[PATCH v3 1/1] drm/ttm: Fix COW check
Christian König
christian.koenig at amd.com
Wed Jul 14 10:51:15 UTC 2021
Am 14.07.21 um 12:44 schrieb Daniel Vetter:
> On Mon, Jul 12, 2021 at 06:06:36PM -0400, Felix Kuehling wrote:
>> KFD Thunk maps invisible VRAM BOs with PROT_NONE, MAP_PRIVATE.
>> is_cow_mapping returns true for these mappings. Add a check for
>> vm_flags & VM_WRITE to avoid mmap failures on private read-only or
>> PROT_NONE mappings.
>>
>> v2: protect against mprotect making a mapping writable after the fact
>> v3: update driver-specific vm_operations_structs
>>
>> Fixes: f91142c62161 ("drm/ttm: nuke VM_MIXEDMAP on BO mappings v3")
>> Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
>> Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
> So looking at vmf_insert_pfn_prot() and the comment there we can't have
> VM_PFNMAP and is_cow_mapping ever be true, or things break. On platforms
> without pte_special at least.
Key idea is that we never end up in vmf_insert_pfn_prot() because the
vma is mapped with PROT_NONE.
>
> So I'm not sure this is a great idea, and definitely not for all drivers
Yeah, I'm absolutely not happy with this either but it seemed to be the
least painful thing to do.
> ...
>
> Can we clear VM_MAYWRITE instead to force this to be a non-cow mapping
> instead?
Well we have considered forcefully setting VM_SHARED, which won't work
easily for a couple of reasons.
But clearing VM_MAYWRITE in amdgpu/amdkfd may actually work as well.
Felix can you test this?
Thanks,
Christian.
> -Daniel
>
>> ---
>> drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 3 ++-
>> drivers/gpu/drm/nouveau/nouveau_gem.c | 3 ++-
>> drivers/gpu/drm/radeon/radeon_gem.c | 3 ++-
>> drivers/gpu/drm/ttm/ttm_bo_vm.c | 14 +++++++++++++-
>> drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c | 1 +
>> include/drm/ttm/ttm_bo_api.h | 4 ++++
>> 6 files changed, 24 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>> index b3404c43a911..1aa750a6a5d2 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>> @@ -79,7 +79,8 @@ static const struct vm_operations_struct amdgpu_gem_vm_ops = {
>> .fault = amdgpu_gem_fault,
>> .open = ttm_bo_vm_open,
>> .close = ttm_bo_vm_close,
>> - .access = ttm_bo_vm_access
>> + .access = ttm_bo_vm_access,
>> + .mprotect = ttm_bo_vm_mprotect
>> };
>>
>> static void amdgpu_gem_object_free(struct drm_gem_object *gobj)
>> diff --git a/drivers/gpu/drm/nouveau/nouveau_gem.c b/drivers/gpu/drm/nouveau/nouveau_gem.c
>> index 5b27845075a1..164ea564bb7a 100644
>> --- a/drivers/gpu/drm/nouveau/nouveau_gem.c
>> +++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
>> @@ -70,7 +70,8 @@ static const struct vm_operations_struct nouveau_ttm_vm_ops = {
>> .fault = nouveau_ttm_fault,
>> .open = ttm_bo_vm_open,
>> .close = ttm_bo_vm_close,
>> - .access = ttm_bo_vm_access
>> + .access = ttm_bo_vm_access,
>> + .mprotect = ttm_bo_vm_mprotect
>> };
>>
>> void
>> diff --git a/drivers/gpu/drm/radeon/radeon_gem.c b/drivers/gpu/drm/radeon/radeon_gem.c
>> index 458f92a70887..c19ad07eb7b5 100644
>> --- a/drivers/gpu/drm/radeon/radeon_gem.c
>> +++ b/drivers/gpu/drm/radeon/radeon_gem.c
>> @@ -77,7 +77,8 @@ static const struct vm_operations_struct radeon_gem_vm_ops = {
>> .fault = radeon_gem_fault,
>> .open = ttm_bo_vm_open,
>> .close = ttm_bo_vm_close,
>> - .access = ttm_bo_vm_access
>> + .access = ttm_bo_vm_access,
>> + .mprotect = ttm_bo_vm_mprotect
>> };
>>
>> static void radeon_gem_object_free(struct drm_gem_object *gobj)
>> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
>> index f56be5bc0861..fb325bad5db6 100644
>> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
>> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
>> @@ -542,17 +542,29 @@ int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
>> }
>> EXPORT_SYMBOL(ttm_bo_vm_access);
>>
>> +int ttm_bo_vm_mprotect(struct vm_area_struct *vma, unsigned long start,
>> + unsigned long end, unsigned long newflags)
>> +{
>> + /* Enforce no COW since would have really strange behavior with it. */
>> + if (is_cow_mapping(newflags) && (newflags & VM_WRITE))
>> + return -EINVAL;
>> +
>> + return 0;
>> +}
>> +EXPORT_SYMBOL(ttm_bo_vm_mprotect);
>> +
>> static const struct vm_operations_struct ttm_bo_vm_ops = {
>> .fault = ttm_bo_vm_fault,
>> .open = ttm_bo_vm_open,
>> .close = ttm_bo_vm_close,
>> .access = ttm_bo_vm_access,
>> + .mprotect = ttm_bo_vm_mprotect,
>> };
>>
>> int ttm_bo_mmap_obj(struct vm_area_struct *vma, struct ttm_buffer_object *bo)
>> {
>> /* Enforce no COW since would have really strange behavior with it. */
>> - if (is_cow_mapping(vma->vm_flags))
>> + if (is_cow_mapping(vma->vm_flags) && (vma->vm_flags & VM_WRITE))
>> return -EINVAL;
>>
>> ttm_bo_get(bo);
>> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
>> index e6b1f98ec99f..e4bf7dc99320 100644
>> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
>> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
>> @@ -61,6 +61,7 @@ int vmw_mmap(struct file *filp, struct vm_area_struct *vma)
>> .fault = vmw_bo_vm_fault,
>> .open = ttm_bo_vm_open,
>> .close = ttm_bo_vm_close,
>> + .mprotect = ttm_bo_vm_mprotect,
>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> .huge_fault = vmw_bo_vm_huge_fault,
>> #endif
>> diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
>> index f681bbdbc698..40eb95875355 100644
>> --- a/include/drm/ttm/ttm_bo_api.h
>> +++ b/include/drm/ttm/ttm_bo_api.h
>> @@ -605,6 +605,10 @@ void ttm_bo_vm_close(struct vm_area_struct *vma);
>>
>> int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
>> void *buf, int len, int write);
>> +
>> +int ttm_bo_vm_mprotect(struct vm_area_struct *vma, unsigned long start,
>> + unsigned long end, unsigned long newflags);
>> +
>> bool ttm_bo_delayed_delete(struct ttm_device *bdev, bool remove_all);
>>
>> vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t prot);
>> --
>> 2.32.0
>>
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