should also supply vmf_insert_pfn_mkwrite for drivers as well.
>
> Signed-off-by: Xianrong Zhou <Xianrong.Zhou at amd.com>
> ---
>   arch/x86/entry/vdso/vma.c                  |  3 ++-
>   drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c    |  2 +-
>   drivers/gpu/drm/i915/gem/i915_gem_ttm.c    |  2 +-
>   drivers/gpu/drm/nouveau/nouveau_gem.c      |  2 +-
>   drivers/gpu/drm/radeon/radeon_gem.c        |  2 +-
>   drivers/gpu/drm/ttm/ttm_bo_vm.c            |  8 +++++---
>   drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c |  8 +++++---
>   include/drm/ttm/ttm_bo.h                   |  3 ++-
>   include/linux/mm.h                         |  2 +-
>   mm/memory.c                                | 14 +++++++++++---
>   10 files changed, 30 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
> index 7645730dc228..dd2431c2975f 100644
> --- a/arch/x86/entry/vdso/vma.c
> +++ b/arch/x86/entry/vdso/vma.c
> @@ -185,7 +185,8 @@ static vm_fault_t vvar_fault(const struct
vm_special_mapping *sm,
>   		if (pvti && vclock_was_used(VDSO_CLOCKMODE_PVCLOCK)) {
>   			return vmf_insert_pfn_prot(vma, vmf->address,
>   					__pa(pvti) >> PAGE_SHIFT,
> -					pgprot_decrypted(vma->vm_page_prot));
> +					pgprot_decrypted(vma->vm_page_prot),
> +					true);
>   		}
>   	} else if (sym_offset == image->sym_hvclock_page) {
>   		pfn = hv_get_tsc_pfn();
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> index 49a5f1c73b3e..adcb20d9e624 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> @@ -64,7 +64,7 @@ static vm_fault_t amdgpu_gem_fault(struct vm_fault *vmf)
>   		}
>   
>   		ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma->vm_page_prot,
> -					       TTM_BO_VM_NUM_PREFAULT);
> +					       TTM_BO_VM_NUM_PREFAULT, true);
>   
>   		drm_dev_exit(idx);
>   	} else {
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> index 9227f8146a58..c6f13ae6c308 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> @@ -1114,7 +1114,7 @@ static vm_fault_t vm_fault_ttm(struct vm_fault *vmf)
>   
>   	if (drm_dev_enter(dev, &idx)) {
>   		ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma->vm_page_prot,
> -					       TTM_BO_VM_NUM_PREFAULT);
> +					       TTM_BO_VM_NUM_PREFAULT, true);
>   		drm_dev_exit(idx);
>   	} else {
>   		ret = ttm_bo_vm_dummy_page(vmf, vmf->vma->vm_page_prot);
> diff --git a/drivers/gpu/drm/nouveau/nouveau_gem.c
b/drivers/gpu/drm/nouveau/nouveau_gem.c
> index 49c2bcbef129..7e1453762ec9 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_gem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
> @@ -56,7 +56,7 @@ static vm_fault_t nouveau_ttm_fault(struct vm_fault *vmf)
>   
>   	nouveau_bo_del_io_reserve_lru(bo);
>   	prot = vm_get_page_prot(vma->vm_flags);
> -	ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT);
> +	ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT, true);
>   	nouveau_bo_add_io_reserve_lru(bo);
>   	if (ret == VM_FAULT_RETRY && !(vmf->flags &
FAULT_FLAG_RETRY_NOWAIT))
>   		return ret;
> diff --git a/drivers/gpu/drm/radeon/radeon_gem.c
b/drivers/gpu/drm/radeon/radeon_gem.c
> index 3fec3acdaf28..b21cf00ae162 100644
> --- a/drivers/gpu/drm/radeon/radeon_gem.c
> +++ b/drivers/gpu/drm/radeon/radeon_gem.c
> @@ -62,7 +62,7 @@ static vm_fault_t radeon_gem_fault(struct vm_fault *vmf)
>   		goto unlock_resv;
>   
>   	ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma->vm_page_prot,
> -				       TTM_BO_VM_NUM_PREFAULT);
> +				       TTM_BO_VM_NUM_PREFAULT, true);
>   	if (ret == VM_FAULT_RETRY && !(vmf->flags &
FAULT_FLAG_RETRY_NOWAIT))
>   		goto unlock_mclk;
>   
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c
b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index 4212b8c91dd4..7d14a7d267aa 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> @@ -167,6 +167,7 @@ EXPORT_SYMBOL(ttm_bo_vm_reserve);
>    * @num_prefault: Maximum number of prefault pages. The caller may want
to
>    * specify this based on madvice settings and the size of the GPU object
>    * backed by the memory.
