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Tue, 27 Jan 2026 14:53:41 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 8R3NFnXReGmgXAAAD6G6ig (envelope-from ); Tue, 27 Jan 2026 14:53:41 +0000 Message-ID: <2bcc0da5-e3b8-4980-8e26-d8215ae53120@suse.de> Date: Tue, 27 Jan 2026 15:53:40 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] drm/gem-shmem: Map pages in mmap fault handler To: Boris Brezillon Cc: loic.molinari@collabora.com, willy@infradead.org, maarten.lankhorst@linux.intel.com, mripard@kernel.org, airlied@gmail.com, simona@ffwll.ch, frank.binns@imgtec.com, matt.coster@imgtec.com, dri-devel@lists.freedesktop.org, linux-mm@kvack.org References: <20260127132938.429288-1-tzimmermann@suse.de> <20260127132938.429288-2-tzimmermann@suse.de> <20260127154511.6e2b9008@fedora> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; keydata= xsBNBFs50uABCADEHPidWt974CaxBVbrIBwqcq/WURinJ3+2WlIrKWspiP83vfZKaXhFYsdg XH47fDVbPPj+d6tQrw5lPQCyqjwrCPYnq3WlIBnGPJ4/jreTL6V+qfKRDlGLWFjZcsrPJGE0 BeB5BbqP5erN1qylK9i3gPoQjXGhpBpQYwRrEyQyjuvk+Ev0K1Jc5tVDeJAuau3TGNgah4Yc hdHm3bkPjz9EErV85RwvImQ1dptvx6s7xzwXTgGAsaYZsL8WCwDaTuqFa1d1jjlaxg6+tZsB 9GluwvIhSezPgnEmimZDkGnZRRSFiGP8yjqTjjWuf0bSj5rUnTGiyLyRZRNGcXmu6hjlABEB AAHNJ1Rob21hcyBaaW1tZXJtYW5uIDx0emltbWVybWFubkBzdXNlLmRlPsLAjgQTAQgAOAIb AwULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftODH AAoJEGgNwR1TC3ojx1wH/0hKGWugiqDgLNXLRD/4TfHBEKmxIrmfu9Z5t7vwUKfwhFL6hqvo lXPJJKQpQ2z8+X2vZm/slsLn7J1yjrOsoJhKABDi+3QWWSGkaGwRJAdPVVyJMfJRNNNIKwVb U6B1BkX2XDKDGffF4TxlOpSQzdtNI/9gleOoUA8+jy8knnDYzjBNOZqLG2FuTdicBXblz0Mf vg41gd9kCwYXDnD91rJU8tzylXv03E75NCaTxTM+FBXPmsAVYQ4GYhhgFt8S2UWMoaaABLDe 7l5FdnLdDEcbmd8uLU2CaG4W2cLrUaI4jz2XbkcPQkqTQ3EB67hYkjiEE6Zy3ggOitiQGcqp j//OwE0EWznS4AEIAMYmP4M/V+T5RY5at/g7rUdNsLhWv1APYrh9RQefODYHrNRHUE9eosYb T6XMryR9hT8XlGOYRwKWwiQBoWSDiTMo/Xi29jUnn4BXfI2px2DTXwc22LKtLAgTRjP+qbU6 3Y0xnQN29UGDbYgyyK51DW3H0If2a3JNsheAAK+Xc9baj0LGIc8T9uiEWHBnCH+RdhgATnWW GKdDegUR5BkDfDg5O/FISymJBHx2Dyoklv5g4BzkgqTqwmaYzsl8UxZKvbaxq0zbehDda8lv hFXodNFMAgTLJlLuDYOGLK2AwbrS3Sp0AEbkpdJBb44qVlGm5bApZouHeJ/+n+7r12+lqdsA EQEAAcLAdgQYAQgAIAIbDBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftOH6AAoJEGgNwR1T C3ojVSkIALpAPkIJPQoURPb1VWjh34l0HlglmYHvZszJWTXYwavHR8+k6Baa6H7ufXNQtThR yIxJrQLW6rV5lm7TjhffEhxVCn37+cg0zZ3j7zIsSS0rx/aMwi6VhFJA5hfn3T0TtrijKP4A SAQO9xD1Zk9/61JWk8OysuIh7MXkl0fxbRKWE93XeQBhIJHQfnc+YBLprdnxR446Sh8Wn/2D Ya8cavuWf2zrB6cZurs048xe0UbSW5AOSo4V9M0jzYI4nZqTmPxYyXbm30Kvmz0rYVRaitYJ 4kyYYMhuULvrJDMjZRvaNe52tkKAvMevcGdt38H4KSVXAylqyQOW5zvPc4/sq9c= In-Reply-To: <20260127154511.6e2b9008@fedora> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 518B61C0007 X-Stat-Signature: jtnry775c3z38bwono6znp7dx6awu6kz X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1769525623-540753 X-HE-Meta: