thr3ads.net - Linux Virtualization - [PATCH 4/6] vhost_vdpa: support doorbell mapping via mmap [Jun 2020]

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Jason Wang

2020-Jun-02 06:49 UTC

[PATCH 4/6] vhost_vdpa: support doorbell mapping via mmap

On 2020/6/2 ??12:56, Michael S. Tsirkin wrote:> On Tue, Jun 02, 2020 at 03:22:49AM +0800, kbuild test robot wrote:
>> Hi Jason,
>>
>> I love your patch! Yet something to improve:
>>
>> [auto build test ERROR on vhost/linux-next]
>> [also build test ERROR on linus/master v5.7 next-20200529]
>> [if your patch is applied to the wrong git tree, please drop us a note
to help
>> improve the system. BTW, we also suggest to use '--base' option
to specify the
>> base tree in git format-patch, please
seehttps://stackoverflow.com/a/37406982]
>>
>>
url:https://github.com/0day-ci/linux/commits/Jason-Wang/vDPA-doorbell-mapping/20200531-070834
>> base:https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git 
linux-next
>> config: m68k-randconfig-r011-20200601 (attached as .config)
>> compiler: m68k-linux-gcc (GCC) 9.3.0
>> reproduce (this is a W=1 build):
>>         
wgethttps://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross  -O
~/bin/make.cross
>>          chmod +x ~/bin/make.cross
>>          # save the attached .config to linux build tree
>>          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross
ARCH=m68k
>>
>> If you fix the issue, kindly add following tag as appropriate
>> Reported-by: kbuild test robot<lkp at intel.com>
>>
>> All errors (new ones prefixed by >>, old ones prefixed by
<<):
>>
>> drivers/vhost/vdpa.c: In function 'vhost_vdpa_fault':
>>>> drivers/vhost/vdpa.c:754:22: error: implicit declaration of
function 'pgprot_noncached' [-Werror=implicit-function-declaration]
>> 754 |  vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>> |                      ^~~~~~~~~~~~~~~~
>>>> drivers/vhost/vdpa.c:754:22: error: incompatible types when
assigning to type 'pgprot_t' {aka 'struct <anonymous>'}
from type 'int'
>> cc1: some warnings being treated as errors
>>
>> vim +/pgprot_noncached +754 drivers/vhost/vdpa.c
>>
>>     742	
>>     743	static vm_fault_t vhost_vdpa_fault(struct vm_fault *vmf)
>>     744	{
>>     745		struct vhost_vdpa *v =
vmf->vma->vm_file->private_data;
>>     746		struct vdpa_device *vdpa = v->vdpa;
>>     747		const struct vdpa_config_ops *ops = vdpa->config;
>>     748		struct vdpa_notification_area notify;
>>     749		struct vm_area_struct *vma = vmf->vma;
>>     750		u16 index = vma->vm_pgoff;
>>     751	
>>     752		notify = ops->get_vq_notification(vdpa, index);
>>     753	
>>   > 754		vma->vm_page_prot =
pgprot_noncached(vma->vm_page_prot);
>>     755		if (remap_pfn_range(vma, vmf->address & PAGE_MASK,
>>     756				    notify.addr >> PAGE_SHIFT, PAGE_SIZE,
>>     757				    vma->vm_page_prot))
>>     758			return VM_FAULT_SIGBUS;
>>     759	
>>     760		return VM_FAULT_NOPAGE;
>>     761	}
>>     762	
> Yes well, all this remapping clearly has no chance to work
> on systems without CONFIG_MMU.

It looks to me mmap can work according to Documentation/nommu-mmap.txt. 
But I'm not sure it's worth to bother.

