[PATCH] drm/ttm: Temporarily disable the huge_fault() callback

[PATCH] drm/ttm: Temporarily disable the huge_fault() callback

[Thomas Hellström (VMware)]

From: "Thomas Hellstrom (VMware)" <thomas_os@shipmail.org>

With amdgpu and CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y, there are
errors like:
BUG: non-zero pgtables_bytes on freeing mm
and:
BUG: Bad rss-counter state
with TTM transparent huge-pages.
Until we've figured out what other TTM drivers do differently compared to
vmwgfx, disable the huge_fault() callback, eliminating transhuge
page-table entries.

Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Thomas Hellstrom (VMware) <thomas_os@shipmail.org>
Reported-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
Tested-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
Acked-by: Christian König <christian.koenig@amd.com>
---
 drivers/gpu/drm/ttm/ttm_bo_vm.c | 63 ---------------------------------
 1 file changed, 63 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index 6ee3b96f0d13..0ad30b112982 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -442,66 +442,6 @@ vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
 }
 EXPORT_SYMBOL(ttm_bo_vm_fault);
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-/**
- * ttm_pgprot_is_wrprotecting - Is a page protection value write-protecting?
- * @prot: The page protection value
- *
- * Return: true if @prot is write-protecting. false otherwise.
- */
-static bool ttm_pgprot_is_wrprotecting(pgprot_t prot)
-{
-	/*
-	 * This is meant to say "pgprot_wrprotect(prot) == prot" in a generic
-	 * way. Unfortunately there is no generic pgprot_wrprotect.
-	 */
-	return pte_val(pte_wrprotect(__pte(pgprot_val(prot)))) ==
-		pgprot_val(prot);
-}
-
-static vm_fault_t ttm_bo_vm_huge_fault(struct vm_fault *vmf,
-				       enum page_entry_size pe_size)
-{
-	struct vm_area_struct *vma = vmf->vma;
-	pgprot_t prot;
-	struct ttm_buffer_object *bo = vma->vm_private_data;
-	vm_fault_t ret;
-	pgoff_t fault_page_size = 0;
-	bool write = vmf->flags & FAULT_FLAG_WRITE;
-
-	switch (pe_size) {
-	case PE_SIZE_PMD:
-		fault_page_size = HPAGE_PMD_SIZE >> PAGE_SHIFT;
-		break;
-#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
-	case PE_SIZE_PUD:
-		fault_page_size = HPAGE_PUD_SIZE >> PAGE_SHIFT;
-		break;
-#endif
-	default:
-		WARN_ON_ONCE(1);
-		return VM_FAULT_FALLBACK;
-	}
-
-	/* Fallback on write dirty-tracking or COW */
-	if (write && ttm_pgprot_is_wrprotecting(vma->vm_page_prot))
-		return VM_FAULT_FALLBACK;
-
-	ret = ttm_bo_vm_reserve(bo, vmf);
-	if (ret)
-		return ret;
-
-	prot = vm_get_page_prot(vma->vm_flags);
-	ret = ttm_bo_vm_fault_reserved(vmf, prot, 1, fault_page_size);
-	if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
-		return ret;
-
-	dma_resv_unlock(bo->base.resv);
-
-	return ret;
-}
-#endif
-
 void ttm_bo_vm_open(struct vm_area_struct *vma)
 {
 	struct ttm_buffer_object *bo = vma->vm_private_data;
@@ -604,9 +544,6 @@ static const struct vm_operations_struct ttm_bo_vm_ops = {
 	.open = ttm_bo_vm_open,
 	.close = ttm_bo_vm_close,
 	.access = ttm_bo_vm_access,
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	.huge_fault = ttm_bo_vm_huge_fault,
-#endif
 };
 
 static struct ttm_buffer_object *ttm_bo_vm_lookup(struct ttm_bo_device *bdev,
-- 
2.21.1

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Re: [PATCH] drm/ttm: Temporarily disable the huge_fault() callback

[Thomas Hellström (VMware)]