> + * @mkwrite: make the pfn or page writable
>    *
>    * This function inserts one or more page table entries pointing to the
>    * memory backing the buffer object, and then returns a return code
> @@ -180,7 +181,8 @@ EXPORT_SYMBOL(ttm_bo_vm_reserve);
>    */
>   vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
>   				    pgprot_t prot,
> -				    pgoff_t num_prefault)
> +				    pgoff_t num_prefault,
> +				    bool mkwrite)
>   {
>   	struct vm_area_struct *vma = vmf->vma;
>   	struct ttm_buffer_object *bo = vma->vm_private_data;
> @@ -263,7 +265,7 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault
*vmf,
>   		 * at arbitrary times while the data is mmap'ed.
>   		 * See vmf_insert_pfn_prot() for a discussion.
>   		 */
> -		ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
> +		ret = vmf_insert_pfn_prot(vma, address, pfn, prot, mkwrite);
>   
>   		/* Never error on prefaulted PTEs */
>   		if (unlikely((ret & VM_FAULT_ERROR))) {
> @@ -312,7 +314,7 @@ vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf,
pgprot_t prot)
>   	/* Prefault the entire VMA range right away to avoid further faults */
>   	for (address = vma->vm_start; address < vma->vm_end;
>   	     address += PAGE_SIZE)
> -		ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
> +		ret = vmf_insert_pfn_prot(vma, address, pfn, prot, true);
>   
>   	return ret;
>   }
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
> index 74ff2812d66a..bb8e4b641681 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
> @@ -452,12 +452,14 @@ vm_fault_t vmw_bo_vm_fault(struct vm_fault *vmf)
>   	 * sure the page protection is write-enabled so we don't get
>   	 * a lot of unnecessary write faults.
>   	 */
> -	if (vbo->dirty && vbo->dirty->method ==
VMW_BO_DIRTY_MKWRITE)
> +	if (vbo->dirty && vbo->dirty->method ==
VMW_BO_DIRTY_MKWRITE) {
>   		prot = vm_get_page_prot(vma->vm_flags & ~VM_SHARED);
> -	else
> +		ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault, false);
> +	} else {
>   		prot = vm_get_page_prot(vma->vm_flags);
> +		ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault, true);
> +	}
>   
> -	ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault);
>   	if (ret == VM_FAULT_RETRY && !(vmf->flags &
FAULT_FLAG_RETRY_NOWAIT))
>   		return ret;
>   
> diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
> index 0223a41a64b2..66e293db69ee 100644
> --- a/include/drm/ttm/ttm_bo.h
> +++ b/include/drm/ttm/ttm_bo.h
> @@ -386,7 +386,8 @@ vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object
*bo,
>   			     struct vm_fault *vmf);
>   vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
>   				    pgprot_t prot,
> -				    pgoff_t num_prefault);
> +				    pgoff_t num_prefault,
> +				    bool mkwrite);
>   vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf);
>   void ttm_bo_vm_open(struct vm_area_struct *vma);
>   void ttm_bo_vm_close(struct vm_area_struct *vma);
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index f5a97dec5169..f8868e28ea04 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3553,7 +3553,7 @@ int vm_map_pages_zero(struct vm_area_struct *vma,
struct page **pages,
>   vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
>   			unsigned long pfn);
>   vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long
addr,
> -			unsigned long pfn, pgprot_t pgprot);
> +			unsigned long pfn, pgprot_t pgprot, bool mkwrite);
>   vm_fault_t vmf_insert_mixed(struct vm_area_struct *vma, unsigned long
addr,
>   			pfn_t pfn);
>   vm_fault_t vmf_insert_mixed_mkwrite(struct vm_area_struct *vma,
> diff --git a/mm/memory.c b/mm/memory.c
> index 7e1f4849463a..2c28f1a349ff 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2195,6 +2195,7 @@ static vm_fault_t insert_pfn(struct vm_area_struct
*vma, unsigned long addr,
>    * @addr: target user address of this page
>    * @pfn: source kernel pfn
>    * @pgprot: pgprot flags for the inserted page
> + * @mkwrite: make the pfn writable
>    *
>    * This is exactly like vmf_insert_pfn(), except that it allows drivers
>    * to override pgprot on a per-page basis.
> @@ -2223,7 +2224,7 @@ static vm_fault_t insert_pfn(struct vm_area_struct
*vma, unsigned long addr,
>    * Return: vm_fault_t value.