Thanks

>
>
>

Michael S. Tsirkin

2020-Jun-02 13:31 UTC

head link

[PATCH 4/6] vhost_vdpa: support doorbell mapping via mmap

On Tue, Jun 02, 2020 at 02:49:38PM +0800, Jason Wang
wrote:> 
> On 2020/6/2 ??12:56, Michael S. Tsirkin wrote:
> > On Tue, Jun 02, 2020 at 03:22:49AM +0800, kbuild test robot wrote:
> > > Hi Jason,
> > > 
> > > I love your patch! Yet something to improve:
> > > 
> > > [auto build test ERROR on vhost/linux-next]
> > > [also build test ERROR on linus/master v5.7 next-20200529]
> > > [if your patch is applied to the wrong git tree, please drop us a
note to help
> > > improve the system. BTW, we also suggest to use '--base'
option to specify the
> > > base tree in git format-patch, please
seehttps://stackoverflow.com/a/37406982]
> > > 
> > >
url:https://github.com/0day-ci/linux/commits/Jason-Wang/vDPA-doorbell-mapping/20200531-070834
> > >
base:https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git  linux-next
> > > config: m68k-randconfig-r011-20200601 (attached as .config)
> > > compiler: m68k-linux-gcc (GCC) 9.3.0
> > > reproduce (this is a W=1 build):
> > >         
wgethttps://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross  -O
~/bin/make.cross
> > >          chmod +x ~/bin/make.cross
> > >          # save the attached .config to linux build tree
> > >          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0
make.cross ARCH=m68k
> > > 
> > > If you fix the issue, kindly add following tag as appropriate
> > > Reported-by: kbuild test robot<lkp at intel.com>
> > > 
> > > All errors (new ones prefixed by >>, old ones prefixed by
<<):
> > > 
> > > drivers/vhost/vdpa.c: In function 'vhost_vdpa_fault':
> > > > > drivers/vhost/vdpa.c:754:22: error: implicit
declaration of function 'pgprot_noncached'
[-Werror=implicit-function-declaration]
> > > 754 |  vma->vm_page_prot =
pgprot_noncached(vma->vm_page_prot);
> > > |                      ^~~~~~~~~~~~~~~~
> > > > > drivers/vhost/vdpa.c:754:22: error: incompatible types
when assigning to type 'pgprot_t' {aka 'struct
<anonymous>'} from type 'int'
> > > cc1: some warnings being treated as errors
> > > 
> > > vim +/pgprot_noncached +754 drivers/vhost/vdpa.c
> > > 
> > >     742	
> > >     743	static vm_fault_t vhost_vdpa_fault(struct vm_fault *vmf)
> > >     744	{
> > >     745		struct vhost_vdpa *v =
vmf->vma->vm_file->private_data;
> > >     746		struct vdpa_device *vdpa = v->vdpa;
> > >     747		const struct vdpa_config_ops *ops = vdpa->config;
> > >     748		struct vdpa_notification_area notify;
> > >     749		struct vm_area_struct *vma = vmf->vma;
> > >     750		u16 index = vma->vm_pgoff;
> > >     751	
> > >     752		notify = ops->get_vq_notification(vdpa, index);
> > >     753	
> > >   > 754		vma->vm_page_prot =
pgprot_noncached(vma->vm_page_prot);
> > >     755		if (remap_pfn_range(vma, vmf->address &
PAGE_MASK,
> > >     756				    notify.addr >> PAGE_SHIFT, PAGE_SIZE,
> > >     757				    vma->vm_page_prot))
> > >     758			return VM_FAULT_SIGBUS;
> > >     759	
> > >     760		return VM_FAULT_NOPAGE;
> > >     761	}
> > >     762	
> > Yes well, all this remapping clearly has no chance to work
> > on systems without CONFIG_MMU.
> 
> 
> It looks to me mmap can work according to Documentation/nommu-mmap.txt. But
> I'm not sure it's worth to bother.
> 
> Thanks

Well

int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
                unsigned long pfn, unsigned long size, pgprot_t prot)
{
        if (addr != (pfn << PAGE_SHIFT))
                return -EINVAL;

        vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
        return 0;
}
EXPORT_SYMBOL(remap_pfn_range);


So things aren't going to work if you have a fixed PFN
which is the case of the hardware device.

