From 0d979509539ed1df883a30d442177ca7be609565 Mon Sep 17 00:00:00 2001 From: Jason Gunthorpe Date: Tue, 19 Oct 2021 20:27:31 -0300 Subject: drm/ttm: remove ttm_bo_vm_insert_huge() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The huge page functionality in TTM does not work safely because PUD and PMD entries do not have a special bit. get_user_pages_fast() considers any page that passed pmd_huge() as usable: if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd) || pmd_devmap(pmd))) { And vmf_insert_pfn_pmd_prot() unconditionally sets entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); eg on x86 the page will be _PAGE_PRESENT | PAGE_PSE. As such gup_huge_pmd() will try to deref a struct page: head = try_grab_compound_head(pmd_page(orig), refs, flags); and thus crash. Thomas further notices that the drivers are not expecting the struct page to be used by anything - in particular the refcount incr above will cause them to malfunction. Thus everything about this is not able to fully work correctly considering GUP_fast. Delete it entirely. It can return someday along with a proper PMD/PUD_SPECIAL bit in the page table itself to gate GUP_fast. Fixes: 314b6580adc5 ("drm/ttm, drm/vmwgfx: Support huge TTM pagefaults") Signed-off-by: Jason Gunthorpe Reviewed-by: Thomas Hellström Reviewed-by: Christian König [danvet: Update subject per Thomas' &Christian's review] Signed-off-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/0-v2-a44694790652+4ac-ttm_pmd_jgg@nvidia.com --- include/drm/ttm/ttm_bo_api.h | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'include/drm') diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h index 0551e2587f14..cd785cfa3123 100644 --- a/include/drm/ttm/ttm_bo_api.h +++ b/include/drm/ttm/ttm_bo_api.h @@ -584,8 +584,7 @@ vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo, vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf, pgprot_t prot, - pgoff_t num_prefault, - pgoff_t fault_page_size); + pgoff_t num_prefault); vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf); -- cgit v1.2.3-58-ga151