>    */
>   vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long
addr,
> -			unsigned long pfn, pgprot_t pgprot)
> +			unsigned long pfn, pgprot_t pgprot, bool mkwrite)
>   {
>   	/*
>   	 * Technically, architectures with pte_special can avoid all these
> @@ -2246,7 +2247,7 @@ vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct
*vma, unsigned long addr,
>   	track_pfn_insert(vma, &pgprot, __pfn_to_pfn_t(pfn, PFN_DEV));
>   
>   	return insert_pfn(vma, addr, __pfn_to_pfn_t(pfn, PFN_DEV), pgprot,
> -			false);
> +			mkwrite);
>   }
>   EXPORT_SYMBOL(vmf_insert_pfn_prot);
>   
> @@ -2273,10 +2274,17 @@ EXPORT_SYMBOL(vmf_insert_pfn_prot);
>   vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
>   			unsigned long pfn)
>   {
> -	return vmf_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot);
> +	return vmf_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot, false);
>   }
>   EXPORT_SYMBOL(vmf_insert_pfn);
>   
> +vm_fault_t vmf_insert_pfn_mkwrite(struct vm_area_struct *vma, unsigned
long addr,
> +			unsigned long pfn)
> +{
> +	return vmf_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot, true);
> +}
> +EXPORT_SYMBOL(vmf_insert_pfn_mkwrite);
> +
>   static bool vm_mixed_ok(struct vm_area_struct *vma, pfn_t pfn)
>   {
>   	/* these checks mirror the abort conditions in vm_normal_page */

[AMD Official Use Only - General]
> > The vmf_insert_pfn_prot could cause unnecessary double faults on a
> > device pfn. Because currently the vmf_insert_pfn_prot does not make
> > the pfn writable so the pte entry is normally read-only or dirty
> > catching.
>
> What? How do you got to this conclusion?
Sorry. I did not mention that this problem only exists on arm64 platform.
Because on arm64 platform the PTE_RDONLY is automatically attached to
the userspace pte entries even through VM_WRITE + VM_SHARE.
The  PTE_RDONLY needs to be cleared in vmf_insert_pfn_prot. However
vmf_insert_pfn_prot do not make the pte writable passing false @mkwrite
to insert_pfn.
>
> > The first fault only sets up the pte entry which actually is dirty
> > catching. And the second immediate fault to the pfn due to first dirty
> > catching when the cpu re-execute the store instruction.
>
> It could be that this is done to work around some hw behavior, but not
> because of dirty catching.
>
> > Normally if the drivers call vmf_insert_pfn_prot and also supply
> > 'pfn_mkwrite' callback within vm_operations_struct which
requires the
> > pte to be dirty catching then the vmf_insert_pfn_prot and the double
> > fault are reasonable. It is not a problem.
>
> Well, as far as I can see that behavior absolutely doesn't make sense.
>
> When pfn_mkwrite is requested then the driver should use PAGE_COPY, which
> is exactly what VMWGFX (the only driver using dirty tracking) is doing.
>
> Everybody else uses PAGE_SHARED which should make the pte writeable
> immediately.
>
> Regards,
> Christian.
>
> >
> > However the most of drivers calling vmf_insert_pfn_prot do not supply
> > the 'pfn_mkwrite' callback so that the second fault is
unnecessary.
> >
> > So just like vmf_insert_mixed and vmf_insert_mixed_mkwrite pair, we
> > should also supply vmf_insert_pfn_mkwrite for drivers as well.
> >
> > Signed-off-by: Xianrong Zhou <Xianrong.Zhou at amd.com>
> > ---
> >   arch/x86/entry/vdso/vma.c                  |  3 ++-
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c    |  2 +-
> >   drivers/gpu/drm/i915/gem/i915_gem_ttm.c    |  2 +-
> >   drivers/gpu/drm/nouveau/nouveau_gem.c      |  2 +-
> >   drivers/gpu/drm/radeon/radeon_gem.c        |  2 +-
> >   drivers/gpu/drm/ttm/ttm_bo_vm.c            |  8 +++++---
> >   drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c |  8 +++++---
> >   include/drm/ttm/ttm_bo.h                   |  3 ++-
> >   include/linux/mm.h                         |  2 +-
> >   mm/memory.c                                | 14 +++++++++++---
> >   10 files changed, 30 insertions(+), 16 deletions(-)
> >
> > diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
> > index 7645730dc228..dd2431c2975f 100644
> > --- a/arch/x86/entry/vdso/vma.c
> > +++ b/arch/x86/entry/vdso/vma.c
> > @@ -185,7 +185,8 @@ static vm_fault_t vvar_fault(const struct
> vm_special_mapping *sm,
> >             if (pvti &&
vclock_was_used(VDSO_CLOCKMODE_PVCLOCK))
> {
> >                     return vmf_insert_pfn_prot(vma, vmf->address,
> >                                     __pa(pvti) >> PAGE_SHIFT,
> > -                                   pgprot_decrypted(vma-
> >vm_page_prot));
> > +                                   pgprot_decrypted(vma-
> >vm_page_prot),
> > +                                   true);
> >             }
> >     } else if (sym_offset == image->sym_hvclock_page) {
> >             pfn = hv_get_tsc_pfn();
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> > index 49a5f1c73b3e..adcb20d9e624 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> > @@ -64,7 +64,7 @@ static vm_fault_t amdgpu_gem_fault(struct vm_fault