> 
> > 
> > 
> >

Jason Wang

2020-Jun-03 04:18 UTC

head link

[PATCH 4/6] vhost_vdpa: support doorbell mapping via mmap

On 2020/6/2 ??9:31, Michael S. Tsirkin wrote:> On Tue, Jun 02, 2020 at 02:49:38PM +0800, Jason Wang wrote:
>> On 2020/6/2 ??12:56, Michael S. Tsirkin wrote:
>>> On Tue, Jun 02, 2020 at 03:22:49AM +0800, kbuild test robot wrote:
>>>> Hi Jason,
>>>>
>>>> I love your patch! Yet something to improve:
>>>>
>>>> [auto build test ERROR on vhost/linux-next]
>>>> [also build test ERROR on linus/master v5.7 next-20200529]
>>>> [if your patch is applied to the wrong git tree, please drop us
a note to help
>>>> improve the system. BTW, we also suggest to use
'--base' option to specify the
>>>> base tree in git format-patch, please
seehttps://stackoverflow.com/a/37406982]
>>>>
>>>>
url:https://github.com/0day-ci/linux/commits/Jason-Wang/vDPA-doorbell-mapping/20200531-070834
>>>>
base:https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git  linux-next
>>>> config: m68k-randconfig-r011-20200601 (attached as .config)
>>>> compiler: m68k-linux-gcc (GCC) 9.3.0
>>>> reproduce (this is a W=1 build):
>>>>          
wgethttps://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross  -O
~/bin/make.cross
>>>>           chmod +x ~/bin/make.cross
>>>>           # save the attached .config to linux build tree
>>>>           COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0
make.cross ARCH=m68k
>>>>
>>>> If you fix the issue, kindly add following tag as appropriate
>>>> Reported-by: kbuild test robot<lkp at intel.com>
>>>>
>>>> All errors (new ones prefixed by >>, old ones prefixed by
<<):
>>>>
>>>> drivers/vhost/vdpa.c: In function 'vhost_vdpa_fault':
>>>>>> drivers/vhost/vdpa.c:754:22: error: implicit
declaration of function 'pgprot_noncached'
[-Werror=implicit-function-declaration]
>>>> 754 |  vma->vm_page_prot =
pgprot_noncached(vma->vm_page_prot);
>>>> |                      ^~~~~~~~~~~~~~~~
>>>>>> drivers/vhost/vdpa.c:754:22: error: incompatible types
when assigning to type 'pgprot_t' {aka 'struct
<anonymous>'} from type 'int'
>>>> cc1: some warnings being treated as errors
>>>>
>>>> vim +/pgprot_noncached +754 drivers/vhost/vdpa.c
>>>>
>>>>      742	
>>>>      743	static vm_fault_t vhost_vdpa_fault(struct vm_fault
*vmf)
>>>>      744	{
>>>>      745		struct vhost_vdpa *v =
vmf->vma->vm_file->private_data;
>>>>      746		struct vdpa_device *vdpa = v->vdpa;
>>>>      747		const struct vdpa_config_ops *ops = vdpa->config;
>>>>      748		struct vdpa_notification_area notify;
>>>>      749		struct vm_area_struct *vma = vmf->vma;
>>>>      750		u16 index = vma->vm_pgoff;
>>>>      751	
>>>>      752		notify = ops->get_vq_notification(vdpa, index);
>>>>      753	
>>>>    > 754		vma->vm_page_prot =
pgprot_noncached(vma->vm_page_prot);
>>>>      755		if (remap_pfn_range(vma, vmf->address &
PAGE_MASK,
>>>>      756				    notify.addr >> PAGE_SHIFT, PAGE_SIZE,
>>>>      757				    vma->vm_page_prot))
>>>>      758			return VM_FAULT_SIGBUS;
>>>>      759	
>>>>      760		return VM_FAULT_NOPAGE;
>>>>      761	}
>>>>      762	
>>> Yes well, all this remapping clearly has no chance to work
>>> on systems without CONFIG_MMU.
>>
>> It looks to me mmap can work according to Documentation/nommu-mmap.txt.
But
>> I'm not sure it's worth to bother.
>>
>> Thanks
>
> Well
>
> int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
>                  unsigned long pfn, unsigned long size, pgprot_t prot)
> {
>          if (addr != (pfn << PAGE_SHIFT))
>                  return -EINVAL;
>
>          vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND |
VM_DONTDUMP;
>          return 0;
> }
> EXPORT_SYMBOL(remap_pfn_range);
>
>
> So things aren't going to work if you have a fixed PFN
> which is the case of the hardware device.

Looking at the implementation of some drivers e.g mtd_char. If I read 
the code correctly, we can do this by providing get_unmapped_area method 
and use physical address directly.

But start form CONFIG_MMU should be fine.? Do you prefer making 
vhost_vdpa depends on CONFIG_MMU or just fail mmap when CONFIG_MMU is 
not configured?

Thanks

>
>
>>>
>>>

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