Am 07.06.21 um 18:13 schrieb Thomas Hellström (Intel):
On 6/7/21 3:58 PM, Christian König wrote:
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
Signed-off-by: Christian König christian.koenig@amd.com Bugs: https://gitlab.freedesktop.org/drm/amd/-/issues/1606#note_936174
drivers/gpu/drm/ttm/ttm_bo_vm.c | 44 +++++++++++---------------------- 1 file changed, 14 insertions(+), 30 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c index 61828488ae2b..c9edb75626d9 100644 --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c @@ -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 +549,16 @@ 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 VM_SHARED here since without it we would have really strange + * behavior on COW. + */
Nit: Perhaps "Enforce no COW.." since mappings are allowed with VM_SHARED iff VM_MAYWRITE is not set. Also style consistency with comments: First /* followed by line-break or are you adapting the above style for ttm?
Good point and no not really. I just sometimes forget to hit enter here and we don't have any automated script complaining.
With that fixed,
Reviewed-by: Thomas Hellström thomas.hellstrom@linux.intel.com
Thanks, Christian.
+ 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 +573,8 @@ 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);