> *vmf)
> >             }
> >
> >             ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma-
> >vm_page_prot,
> > -                                          TTM_BO_VM_NUM_PREFAULT);
> > +                                          TTM_BO_VM_NUM_PREFAULT,
> true);
> >
> >             drm_dev_exit(idx);
> >     } else {
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > index 9227f8146a58..c6f13ae6c308 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > @@ -1114,7 +1114,7 @@ static vm_fault_t vm_fault_ttm(struct vm_fault
> > *vmf)
> >
> >     if (drm_dev_enter(dev, &idx)) {
> >             ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma-
> >vm_page_prot,
> > -                                          TTM_BO_VM_NUM_PREFAULT);
> > +                                          TTM_BO_VM_NUM_PREFAULT,
> true);
> >             drm_dev_exit(idx);
> >     } else {
> >             ret = ttm_bo_vm_dummy_page(vmf, vmf->vma-
> >vm_page_prot); diff
> > --git a/drivers/gpu/drm/nouveau/nouveau_gem.c
> > b/drivers/gpu/drm/nouveau/nouveau_gem.c
> > index 49c2bcbef129..7e1453762ec9 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_gem.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
> > @@ -56,7 +56,7 @@ static vm_fault_t nouveau_ttm_fault(struct vm_fault
> > *vmf)
> >
> >     nouveau_bo_del_io_reserve_lru(bo);
> >     prot = vm_get_page_prot(vma->vm_flags);
> > -   ret = ttm_bo_vm_fault_reserved(vmf, prot,
> TTM_BO_VM_NUM_PREFAULT);
> > +   ret = ttm_bo_vm_fault_reserved(vmf, prot,
> TTM_BO_VM_NUM_PREFAULT,
> > +true);
> >     nouveau_bo_add_io_reserve_lru(bo);
> >     if (ret == VM_FAULT_RETRY && !(vmf->flags &
> FAULT_FLAG_RETRY_NOWAIT))
> >             return ret;
> > diff --git a/drivers/gpu/drm/radeon/radeon_gem.c
> > b/drivers/gpu/drm/radeon/radeon_gem.c
> > index 3fec3acdaf28..b21cf00ae162 100644
> > --- a/drivers/gpu/drm/radeon/radeon_gem.c
> > +++ b/drivers/gpu/drm/radeon/radeon_gem.c
> > @@ -62,7 +62,7 @@ static vm_fault_t radeon_gem_fault(struct vm_fault
> *vmf)
> >             goto unlock_resv;
> >
> >     ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma->vm_page_prot,
> > -                                  TTM_BO_VM_NUM_PREFAULT);
> > +                                  TTM_BO_VM_NUM_PREFAULT, true);
> >     if (ret == VM_FAULT_RETRY && !(vmf->flags &
> FAULT_FLAG_RETRY_NOWAIT))
> >             goto unlock_mclk;
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > b/drivers/gpu/drm/ttm/ttm_bo_vm.c index
> 4212b8c91dd4..7d14a7d267aa
> > 100644
> > --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > @@ -167,6 +167,7 @@ EXPORT_SYMBOL(ttm_bo_vm_reserve);
> >    * @num_prefault: Maximum number of prefault pages. The caller may
> want to
> >    * specify this based on madvice settings and the size of the GPU
object
> >    * backed by the memory.
> > + * @mkwrite: make the pfn or page writable
> >    *
> >    * This function inserts one or more page table entries pointing to
the
> >    * memory backing the buffer object, and then returns a return code
> > @@ -180,7 +181,8 @@ EXPORT_SYMBOL(ttm_bo_vm_reserve);
> >    */
> >   vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
> >                                 pgprot_t prot,
> > -                               pgoff_t num_prefault)
> > +                               pgoff_t num_prefault,
> > +                               bool mkwrite)
> >   {
> >     struct vm_area_struct *vma = vmf->vma;
> >     struct ttm_buffer_object *bo = vma->vm_private_data; @@ -263,7
> > +265,7 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
> >              * at arbitrary times while the data is mmap'ed.
> >              * See vmf_insert_pfn_prot() for a discussion.
> >              */
> > -           ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
> > +           ret = vmf_insert_pfn_prot(vma, address, pfn, prot,
mkwrite);
> >
> >             /* Never error on prefaulted PTEs */
> >             if (unlikely((ret & VM_FAULT_ERROR))) { @@ -312,7
+314,7
> @@
> > vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t prot)
> >     /* Prefault the entire VMA range right away to avoid further
faults */
> >     for (address = vma->vm_start; address < vma->vm_end;
> >          address += PAGE_SIZE)
> > -           ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
> > +           ret = vmf_insert_pfn_prot(vma, address, pfn, prot, true);
> >
> >     return ret;
> >   }
> > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
> > b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
> > index 74ff2812d66a..bb8e4b641681 100644
> > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
> > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
> > @@ -452,12 +452,14 @@ vm_fault_t vmw_bo_vm_fault(struct vm_fault
> *vmf)
> >      * sure the page protection is write-enabled so we don't get
> >      * a lot of unnecessary write faults.
