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Wed, 27 May 2026 12:18:38 +0200 (CEST) Date: Wed, 27 May 2026 12:18:32 +0200 From: Boris Brezillon To: Thomas Zimmermann Cc: Igor Torrente , loic.molinari@collabora.com, willy@infradead.org, frank.binns@imgtec.com, matt.coster@imgtec.com, maarten.lankhorst@linux.intel.com, mripard@kernel.org, airlied@gmail.com, simona@ffwll.ch, dri-devel@lists.freedesktop.org, linux-mm@kvack.org Subject: Re: [PATCH v3 5/6] drm/gem-shmem: Track folio accessed/dirty status in mmap Message-ID: <20260527121832.7264f0db@fedora> In-Reply-To: <67855fcd-2afe-4a1d-a51a-210e45f56167@suse.de> References: <20260209133241.238813-1-tzimmermann@suse.de> <20260209133241.238813-6-tzimmermann@suse.de> <850e8355-7884-405c-a70a-986ce032c019@suse.de> <831c0943-c75f-4d42-aa5f-90ce34cf8530@collabora.com> <67855fcd-2afe-4a1d-a51a-210e45f56167@suse.de> Organization: Collabora X-Mailer: Claws Mail 4.4.0 (GTK 3.24.52; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: 37rcbftcdkp9jzsankxxsx9gmipm76ui X-Rspamd-Queue-Id: 9436340012 X-Rspamd-Server: rspam07 X-Rspam-User: X-HE-Tag: 1779877121-138239 X-HE-Meta: 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 jCuM22hS tSW2aQViXvS5F2PlS9jYZerga7b6r4Hc/OYYCCleDmP5eDoAaDiKVuPFhPoUKPtSHf0oW8VWokH7Nh7eQpsqzKVqJ+uHWzPaU+kRj/M5+aKs1Pt4Di8Ox4CVoC3Nbz5/7u31jao2idbtnKRHBLNyWrRI4J785C/dZw0FkfuGeQjRMlYjT++d+WCW2dLBRkl+Zx7IG1askFt9Cf05qiqtbjPIsGgiqee3HkjXSr9mAbmZL8jKLKC49VHMkMFbEus8//mr9GShHkBa2Q2HbEifu1Ezi2MQ9ftbwBoUl Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello Thomas, I'm inlining the diff you posted so I can comment on it directly before it's officially posted to the list. On Wed, 27 May 2026 08:56:33 +0200 Thomas Zimmermann wrote: > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > index 545933c7f712..07e117673124 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -554,21 +554,6 @@ int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev, > } > EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create); > > -static void drm_gem_shmem_record_mkwrite(struct vm_fault *vmf) > -{ > - struct vm_area_struct *vma = vmf->vma; > - struct drm_gem_object *obj = vma->vm_private_data; > - struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj); > - loff_t num_pages = obj->size >> PAGE_SHIFT; > - pgoff_t page_offset = vmf->pgoff - vma->vm_pgoff; /* page offset within VMA */ > - > - if (drm_WARN_ON(obj->dev, !shmem->pages || page_offset >= num_pages)) > - return; > - > - file_update_time(vma->vm_file); > - folio_mark_dirty(page_folio(shmem->pages[page_offset])); > -} > - > static vm_fault_t try_insert_pfn(struct vm_fault *vmf, unsigned int order, > unsigned long pfn) > { > @@ -581,23 +566,16 @@ static vm_fault_t try_insert_pfn(struct vm_fault *vmf, unsigned int order, > > if (aligned && > folio_test_pmd_mappable(page_folio(pfn_to_page(pfn)))) { > - vm_fault_t ret; > - > pfn &= PMD_MASK >> PAGE_SHIFT; > > - /* Unlike PTEs which are automatically upgraded to > + /* > + * Unlike PTEs which are automatically upgraded to > * writeable entries, the PMD upgrades go through > * .huge_fault(). Make sure we pass the "write" info > * along in that case. > - * This also means we have to record the write fault > - * here, instead of in .pfn_mkwrite(). > */ > - ret = vmf_insert_pfn_pmd(vmf, pfn, > - vmf->flags & FAULT_FLAG_WRITE); > - if (ret == VM_FAULT_NOPAGE && (vmf->flags & FAULT_FLAG_WRITE)) > - drm_gem_shmem_record_mkwrite(vmf); > - > - return ret; > + return vmf_insert_pfn_pmd(vmf, pfn, > + vmf->flags & FAULT_FLAG_WRITE); I believe we can go back to return vmf_insert_pfn_pmd(vmf, pfn, false); if the mappings are no longer adjusted to catch write accesses. > } > #endif > } > @@ -635,8 +613,15 @@ static vm_fault_t drm_gem_shmem_any_fault(struct vm_fault *vmf, unsigned int ord > pfn = page_to_pfn(page); > > ret = try_insert_pfn(vmf, order, pfn); > - if (ret == VM_FAULT_NOPAGE) > + if (ret == VM_FAULT_NOPAGE) { > folio_mark_accessed(folio); > + /* > + * Always record write access to the buffer. The natural > + * place would be pfn_mkwrite, but this breaks KVM. > + */ > + file_update_time(vma->vm_file); > + folio_mark_dirty(folio); We can be a bit smarter here: /* * Always record write access to the buffer if the * mapping is writeable. The natural place would be * pfn_mkwrite, but this breaks KVM. */ if (vma->vm_flags & VM_WRITE) { file_update_time(vma->vm_file); folio_mark_dirty(folio); } > + } The rest looks good to me. Regards, Boris