Nouveau - Aug 2019 - [PATCH 2/2] mm/hmm: hmm_range_fault() infinite loop

On Fri, Aug 23, 2019 at 03:17:53PM -0700, Ralph Campbell wrote:
> Signed-off-by: Ralph Campbell <rcampbell at nvidia.com>
>  mm/hmm.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 29371485fe94..4882b83aeccb 100644
> +++ b/mm/hmm.c
> @@ -292,6 +292,9 @@ static int hmm_vma_walk_hole_(unsigned long addr,
unsigned long end,
>  	hmm_vma_walk->last = addr;
>  	i = (addr - range->start) >> PAGE_SHIFT;
>  
> +	if (write_fault && walk->vma &&
!(walk->vma->vm_flags & VM_WRITE))
> +		return -EPERM;
Can walk->vma be NULL here? hmm_vma_do_fault() touches it
unconditionally.

Jason

On 8/27/19 11:41 AM, Jason Gunthorpe wrote:
> On Fri, Aug 23, 2019 at 03:17:53PM -0700, Ralph Campbell wrote:
> 
>> Signed-off-by: Ralph Campbell <rcampbell at nvidia.com>
>>   mm/hmm.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/mm/hmm.c b/mm/hmm.c
>> index 29371485fe94..4882b83aeccb 100644
>> +++ b/mm/hmm.c
>> @@ -292,6 +292,9 @@ static int hmm_vma_walk_hole_(unsigned long addr,
unsigned long end,
>>   	hmm_vma_walk->last = addr;
>>   	i = (addr - range->start) >> PAGE_SHIFT;
>>   
>> +	if (write_fault && walk->vma &&
!(walk->vma->vm_flags & VM_WRITE))
>> +		return -EPERM;
> 
> Can walk->vma be NULL here? hmm_vma_do_fault() touches it
> unconditionally.
> 
> Jason
> 
walk->vma can be NULL. hmm_vma_do_fault() no longer touches it
unconditionally, that is what the preceding patch fixes.
I suppose I could change hmm_vma_walk_hole_() to check for NULL
and fill in the pfns[] array, I just chose to handle it in
hmm_vma_do_fault().

On Tue, Aug 27, 2019 at 01:16:13PM -0700, Ralph Campbell
wrote:
> 
> On 8/27/19 11:41 AM, Jason Gunthorpe wrote:
> > On Fri, Aug 23, 2019 at 03:17:53PM -0700, Ralph Campbell wrote:
> > 
> > > Signed-off-by: Ralph Campbell <rcampbell at nvidia.com>
> > >   mm/hmm.c | 3 +++
> > >   1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/mm/hmm.c b/mm/hmm.c
> > > index 29371485fe94..4882b83aeccb 100644
> > > +++ b/mm/hmm.c
> > > @@ -292,6 +292,9 @@ static int hmm_vma_walk_hole_(unsigned long
addr, unsigned long end,
> > >   	hmm_vma_walk->last = addr;
> > >   	i = (addr - range->start) >> PAGE_SHIFT;
> > > +	if (write_fault && walk->vma &&
!(walk->vma->vm_flags & VM_WRITE))
> > > +		return -EPERM;
> > 
> > Can walk->vma be NULL here? hmm_vma_do_fault() touches it
> > unconditionally.
> > 
> > Jason
> > 
> walk->vma can be NULL. hmm_vma_do_fault() no longer touches it
> unconditionally, that is what the preceding patch fixes.
> I suppose I could change hmm_vma_walk_hole_() to check for NULL
> and fill in the pfns[] array, I just chose to handle it in
> hmm_vma_do_fault().
Okay, yes maybe long term it would be clearer to do the vma null check
closer to the start of the callback, but this is a good enough bug fix

Reviewed-by: Jason Gunthorpe <jgg at mellanox.com>

Jason