> >      */
> > -   if (vbo->dirty && vbo->dirty->method ==
VMW_BO_DIRTY_MKWRITE)
> > +   if (vbo->dirty && vbo->dirty->method ==
VMW_BO_DIRTY_MKWRITE)
> {
> >             prot = vm_get_page_prot(vma->vm_flags &
~VM_SHARED);
> > -   else
> > +           ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault,
> false);
> > +   } else {
> >             prot = vm_get_page_prot(vma->vm_flags);
> > +           ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault,
> true);
> > +   }
> >
> > -   ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault);
> >     if (ret == VM_FAULT_RETRY && !(vmf->flags &
> FAULT_FLAG_RETRY_NOWAIT))
> >             return ret;
> >
> > diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h index
> > 0223a41a64b2..66e293db69ee 100644
> > --- a/include/drm/ttm/ttm_bo.h
> > +++ b/include/drm/ttm/ttm_bo.h
> > @@ -386,7 +386,8 @@ vm_fault_t ttm_bo_vm_reserve(struct
> ttm_buffer_object *bo,
> >                          struct vm_fault *vmf);
> >   vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
> >                                 pgprot_t prot,
> > -                               pgoff_t num_prefault);
> > +                               pgoff_t num_prefault,
> > +                               bool mkwrite);
> >   vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf);
> >   void ttm_bo_vm_open(struct vm_area_struct *vma);
> >   void ttm_bo_vm_close(struct vm_area_struct *vma); diff --git
> > a/include/linux/mm.h b/include/linux/mm.h index
> > f5a97dec5169..f8868e28ea04 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -3553,7 +3553,7 @@ int vm_map_pages_zero(struct vm_area_struct
> *vma, struct page **pages,
> >   vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long
> addr,
> >                     unsigned long pfn);
> >   vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned
> long addr,
> > -                   unsigned long pfn, pgprot_t pgprot);
> > +                   unsigned long pfn, pgprot_t pgprot, bool mkwrite);
> >   vm_fault_t vmf_insert_mixed(struct vm_area_struct *vma, unsigned
long
> addr,
> >                     pfn_t pfn);
> >   vm_fault_t vmf_insert_mixed_mkwrite(struct vm_area_struct *vma, diff
> > --git a/mm/memory.c b/mm/memory.c index 7e1f4849463a..2c28f1a349ff
> > 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -2195,6 +2195,7 @@ static vm_fault_t insert_pfn(struct
> vm_area_struct *vma, unsigned long addr,
> >    * @addr: target user address of this page
> >    * @pfn: source kernel pfn
> >    * @pgprot: pgprot flags for the inserted page
> > + * @mkwrite: make the pfn writable
> >    *
> >    * This is exactly like vmf_insert_pfn(), except that it allows
drivers
> >    * to override pgprot on a per-page basis.
> > @@ -2223,7 +2224,7 @@ static vm_fault_t insert_pfn(struct
> vm_area_struct *vma, unsigned long addr,
> >    * Return: vm_fault_t value.
> >    */
> >   vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned
> long addr,
> > -                   unsigned long pfn, pgprot_t pgprot)
> > +                   unsigned long pfn, pgprot_t pgprot, bool mkwrite)
> >   {
> >     /*
> >      * Technically, architectures with pte_special can avoid all these
> > @@ -2246,7 +2247,7 @@ vm_fault_t vmf_insert_pfn_prot(struct
> vm_area_struct *vma, unsigned long addr,
> >     track_pfn_insert(vma, &pgprot, __pfn_to_pfn_t(pfn, PFN_DEV));
> >
> >     return insert_pfn(vma, addr, __pfn_to_pfn_t(pfn, PFN_DEV), pgprot,
> > -                   false);
> > +                   mkwrite);
> >   }
> >   EXPORT_SYMBOL(vmf_insert_pfn_prot);
> >
> > @@ -2273,10 +2274,17 @@ EXPORT_SYMBOL(vmf_insert_pfn_prot);
> >   vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long
> addr,
> >                     unsigned long pfn)
> >   {
> > -   return vmf_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot);
> > +   return vmf_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot,
> > +false);
> >   }
> >   EXPORT_SYMBOL(vmf_insert_pfn);
> >
> > +vm_fault_t vmf_insert_pfn_mkwrite(struct vm_area_struct *vma,
unsigned
> long addr,
> > +                   unsigned long pfn)
> > +{
> > +   return vmf_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot,
> true);
> > +} EXPORT_SYMBOL(vmf_insert_pfn_mkwrite);
> > +
> >   static bool vm_mixed_ok(struct vm_area_struct *vma, pfn_t pfn)
> >   {
> >     /* these checks mirror the abort conditions in vm_normal_page */

Am 23.01.24 um 09:33 schrieb Zhou, Xianrong:
> [AMD Official Use Only - General]
>
>>> The vmf_insert_pfn_prot could cause unnecessary double faults on a
>>> device pfn. Because currently the vmf_insert_pfn_prot does not make
>>> the pfn writable so the pte entry is normally read-only or dirty
>>> catching.
>> What? How do you got to this conclusion?
> Sorry. I did not mention that this problem only exists on arm64 platform.
Ok, that makes at least a little bit more sense.
> Because on arm64 platform the PTE_RDONLY is automatically attached to
> the userspace pte entries even through VM_WRITE + VM_SHARE.
