drm/i915: Call page_address() on page acquired with GFP_KERNEL flag

[PATCH] drm/i915: Call page_address() on page acquired with GFP_KERNEL flag

Posted by Sumitra Sharma 2 years, 7 months ago

Pages allocated with GFP_KERNEL cannot come from Highmem.
That is why there is no need to call kmap() on them.

Therefore, don't call kmap() on the page coming from
vma_res->bi.pages using for_each_sgt_page() in
i915_vma_coredump_create().

Use a plain page_address() to get the kernel address instead.

Signed-off-by: Sumitra Sharma <sumitraartsy@gmail.com>
---
 drivers/gpu/drm/i915/i915_gpu_error.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index f020c0086fbc..6f51cb4fc55c 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -1164,9 +1164,8 @@ i915_vma_coredump_create(const struct intel_gt *gt,
 
 			drm_clflush_pages(&page, 1);
 
-			s = kmap(page);
+			s = page_address(page);
 			ret = compress_page(compress, s, dst, false);
-			kunmap(page);
 
 			drm_clflush_pages(&page, 1);
 
-- 
2.25.1

Re: [PATCH] drm/i915: Call page_address() on page acquired with GFP_KERNEL flag

Posted by Tvrtko Ursulin 2 years, 7 months ago

On 14/06/2023 13:35, Sumitra Sharma wrote:
> Pages allocated with GFP_KERNEL cannot come from Highmem.
> That is why there is no need to call kmap() on them.

Are you sure it is GFP_KERNEL backed and not tmpfs? I am not sure myself 
so let me copy Matt and Thomas if they happen to know off hand.

Regards,

Tvrtko

> Therefore, don't call kmap() on the page coming from
> vma_res->bi.pages using for_each_sgt_page() in
> i915_vma_coredump_create().
> 
> Use a plain page_address() to get the kernel address instead.
> 
> Signed-off-by: Sumitra Sharma <sumitraartsy@gmail.com>
> ---
>   drivers/gpu/drm/i915/i915_gpu_error.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> index f020c0086fbc..6f51cb4fc55c 100644
> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> @@ -1164,9 +1164,8 @@ i915_vma_coredump_create(const struct intel_gt *gt,
>   
>   			drm_clflush_pages(&page, 1);
>   
> -			s = kmap(page);
> +			s = page_address(page);
>   			ret = compress_page(compress, s, dst, false);
> -			kunmap(page);
>   
>   			drm_clflush_pages(&page, 1);
>

Re: [Intel-gfx] [PATCH] drm/i915: Call page_address() on page acquired with GFP_KERNEL flag

Posted by Thomas Hellström (Intel) 2 years, 7 months ago

On 6/14/23 15:22, Tvrtko Ursulin wrote:
>
> On 14/06/2023 13:35, Sumitra Sharma wrote:
>> Pages allocated with GFP_KERNEL cannot come from Highmem.
>> That is why there is no need to call kmap() on them.
>
> Are you sure it is GFP_KERNEL backed and not tmpfs? I am not sure 
> myself so let me copy Matt and Thomas if they happen to know off hand.

It looks to me these are shmem pages or TTM pages. Both could be 
highmem. So I think kmap is the correct choice here.

/Thomas




>
> Regards,
>
> Tvrtko
>
>> Therefore, don't call kmap() on the page coming from
>> vma_res->bi.pages using for_each_sgt_page() in
>> i915_vma_coredump_create().
>>
>> Use a plain page_address() to get the kernel address instead.
>>
>> Signed-off-by: Sumitra Sharma <sumitraartsy@gmail.com>
>> ---
>>   drivers/gpu/drm/i915/i915_gpu_error.c | 3 +--
>>   1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c 
>> b/drivers/gpu/drm/i915/i915_gpu_error.c
>> index f020c0086fbc..6f51cb4fc55c 100644
>> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
>> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
>> @@ -1164,9 +1164,8 @@ i915_vma_coredump_create(const struct intel_gt 
>> *gt,
>>                 drm_clflush_pages(&page, 1);
>>   -            s = kmap(page);
>> +            s = page_address(page);
>>               ret = compress_page(compress, s, dst, false);
>> -            kunmap(page);
>>                 drm_clflush_pages(&page, 1);

Re: [Intel-gfx] [PATCH] drm/i915: Call page_address() on page acquired with GFP_KERNEL flag

Posted by Sumitra Sharma 2 years, 7 months ago

On Wed, Jun 14, 2023 at 05:30:25PM +0200, Thomas Hellström (Intel) wrote:
> 
> On 6/14/23 15:22, Tvrtko Ursulin wrote:
> > 
> > On 14/06/2023 13:35, Sumitra Sharma wrote:
> > > Pages allocated with GFP_KERNEL cannot come from Highmem.
> > > That is why there is no need to call kmap() on them.
> > 
> > Are you sure it is GFP_KERNEL backed and not tmpfs? I am not sure myself
> > so let me copy Matt and Thomas if they happen to know off hand.
>

Hello,

Yes it is true that the pages have not been acquired using the GFP_KERNEL.

I confused the allocation of the struct 'i915_vma_resource' tracking the 
pages with the allocation of the pages themselves.

This was noted by my mentor Ira Weiny <ira.weiny@intel.com>.

> It looks to me these are shmem pages or TTM pages. Both could be highmem. So
> I think kmap is the correct choice here.
> 

However, the kmap() will not be the correct choice here and kmap_local_page()
must be used instead. I have created a v2 patch for the same
https://lore.kernel.org/lkml/20230617180420.GA410966@sumitra.com/

Thank you for helping me.

Regards
Sumitra

> /Thomas
>
> 
> 
> 
> > 
> > Regards,
> > 
> > Tvrtko
> > 
> > > Therefore, don't call kmap() on the page coming from
> > > vma_res->bi.pages using for_each_sgt_page() in
> > > i915_vma_coredump_create().
> > > 
> > > Use a plain page_address() to get the kernel address instead.
> > > 
> > > Signed-off-by: Sumitra Sharma <sumitraartsy@gmail.com>
> > > ---
> > >   drivers/gpu/drm/i915/i915_gpu_error.c | 3 +--
> > >   1 file changed, 1 insertion(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c
> > > b/drivers/gpu/drm/i915/i915_gpu_error.c
> > > index f020c0086fbc..6f51cb4fc55c 100644
> > > --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> > > +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> > > @@ -1164,9 +1164,8 @@ i915_vma_coredump_create(const struct intel_gt
> > > *gt,
> > >                 drm_clflush_pages(&page, 1);
> > >   -            s = kmap(page);
> > > +            s = page_address(page);
> > >               ret = compress_page(compress, s, dst, false);
> > > -            kunmap(page);
> > >                 drm_clflush_pages(&page, 1);