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drm/ttm: nuke VM_MIXEDMAP on BO mappings v3

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We discussed if that is really the right approach for quite a while now, but
digging deeper into a bug report on arm turned out that this is actually
horrible broken right now.

The reason for this is that vmf_insert_mixed_prot() always tries to grab
a reference to the underlaying page on architectures without
ARCH_HAS_PTE_SPECIAL and as far as I can see also enabled GUP.

So nuke using VM_MIXEDMAP here and use VM_PFNMAP instead.

Also make sure to reject mappings without VM_SHARED.

v2: reject COW mappings, merge function with only caller
v3: adjust comment as suggested by Thomas

Signed-off-by: Christian König <christian.koenig@amd.com>
Bugs: https://gitlab.freedesktop.org/drm/amd/-/issues/1606#note_936174
Link: https://patchwork.freedesktop.org/patch/msgid/20210607135830.8574-1-christian.koenig@amd.com
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
This commit is contained in:
Christian König 2021-06-01 19:47:50 +02:00
parent ceb515ba29
commit f91142c621
1 changed files with 12 additions and 30 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

42
drivers/gpu/drm/ttm/ttm_bo_vm.c
View file

@ -359,12 +359,7 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
* at arbitrary times while the data is mmap'ed.
* See vmf_insert_mixed_prot() for a discussion.
*/
if (vma->vm_flags & VM_MIXEDMAP)
ret = vmf_insert_mixed_prot(vma, address,
__pfn_to_pfn_t(pfn, PFN_DEV),
prot);
else
ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
/* Never error on prefaulted PTEs */
if (unlikely((ret & VM_FAULT_ERROR))) {
@ -411,15 +406,9 @@ vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t prot)
pfn = page_to_pfn(page);
/* Prefault the entire VMA range right away to avoid further faults */
for (address = vma->vm_start; address < vma->vm_end; address += PAGE_SIZE) {
if (vma->vm_flags & VM_MIXEDMAP)
ret = vmf_insert_mixed_prot(vma, address,
__pfn_to_pfn_t(pfn, PFN_DEV),
prot);
else
ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
}
for (address = vma->vm_start; address < vma->vm_end;
address += PAGE_SIZE)
ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
return ret;
}
@ -560,8 +549,14 @@ static const struct vm_operations_struct ttm_bo_vm_ops = {
.access = ttm_bo_vm_access,
};
static void ttm_bo_mmap_vma_setup(struct ttm_buffer_object *bo, struct vm_area_struct *vma)
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))
return -EINVAL;
ttm_bo_get(bo);
/*
* Drivers may want to override the vm_ops field. Otherwise we
* use TTM's default callbacks.
@ -576,21 +571,8 @@ static void ttm_bo_mmap_vma_setup(struct ttm_buffer_object *bo, struct vm_area_s
vma->vm_private_data = bo;
/*
* We'd like to use VM_PFNMAP on shared mappings, where
* (vma->vm_flags & VM_SHARED) != 0, for performance reasons,
* but for some reason VM_PFNMAP + x86 PAT + write-combine is very
* bad for performance. Until that has been sorted out, use
* VM_MIXEDMAP on all mappings. See freedesktop.org bug #75719
*/
vma->vm_flags |= VM_MIXEDMAP;
vma->vm_flags |= VM_PFNMAP;
vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
}
int ttm_bo_mmap_obj(struct vm_area_struct *vma, struct ttm_buffer_object *bo)
{
ttm_bo_get(bo);
ttm_bo_mmap_vma_setup(bo, vma);
return 0;
}
EXPORT_SYMBOL(ttm_bo_mmap_obj);