> The  PTE_RDONLY needs to be cleared in vmf_insert_pfn_prot. However
> vmf_insert_pfn_prot do not make the pte writable passing false @mkwrite
> to insert_pfn.
Question is why is arm64 doing this? As far as I can see they must have 
some hardware reason for that.

The mkwrite parameter to insert_pfn() was added by commit b2770da642540 
to make insert_pfn() look more like insert_pfn_pmd() so that the DAX 
code can insert PTEs which are writable and dirty at the same time.

This is a completely different use case to what you try to use it here 
for and that looks extremely fishy to me.

Regards,
Christian.
>
>>> The first fault only sets up the pte entry which actually is dirty
>>> catching. And the second immediate fault to the pfn due to first
dirty
>>> catching when the cpu re-execute the store instruction.
>> It could be that this is done to work around some hw behavior, but not
>> because of dirty catching.
>>
>>> Normally if the drivers call vmf_insert_pfn_prot and also supply
>>> 'pfn_mkwrite' callback within vm_operations_struct which
requires the
>>> pte to be dirty catching then the vmf_insert_pfn_prot and the
double
>>> fault are reasonable. It is not a problem.
>> Well, as far as I can see that behavior absolutely doesn't make
sense.
>>
>> When pfn_mkwrite is requested then the driver should use PAGE_COPY,
which
>> is exactly what VMWGFX (the only driver using dirty tracking) is doing.
>>
>> Everybody else uses PAGE_SHARED which should make the pte writeable
>> immediately.
>>
>> Regards,
>> Christian.
>>
>>> However the most of drivers calling vmf_insert_pfn_prot do not
supply
>>> the 'pfn_mkwrite' callback so that the second fault is
unnecessary.
>>>
>>> So just like vmf_insert_mixed and vmf_insert_mixed_mkwrite pair, we
>>> should also supply vmf_insert_pfn_mkwrite for drivers as well.
>>>
>>> Signed-off-by: Xianrong Zhou <Xianrong.Zhou at amd.com>
>>> ---
>>>    arch/x86/entry/vdso/vma.c                  |  3 ++-
>>>    drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c    |  2 +-
>>>    drivers/gpu/drm/i915/gem/i915_gem_ttm.c    |  2 +-
>>>    drivers/gpu/drm/nouveau/nouveau_gem.c      |  2 +-
>>>    drivers/gpu/drm/radeon/radeon_gem.c        |  2 +-
>>>    drivers/gpu/drm/ttm/ttm_bo_vm.c            |  8 +++++---
>>>    drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c |  8 +++++---
>>>    include/drm/ttm/ttm_bo.h                   |  3 ++-
>>>    include/linux/mm.h                         |  2 +-
>>>    mm/memory.c                                | 14 +++++++++++---
>>>    10 files changed, 30 insertions(+), 16 deletions(-)
>>>
>>> diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
>>> index 7645730dc228..dd2431c2975f 100644
>>> --- a/arch/x86/entry/vdso/vma.c
>>> +++ b/arch/x86/entry/vdso/vma.c
>>> @@ -185,7 +185,8 @@ static vm_fault_t vvar_fault(const struct
>> vm_special_mapping *sm,
>>>              if (pvti &&
vclock_was_used(VDSO_CLOCKMODE_PVCLOCK))
>> {
>>>                      return vmf_insert_pfn_prot(vma,
vmf->address,
>>>                                      __pa(pvti) >>
PAGE_SHIFT,
>>> -                                   pgprot_decrypted(vma-
>>> vm_page_prot));
>>> +                                   pgprot_decrypted(vma-
>>> vm_page_prot),
>>> +                                   true);
>>>              }
>>>      } else if (sym_offset == image->sym_hvclock_page) {
>>>              pfn = hv_get_tsc_pfn();
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>> index 49a5f1c73b3e..adcb20d9e624 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>> @@ -64,7 +64,7 @@ static vm_fault_t amdgpu_gem_fault(struct
vm_fault
>> *vmf)
>>>              }
>>>
>>>              ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma-
>>> vm_page_prot,
>>> -                                          TTM_BO_VM_NUM_PREFAULT);
>>> +                                          TTM_BO_VM_NUM_PREFAULT,
>> true);
>>>              drm_dev_exit(idx);
>>>      } else {
>>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
>>> b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
>>> index 9227f8146a58..c6f13ae6c308 100644
>>> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
>>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
>>> @@ -1114,7 +1114,7 @@ static vm_fault_t vm_fault_ttm(struct
vm_fault
>>> *vmf)
>>>
>>>      if (drm_dev_enter(dev, &idx)) {