Dave, Christian,

Could any of you pick this up (I'm currently on vacation) to have a 
chance of getting it in before -rc1?
Thanks,
Thomas


On 4/9/20 6:49 PM, Thomas Hellström (VMware) wrote:
> From: "Thomas Hellstrom (VMware)" <thomas_os@shipmail.org>
>
> With amdgpu and CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y, there are
> errors like:
> BUG: non-zero pgtables_bytes on freeing mm
> and:
> BUG: Bad rss-counter state
> with TTM transparent huge-pages.
> Until we've figured out what other TTM drivers do differently compared to
> vmwgfx, disable the huge_fault() callback, eliminating transhuge
> page-table entries.
>
> Cc: Christian König <christian.koenig@amd.com>
> Signed-off-by: Thomas Hellstrom (VMware) <thomas_os@shipmail.org>
> Reported-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
> Tested-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
> Acked-by: Christian König <christian.koenig@amd.com>
> ---
>   drivers/gpu/drm/ttm/ttm_bo_vm.c | 63 ---------------------------------
>   1 file changed, 63 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index 6ee3b96f0d13..0ad30b112982 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> @@ -442,66 +442,6 @@ vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
>   }
>   EXPORT_SYMBOL(ttm_bo_vm_fault);
>   
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -/**
> - * ttm_pgprot_is_wrprotecting - Is a page protection value write-protecting?
> - * @prot: The page protection value
> - *
> - * Return: true if @prot is write-protecting. false otherwise.
> - */
> -static bool ttm_pgprot_is_wrprotecting(pgprot_t prot)
> -{
> -	/*
> -	 * This is meant to say "pgprot_wrprotect(prot) == prot" in a generic
> -	 * way. Unfortunately there is no generic pgprot_wrprotect.
> -	 */
> -	return pte_val(pte_wrprotect(__pte(pgprot_val(prot)))) ==
> -		pgprot_val(prot);
> -}
> -
> -static vm_fault_t ttm_bo_vm_huge_fault(struct vm_fault *vmf,
> -				       enum page_entry_size pe_size)
> -{
> -	struct vm_area_struct *vma = vmf->vma;
> -	pgprot_t prot;
> -	struct ttm_buffer_object *bo = vma->vm_private_data;
> -	vm_fault_t ret;
> -	pgoff_t fault_page_size = 0;
> -	bool write = vmf->flags & FAULT_FLAG_WRITE;
> -
> -	switch (pe_size) {
> -	case PE_SIZE_PMD:
> -		fault_page_size = HPAGE_PMD_SIZE >> PAGE_SHIFT;
> -		break;
> -#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> -	case PE_SIZE_PUD:
> -		fault_page_size = HPAGE_PUD_SIZE >> PAGE_SHIFT;
> -		break;
> -#endif
> -	default:
> -		WARN_ON_ONCE(1);
> -		return VM_FAULT_FALLBACK;
> -	}
> -
> -	/* Fallback on write dirty-tracking or COW */
> -	if (write && ttm_pgprot_is_wrprotecting(vma->vm_page_prot))
> -		return VM_FAULT_FALLBACK;
> -
> -	ret = ttm_bo_vm_reserve(bo, vmf);
> -	if (ret)
> -		return ret;
> -
> -	prot = vm_get_page_prot(vma->vm_flags);
> -	ret = ttm_bo_vm_fault_reserved(vmf, prot, 1, fault_page_size);
> -	if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
> -		return ret;
> -
> -	dma_resv_unlock(bo->base.resv);
> -
> -	return ret;
> -}
> -#endif
> -
>   void ttm_bo_vm_open(struct vm_area_struct *vma)
>   {
>   	struct ttm_buffer_object *bo = vma->vm_private_data;
> @@ -604,9 +544,6 @@ static const struct vm_operations_struct ttm_bo_vm_ops = {
>   	.open = ttm_bo_vm_open,
>   	.close = ttm_bo_vm_close,
>   	.access = ttm_bo_vm_access,
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -	.huge_fault = ttm_bo_vm_huge_fault,
> -#endif
>   };
>   
>   static struct ttm_buffer_object *ttm_bo_vm_lookup(struct ttm_bo_device *bdev,


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Re: [PATCH] drm/ttm: Temporarily disable the huge_fault() callback

[Dave Airlie]

On Fri, 10 Apr 2020 at 02:51, Thomas Hellström (VMware)
<thomas_os@shipmail.org> wrote:
>
> Dave, Christian,
>
> Could any of you pick this up (I'm currently on vacation) to have a
> chance of getting it in before -rc1?