U2FsdGVkX1+rlsgtl0dKj3G+IMsxMtoFIBfheYzA8TAfFfigyE2TYZdbnFB98hIN4UL+AbTbkiLVa5SARFP1ERKTGu/rvI7aUaKV3PO13f8TPX9D8A4cfAA6DPuhmxKAgo2MtnWZdhBxhRL2UumviVnNwoZAzMvGNTSCMrAd++8n36SRyOi34J7q4389P1llOM7xOyVFOuFf4X+hFptXzTbwJxN9LM79i4Swhy1tMRAK560EuJf97pp9S6bhgJMCGLqeY0qa0OnFFG2mbwoosOifgGsVl6wOkcg+4GWx4j8D77WwhOrlI5sSZinfSy+0VvuwoXhTFi7zBOlG1lL6zi+4whZFs4NHeGzYtVIEEgiyxHOcuJnEpyZAscMy+hfFZFw/98UAdXXxrX3Tfw2Cq0uBfivcynGkMckoVWYZAyXmwkH+Zthap2T+3NHN5dKZrSEhLcfHyfPjt/JWcLM6QWZklyvzzrSSC50sxFgt/Y1qmcokaRtkwpAzP4yaJwoS9xf3NYM6YWq5+5TccyoX7hZJaYBRmFsyfQxtOweqM1SxHzA2QsSeYr8vKWrEAYjaQqmW1EszM/4d/0qnkuaJ7KTQt4F+2N8N9OnJ9mDOJnjYkV4RIzmNuwlcm5IXKPMBZFiFxp8wABGQWdclr2hDLBmosjo+4LoVkh9xATTUWBurgi3wZA0Yt3gawX6pkGNbydXg9YYnmHNFqbY6UvlAIj51fD1iHcUDaYekOKEyk3mtfuxf9noGY5OzOFyO4M3UaqI3Wv7NsqEklcLIt8oAEUkTg8rqMYIqDF0lQVZsrWOXZ99whREhkVFqMkoWVrp1Bcj6a85ijkL7oTzx4zwNrwj82pyA+qPzZ3D/BhDMH8qXYet6br4NCjWnbg+ue1AS9EMagozZ7rFBXkpA1LCRe9smZx6i31256MOzhvE7zngF9gxjfS5DDnkT+VA2Jk2K/uvJFlE8Q5I5L2qA9fc ofZdWEbl SLL72loTkpv/JtsaoL+ZmYMvhhRp89sh7eVplyosR0txun2zxG9o1Zk7gcQ/vE6dXFAeobnm0VTKplgeiFPCs1H+8YGu4L5u3MktyyXRAN4f6J2SiMyDeZAn5pBjBJoKWHvw0ex4oQvC2KCZyl7VYlW+dYXxF8qm20l+YNCDFu1UMayusCKI8lFTSS3pgcwA+2YTLL4eCHAlxMR1H7pxQZ+O/5aJ9ECGw5kayNx0rH10oqeMCNqr8zP7iAkE1+75V7yWwDOrVwu8mTc/sSCpaT0csSF183XvQoRQIuG5D8tb/OPscu4QJo1aEz1lehL7LGbuELNt2cLKzKwc9WHzdKPkMSro/chaXwrmBlTgBBUfWb6TGDFRsXWRKw8iO1pxp/ju5pXpaRQmsNVU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, thanks for reviewing. Am 27.01.26 um 15:45 schrieb Boris Brezillon: > Hello Thomas, > > On Tue, 27 Jan 2026 14:16:36 +0100 > Thomas Zimmermann wrote: > >> Gem-shmem operates on pages instead of I/O memory ranges, so use them >> for mmap. This will allow for tracking page dirty/accessed flags. If >> hugepage support is available, insert the page's folio if possible. >> Otherwise fall back to mapping individual pages. >> >> As the PFN is no longer required for hugepage mappings, simplify the >> related code and make it depend on CONFIG_TRANSPARENT_HUGEPAGE. Prepare >> for tracking folio status. >> >> Signed-off-by: Thomas Zimmermann >> --- >> drivers/gpu/drm/drm_gem_shmem_helper.c | 58 ++++++++++++++++---------- >> 1 file changed, 35 insertions(+), 23 deletions(-) >> >> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c >> index 3871a6d92f77..b6ddabbfcc52 100644 >> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c >> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c >> @@ -553,17 +553,18 @@ EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create); >> static bool drm_gem_shmem_try_map_pmd(struct vm_fault *vmf, unsigned long addr, >> struct page *page) >> { >> -#ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP >> - unsigned long pfn = page_to_pfn(page); >> - unsigned long paddr = pfn << PAGE_SHIFT; >> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE >> + phys_addr_t paddr = page_to_phys(page); >> bool aligned = (addr & ~PMD_MASK) == (paddr & ~PMD_MASK); >> >> - if (aligned && >> - pmd_none(*vmf->pmd) && >> - folio_test_pmd_mappable(page_folio(page))) { >> - pfn &= PMD_MASK >> PAGE_SHIFT; >> - if (vmf_insert_pfn_pmd(vmf, pfn, false) == VM_FAULT_NOPAGE) >> - return true; >> + if (aligned && pmd_none(*vmf->pmd)) { >> + struct folio *folio = page_folio(page); >> + >> + if (folio_test_pmd_mappable(folio)) { >> + /* Read-only mapping; split upon write fault */ >> + if (vmf_insert_folio_pmd(vmf, folio, false) == VM_FAULT_NOPAGE) >> + return true; >> + } >> } >> #endif >> >> @@ -576,13 +577,10 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf) >> 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; >> - vm_fault_t ret; >> struct page **pages = shmem->pages; >> - pgoff_t page_offset; >> - unsigned long pfn; >> - >> - /* Offset to faulty address in the VMA. */ >> - page_offset = vmf->pgoff - vma->vm_pgoff; >> + pgoff_t page_offset = vmf->pgoff - vma->vm_pgoff; /* page offset within VMA */ >> + struct page *page = pages[page_offset]; >> + vm_fault_t ret; >> >> dma_resv_lock(shmem->base.resv, NULL); >> >> @@ -590,21 +588,35 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf) >> drm_WARN_ON_ONCE(obj->dev, !shmem->pages) || >> shmem->madv < 0) { >> ret = VM_FAULT_SIGBUS; >> - goto out; >> + goto err_dma_resv_unlock; >> } >> >> - if (drm_gem_shmem_try_map_pmd(vmf, vmf->address, pages[page_offset])) { >> - ret = VM_FAULT_NOPAGE; >> - goto out; >> + page = pages[page_offset]; >> + if (!page) { >> + ret = VM_FAULT_SIGBUS; >> + goto err_dma_resv_unlock; >> } >> >> - pfn = page_to_pfn(pages[page_offset]); >> - ret = vmf_insert_pfn(vma, vmf->address, pfn); >> + if (drm_gem_shmem_try_map_pmd(vmf, vmf->address, page)) { >> + ret = VM_FAULT_NOPAGE; >> + } else { >> + struct folio *folio = page_folio(page); >> + >> + get_page(page); >> + >> + folio_lock(folio); >> + >> + vmf->page = page; >> + ret = VM_FAULT_LOCKED; >> + } >> >> - out: >> dma_resv_unlock(shmem->base.resv); >> >> return ret; >> + >> +err_dma_resv_unlock: >> + dma_resv_unlock(shmem->base.resv); >> + return ret; > Why do we need an error path that's exactly the same as the success > path? I just found the explicit roll-back code easier to work with. But the other style does it as well. Noted for the next iteration. Best regards Thomas > >> } >> >> static void drm_gem_shmem_vm_open(struct vm_area_struct *vma) >> @@ -691,7 +703,7 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct >> if (ret) >> return ret; >> >> - vm_flags_set(vma, VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP); >> + vm_flags_mod(vma, VM_DONTEXPAND | VM_DONTDUMP, VM_PFNMAP); >> vma->vm_page_prot = vm_get_page_prot(vma->vm_flags); >> if (shmem->map_wc) >> vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot); > The rest looks reasonable, if everyone is happy with the less > restrictive aspect that !PFNMAP implies, as mentioned by Matthew. -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)