>>>              ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma-
>>> vm_page_prot,
>>> -                                          TTM_BO_VM_NUM_PREFAULT);
>>> +                                          TTM_BO_VM_NUM_PREFAULT,
>> true);
>>>              drm_dev_exit(idx);
>>>      } else {
>>>              ret = ttm_bo_vm_dummy_page(vmf, vmf->vma-
>>> vm_page_prot); diff
>>> --git a/drivers/gpu/drm/nouveau/nouveau_gem.c
>>> b/drivers/gpu/drm/nouveau/nouveau_gem.c
>>> index 49c2bcbef129..7e1453762ec9 100644
>>> --- a/drivers/gpu/drm/nouveau/nouveau_gem.c
>>> +++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
>>> @@ -56,7 +56,7 @@ static vm_fault_t nouveau_ttm_fault(struct
vm_fault
>>> *vmf)
>>>
>>>      nouveau_bo_del_io_reserve_lru(bo);
>>>      prot = vm_get_page_prot(vma->vm_flags);
>>> -   ret = ttm_bo_vm_fault_reserved(vmf, prot,
>> TTM_BO_VM_NUM_PREFAULT);
>>> +   ret = ttm_bo_vm_fault_reserved(vmf, prot,
>> TTM_BO_VM_NUM_PREFAULT,
>>> +true);
>>>      nouveau_bo_add_io_reserve_lru(bo);
>>>      if (ret == VM_FAULT_RETRY && !(vmf->flags &
>> FAULT_FLAG_RETRY_NOWAIT))
>>>              return ret;
>>> diff --git a/drivers/gpu/drm/radeon/radeon_gem.c
>>> b/drivers/gpu/drm/radeon/radeon_gem.c
>>> index 3fec3acdaf28..b21cf00ae162 100644
>>> --- a/drivers/gpu/drm/radeon/radeon_gem.c
>>> +++ b/drivers/gpu/drm/radeon/radeon_gem.c
>>> @@ -62,7 +62,7 @@ static vm_fault_t radeon_gem_fault(struct
vm_fault
>> *vmf)
>>>              goto unlock_resv;
>>>
>>>      ret = ttm_bo_vm_fault_reserved(vmf,
vmf->vma->vm_page_prot,
>>> -                                  TTM_BO_VM_NUM_PREFAULT);
>>> +                                  TTM_BO_VM_NUM_PREFAULT, true);
>>>      if (ret == VM_FAULT_RETRY && !(vmf->flags &
>> FAULT_FLAG_RETRY_NOWAIT))
>>>              goto unlock_mclk;
>>>
>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c
>>> b/drivers/gpu/drm/ttm/ttm_bo_vm.c index
>> 4212b8c91dd4..7d14a7d267aa
>>> 100644
>>> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
>>> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
>>> @@ -167,6 +167,7 @@ EXPORT_SYMBOL(ttm_bo_vm_reserve);
>>>     * @num_prefault: Maximum number of prefault pages. The caller
may
>> want to
>>>     * specify this based on madvice settings and the size of the
GPU object
>>>     * backed by the memory.
>>> + * @mkwrite: make the pfn or page writable
>>>     *
>>>     * This function inserts one or more page table entries pointing
to the
>>>     * memory backing the buffer object, and then returns a return
code
>>> @@ -180,7 +181,8 @@ EXPORT_SYMBOL(ttm_bo_vm_reserve);
>>>     */
>>>    vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
>>>                                  pgprot_t prot,
>>> -                               pgoff_t num_prefault)
>>> +                               pgoff_t num_prefault,
>>> +                               bool mkwrite)
>>>    {
>>>      struct vm_area_struct *vma = vmf->vma;
>>>      struct ttm_buffer_object *bo = vma->vm_private_data; @@
-263,7
>>> +265,7 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
>>>               * at arbitrary times while the data is mmap'ed.
>>>               * See vmf_insert_pfn_prot() for a discussion.
>>>               */
>>> -           ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
>>> +           ret = vmf_insert_pfn_prot(vma, address, pfn, prot,
mkwrite);
>>>
>>>              /* Never error on prefaulted PTEs */
>>>              if (unlikely((ret & VM_FAULT_ERROR))) { @@ -312,7
+314,7
>> @@
>>> vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t
prot)
>>>      /* Prefault the entire VMA range right away to avoid further
faults */
>>>      for (address = vma->vm_start; address < vma->vm_end;
>>>           address += PAGE_SIZE)
>>> -           ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
>>> +           ret = vmf_insert_pfn_prot(vma, address, pfn, prot,
true);
>>>
>>>      return ret;
>>>    }
>>> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
>>> b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
>>> index 74ff2812d66a..bb8e4b641681 100644
>>> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
>>> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
>>> @@ -452,12 +452,14 @@ vm_fault_t vmw_bo_vm_fault(struct vm_fault
>> *vmf)
>>>       * sure the page protection is write-enabled so we don't
get
>>>       * a lot of unnecessary write faults.