I'll pull this in directly to fixes today.

Dave.

> Thanks,
> Thomas
>
>
> On 4/9/20 6:49 PM, Thomas Hellström (VMware) wrote:
> > From: "Thomas Hellstrom (VMware)" <thomas_os@shipmail.org>
> >
> > With amdgpu and CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y, there are
> > errors like:
> > BUG: non-zero pgtables_bytes on freeing mm
> > and:
> > BUG: Bad rss-counter state
> > with TTM transparent huge-pages.
> > Until we've figured out what other TTM drivers do differently compared to
> > vmwgfx, disable the huge_fault() callback, eliminating transhuge
> > page-table entries.
> >
> > Cc: Christian König <christian.koenig@amd.com>
> > Signed-off-by: Thomas Hellstrom (VMware) <thomas_os@shipmail.org>
> > Reported-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
> > Tested-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
> > Acked-by: Christian König <christian.koenig@amd.com>
> > ---
> >   drivers/gpu/drm/ttm/ttm_bo_vm.c | 63 ---------------------------------
> >   1 file changed, 63 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > index 6ee3b96f0d13..0ad30b112982 100644
> > --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > @@ -442,66 +442,6 @@ vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> >   }
> >   EXPORT_SYMBOL(ttm_bo_vm_fault);
> >
> > -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > -/**
> > - * ttm_pgprot_is_wrprotecting - Is a page protection value write-protecting?
> > - * @prot: The page protection value
> > - *
> > - * Return: true if @prot is write-protecting. false otherwise.
> > - */
> > -static bool ttm_pgprot_is_wrprotecting(pgprot_t prot)
> > -{
> > -     /*
> > -      * This is meant to say "pgprot_wrprotect(prot) == prot" in a generic
> > -      * way. Unfortunately there is no generic pgprot_wrprotect.
> > -      */
> > -     return pte_val(pte_wrprotect(__pte(pgprot_val(prot)))) ==
> > -             pgprot_val(prot);
> > -}
> > -
> > -static vm_fault_t ttm_bo_vm_huge_fault(struct vm_fault *vmf,
> > -                                    enum page_entry_size pe_size)
> > -{
> > -     struct vm_area_struct *vma = vmf->vma;
> > -     pgprot_t prot;
> > -     struct ttm_buffer_object *bo = vma->vm_private_data;
> > -     vm_fault_t ret;
> > -     pgoff_t fault_page_size = 0;
> > -     bool write = vmf->flags & FAULT_FLAG_WRITE;
> > -
> > -     switch (pe_size) {
> > -     case PE_SIZE_PMD:
> > -             fault_page_size = HPAGE_PMD_SIZE >> PAGE_SHIFT;
> > -             break;
> > -#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> > -     case PE_SIZE_PUD:
> > -             fault_page_size = HPAGE_PUD_SIZE >> PAGE_SHIFT;
> > -             break;
> > -#endif
> > -     default:
> > -             WARN_ON_ONCE(1);
> > -             return VM_FAULT_FALLBACK;
> > -     }
> > -
> > -     /* Fallback on write dirty-tracking or COW */
> > -     if (write && ttm_pgprot_is_wrprotecting(vma->vm_page_prot))
> > -             return VM_FAULT_FALLBACK;
> > -
> > -     ret = ttm_bo_vm_reserve(bo, vmf);
> > -     if (ret)
> > -             return ret;
> > -
> > -     prot = vm_get_page_prot(vma->vm_flags);
> > -     ret = ttm_bo_vm_fault_reserved(vmf, prot, 1, fault_page_size);
> > -     if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
> > -             return ret;
> > -
> > -     dma_resv_unlock(bo->base.resv);
> > -
> > -     return ret;
> > -}
> > -#endif
> > -
> >   void ttm_bo_vm_open(struct vm_area_struct *vma)
> >   {
> >       struct ttm_buffer_object *bo = vma->vm_private_data;
> > @@ -604,9 +544,6 @@ static const struct vm_operations_struct ttm_bo_vm_ops = {
> >       .open = ttm_bo_vm_open,
> >       .close = ttm_bo_vm_close,
> >       .access = ttm_bo_vm_access,
> > -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > -     .huge_fault = ttm_bo_vm_huge_fault,
> > -#endif
> >   };
> >
> >   static struct ttm_buffer_object *ttm_bo_vm_lookup(struct ttm_bo_device *bdev,
>
>
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[PATCH] drm/ttm: Temporarily disable the huge_fault() callback

[Thomas Hellström (VMware)]

From: "Thomas Hellstrom (VMware)" <thomas_os@shipmail.org>

With amdgpu and CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y, there are
errors like:
BUG: non-zero pgtables_bytes on freeing mm
and:
BUG: Bad rss-counter state
with TTM transparent huge-pages.
Until we've figured out what other TTM drivers do differently compared to
vmwgfx, disable the huge_fault() callback, eliminating transhuge
page-table entries.

Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Thomas Hellstrom (VMware) <thomas_os@shipmail.org>
Reported-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
Tested-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
---
 drivers/gpu/drm/ttm/ttm_bo_vm.c | 63 ---------------------------------
 1 file changed, 63 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index 6ee3b96f0d13..0ad30b112982 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -442,66 +442,6 @@ vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
 }
 EXPORT_SYMBOL(ttm_bo_vm_fault);
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-/**
- * ttm_pgprot_is_wrprotecting - Is a page protection value write-protecting?
- * @prot: The page protection value
- *
- * Return: true if @prot is write-protecting. false otherwise.
- */
-static bool ttm_pgprot_is_wrprotecting(pgprot_t prot)
-{
-	/*
-	 * This is meant to say "pgprot_wrprotect(prot) == prot" in a generic
-	 * way. Unfortunately there is no generic pgprot_wrprotect.
-	 */
-	return pte_val(pte_wrprotect(__pte(pgprot_val(prot)))) ==
-		pgprot_val(prot);
-}
-
-static vm_fault_t ttm_bo_vm_huge_fault(struct vm_fault *vmf,
-				       enum page_entry_size pe_size)
-{
-	struct vm_area_struct *vma = vmf->vma;
-	pgprot_t prot;
-	struct ttm_buffer_object *bo = vma->vm_private_data;
-	vm_fault_t ret;
-	pgoff_t fault_page_size = 0;
-	bool write = vmf->flags & FAULT_FLAG_WRITE;
-
-	switch (pe_size) {
-	case PE_SIZE_PMD:
-		fault_page_size = HPAGE_PMD_SIZE >> PAGE_SHIFT;
-		break;
-#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
-	case PE_SIZE_PUD:
-		fault_page_size = HPAGE_PUD_SIZE >> PAGE_SHIFT;
-		break;
-#endif
-	default:
-		WARN_ON_ONCE(1);
-		return VM_FAULT_FALLBACK;
-	}
-
-	/* Fallback on write dirty-tracking or COW */
-	if (write && ttm_pgprot_is_wrprotecting(vma->vm_page_prot))
-		return VM_FAULT_FALLBACK;
-
-	ret = ttm_bo_vm_reserve(bo, vmf);
-	if (ret)
-		return ret;
-
-	prot = vm_get_page_prot(vma->vm_flags);
-	ret = ttm_bo_vm_fault_reserved(vmf, prot, 1, fault_page_size);
-	if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
-		return ret;
-
-	dma_resv_unlock(bo->base.resv);
-
-	return ret;
-}
-#endif
-
 void ttm_bo_vm_open(struct vm_area_struct *vma)
 {
 	struct ttm_buffer_object *bo = vma->vm_private_data;
@@ -604,9 +544,6 @@ static const struct vm_operations_struct ttm_bo_vm_ops = {
 	.open = ttm_bo_vm_open,
 	.close = ttm_bo_vm_close,
 	.access = ttm_bo_vm_access,
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	.huge_fault = ttm_bo_vm_huge_fault,
-#endif
 };
 
 static struct ttm_buffer_object *ttm_bo_vm_lookup(struct ttm_bo_device *bdev,
-- 
2.21.1