>>>       */
>>> -   if (vbo->dirty && vbo->dirty->method ==
VMW_BO_DIRTY_MKWRITE)
>>> +   if (vbo->dirty && vbo->dirty->method ==
VMW_BO_DIRTY_MKWRITE)
>> {
>>>              prot = vm_get_page_prot(vma->vm_flags &
~VM_SHARED);
>>> -   else
>>> +           ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault,
>> false);
>>> +   } else {
>>>              prot = vm_get_page_prot(vma->vm_flags);
>>> +           ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault,
>> true);
>>> +   }
>>>
>>> -   ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault);
>>>      if (ret == VM_FAULT_RETRY && !(vmf->flags &
>> FAULT_FLAG_RETRY_NOWAIT))
>>>              return ret;
>>>
>>> diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
index
>>> 0223a41a64b2..66e293db69ee 100644
>>> --- a/include/drm/ttm/ttm_bo.h
>>> +++ b/include/drm/ttm/ttm_bo.h
>>> @@ -386,7 +386,8 @@ vm_fault_t ttm_bo_vm_reserve(struct
>> ttm_buffer_object *bo,
>>>                           struct vm_fault *vmf);
>>>    vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
>>>                                  pgprot_t prot,
>>> -                               pgoff_t num_prefault);
>>> +                               pgoff_t num_prefault,
>>> +                               bool mkwrite);
>>>    vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf);
>>>    void ttm_bo_vm_open(struct vm_area_struct *vma);
>>>    void ttm_bo_vm_close(struct vm_area_struct *vma); diff --git
>>> a/include/linux/mm.h b/include/linux/mm.h index
>>> f5a97dec5169..f8868e28ea04 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -3553,7 +3553,7 @@ int vm_map_pages_zero(struct vm_area_struct
>> *vma, struct page **pages,
>>>    vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned
long
>> addr,
>>>                      unsigned long pfn);
>>>    vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma,
unsigned
>> long addr,
>>> -                   unsigned long pfn, pgprot_t pgprot);
>>> +                   unsigned long pfn, pgprot_t pgprot, bool
mkwrite);
>>>    vm_fault_t vmf_insert_mixed(struct vm_area_struct *vma, unsigned
long
>> addr,
>>>                      pfn_t pfn);
>>>    vm_fault_t vmf_insert_mixed_mkwrite(struct vm_area_struct *vma,
diff
>>> --git a/mm/memory.c b/mm/memory.c index 7e1f4849463a..2c28f1a349ff
>>> 100644
>>> --- a/mm/memory.c
>>> +++ b/mm/memory.c
>>> @@ -2195,6 +2195,7 @@ static vm_fault_t insert_pfn(struct
>> vm_area_struct *vma, unsigned long addr,
>>>     * @addr: target user address of this page
>>>     * @pfn: source kernel pfn
>>>     * @pgprot: pgprot flags for the inserted page
>>> + * @mkwrite: make the pfn writable
>>>     *
>>>     * This is exactly like vmf_insert_pfn(), except that it allows
drivers
>>>     * to override pgprot on a per-page basis.
>>> @@ -2223,7 +2224,7 @@ static vm_fault_t insert_pfn(struct
>> vm_area_struct *vma, unsigned long addr,
>>>     * Return: vm_fault_t value.
>>>     */
>>>    vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma,
unsigned
>> long addr,
>>> -                   unsigned long pfn, pgprot_t pgprot)
>>> +                   unsigned long pfn, pgprot_t pgprot, bool
mkwrite)
>>>    {
>>>      /*
>>>       * Technically, architectures with pte_special can avoid all
these
>>> @@ -2246,7 +2247,7 @@ vm_fault_t vmf_insert_pfn_prot(struct
>> vm_area_struct *vma, unsigned long addr,
>>>      track_pfn_insert(vma, &pgprot, __pfn_to_pfn_t(pfn,
PFN_DEV));
>>>
>>>      return insert_pfn(vma, addr, __pfn_to_pfn_t(pfn, PFN_DEV),
pgprot,
>>> -                   false);
>>> +                   mkwrite);
>>>    }
>>>    EXPORT_SYMBOL(vmf_insert_pfn_prot);
>>>
>>> @@ -2273,10 +2274,17 @@ EXPORT_SYMBOL(vmf_insert_pfn_prot);
>>>    vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned
long
>> addr,
>>>                      unsigned long pfn)
>>>    {
>>> -   return vmf_insert_pfn_prot(vma, addr, pfn,
vma->vm_page_prot);
>>> +   return vmf_insert_pfn_prot(vma, addr, pfn,
vma->vm_page_prot,
>>> +false);
>>>    }
>>>    EXPORT_SYMBOL(vmf_insert_pfn);
>>>
>>> +vm_fault_t vmf_insert_pfn_mkwrite(struct vm_area_struct *vma,
unsigned
>> long addr,
>>> +                   unsigned long pfn)
>>> +{
>>> +   return vmf_insert_pfn_prot(vma, addr, pfn,
vma->vm_page_prot,
>> true);
>>> +} EXPORT_SYMBOL(vmf_insert_pfn_mkwrite);
>>> +
>>>    static bool vm_mixed_ok(struct vm_area_struct *vma, pfn_t pfn)
>>>    {
>>>      /* these checks mirror the abort conditions in vm_normal_page
*/