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Re: [PATCH] drm/ttm: Temporarily disable the huge_fault() callback

[Thomas Hellström (VMware)]

Hi, Christian,

On 4/8/20 1:53 PM, Thomas Hellström (VMware) wrote:
> From: "Thomas Hellstrom (VMware)" <thomas_os@shipmail.org>
>
> With amdgpu and CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y, there are
> errors like:
> BUG: non-zero pgtables_bytes on freeing mm
> and:
> BUG: Bad rss-counter state
> with TTM transparent huge-pages.
> Until we've figured out what other TTM drivers do differently compared to
> vmwgfx, disable the huge_fault() callback, eliminating transhuge
> page-table entries.
>
> Cc: Christian König <christian.koenig@amd.com>
> Signed-off-by: Thomas Hellstrom (VMware) <thomas_os@shipmail.org>
> Reported-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
> Tested-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
> ---

Without being able to test and track this down on amdgpu there's little 
more than this I can do at the moment. Hopefully I'll be able to test on 
nouveau/ttm after getting back from vacation to see if I can reproduce.

It looks like some part of the kernel mistakes a huge page-table entry 
for a page directory, and that would be a path that is not hit with vmwgfx.

/Thomas


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Re: [PATCH] drm/ttm: Temporarily disable the huge_fault() callback

[Christian König]

Am 08.04.20 um 14:01 schrieb Thomas Hellström (VMware):
> Hi, Christian,
>
> On 4/8/20 1:53 PM, Thomas Hellström (VMware) wrote:
>> From: "Thomas Hellstrom (VMware)" <thomas_os@shipmail.org>
>>
>> With amdgpu and CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y, there are
>> errors like:
>> BUG: non-zero pgtables_bytes on freeing mm
>> and:
>> BUG: Bad rss-counter state
>> with TTM transparent huge-pages.
>> Until we've figured out what other TTM drivers do differently 
>> compared to
>> vmwgfx, disable the huge_fault() callback, eliminating transhuge
>> page-table entries.
>>
>> Cc: Christian König <christian.koenig@amd.com>
>> Signed-off-by: Thomas Hellstrom (VMware) <thomas_os@shipmail.org>
>> Reported-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
>> Tested-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>

Acked-by: Christian König <christian.koenig@amd.com>

>> ---
>
> Without being able to test and track this down on amdgpu there's 
> little more than this I can do at the moment. Hopefully I'll be able 
> to test on nouveau/ttm after getting back from vacation to see if I 
> can reproduce.
>
> It looks like some part of the kernel mistakes a huge page-table entry 
> for a page directory, and that would be a path that is not hit with 
> vmwgfx.

Well that looks like an ugly one and I don't know enough about the page 
table handling to hunt this down either.

BTW: Have you seen the coverity warning about  "WARN_ON_ONCE(ret = 
VM_FAULT_FALLBACK);"?

Regards,
Christian.

>
> /Thomas
>
>

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Re: [PATCH] drm/ttm: Temporarily disable the huge_fault() callback

[Thomas Hellström (VMware)]

On 4/8/20 2:19 PM, Christian König wrote:
> Am 08.04.20 um 14:01 schrieb Thomas Hellström (VMware):
>> Hi, Christian,
>>
>> On 4/8/20 1:53 PM, Thomas Hellström (VMware) wrote:
>>> From: "Thomas Hellstrom (VMware)" <thomas_os@shipmail.org>
>>>
>>> With amdgpu and CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y, there are
>>> errors like:
>>> BUG: non-zero pgtables_bytes on freeing mm
>>> and:
>>> BUG: Bad rss-counter state
>>> with TTM transparent huge-pages.
>>> Until we've figured out what other TTM drivers do differently 
>>> compared to
>>> vmwgfx, disable the huge_fault() callback, eliminating transhuge
>>> page-table entries.
>>>
>>> Cc: Christian König <christian.koenig@amd.com>
>>> Signed-off-by: Thomas Hellstrom (VMware) <thomas_os@shipmail.org>
>>> Reported-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
>>> Tested-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
>
> Acked-by: Christian König <christian.koenig@amd.com>
>
>>> ---
>>
>> Without being able to test and track this down on amdgpu there's 
>> little more than this I can do at the moment. Hopefully I'll be able 
>> to test on nouveau/ttm after getting back from vacation to see if I 
>> can reproduce.
>>
>> It looks like some part of the kernel mistakes a huge page-table 
>> entry for a page directory, and that would be a path that is not hit 
>> with vmwgfx.
>
> Well that looks like an ugly one and I don't know enough about the 
> page table handling to hunt this down either.
>
> BTW: Have you seen the coverity warning about  "WARN_ON_ONCE(ret = 
> VM_FAULT_FALLBACK);"?

Yes, that's a false warning but it might be that it should be rewritten 
for clarity like so:

ret = VM_FAULT_FALLBACK;
WARN_ON_ONCE(true);

/Thomas



>
> Regards,
> Christian.
>
>>
>> /Thomas
>>
>>

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Re: [PATCH] drm/ttm: Temporarily disable the huge_fault() callback

[Christian König]

Am 08.04.20 um 15:49 schrieb Thomas Hellström (VMware):
> On 4/8/20 2:19 PM, Christian König wrote:
>> Am 08.04.20 um 14:01 schrieb Thomas Hellström (VMware):
>>> Hi, Christian,
>>>
>>> On 4/8/20 1:53 PM, Thomas Hellström (VMware) wrote:
>>>> From: "Thomas Hellstrom (VMware)" <thomas_os@shipmail.org>
>>>>
>>>> With amdgpu and CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y, there are
>>>> errors like:
>>>> BUG: non-zero pgtables_bytes on freeing mm
>>>> and:
>>>> BUG: Bad rss-counter state
>>>> with TTM transparent huge-pages.
>>>> Until we've figured out what other TTM drivers do differently 
>>>> compared to
>>>> vmwgfx, disable the huge_fault() callback, eliminating transhuge
>>>> page-table entries.
>>>>
>>>> Cc: Christian König <christian.koenig@amd.com>
>>>> Signed-off-by: Thomas Hellstrom (VMware) <thomas_os@shipmail.org>
>>>> Reported-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
>>>> Tested-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
>>
>> Acked-by: Christian König <christian.koenig@amd.com>
>>
>>>> ---
>>>
>>> Without being able to test and track this down on amdgpu there's 
>>> little more than this I can do at the moment. Hopefully I'll be able 
>>> to test on nouveau/ttm after getting back from vacation to see if I 
>>> can reproduce.
>>>
>>> It looks like some part of the kernel mistakes a huge page-table 
>>> entry for a page directory, and that would be a path that is not hit 
>>> with vmwgfx.
>>
>> Well that looks like an ugly one and I don't know enough about the 
>> page table handling to hunt this down either.
>>
>> BTW: Have you seen the coverity warning about  "WARN_ON_ONCE(ret = 
>> VM_FAULT_FALLBACK);"?
>
> Yes, that's a false warning but it might be that it should be 
> rewritten for clarity like so:
>
> ret = VM_FAULT_FALLBACK;
> WARN_ON_ONCE(true);

Using an additional () also usually works, but I'm not even sure if 
WARN_ON_ONCE() isn't compiled to a no-op under some circumstances.

So better save than sorry,
Christian.

>
> /Thomas
>
>
>
>>
>> Regards,
>> Christian.
>>
>>>
>>> /Thomas
>>>
>>>
>

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