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a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1790545548; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=KGNdxSSdZkDgEWIxbIrSONNvgQ0foWsTVx0VRCiF5LY=; b=vspAuQYBCoGkZREiOBESokitO27pMDCVn88HBcQG2ch32GL8IysSa5W+b4yahwhNFXQ5jk nNzDzO1voW5qaoBnJeHCyBCrwFcN4fw3BS1gAER/EAi4l94W2KPJSRKvwFK/GgrAAH1BHY grc7zKrDys1MiwWr5tDnokHUe3H9QHY= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id A5C6A60052; Sun, 27 Sep 2026 21:45:47 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CA0B31F000FF; Sun, 27 Sep 2026 21:45:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1790545547; bh=KGNdxSSdZkDgEWIxbIrSONNvgQ0foWsTVx0VRCiF5LY=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=QaJRi6ZQjZOcqFIQsABru6Fxu7eHrYrTmN+siAsqk6ml3AhbO3meqysbRPj+lNI9d 5s0Dt/o+tP2L/+sk7+SIhi8NR++NyRXnq9jc9lXF3inCKDMhOWT+0txtKu+Tn4kNy6 l8A7g6vag+IL1N22uGqH8srlrVQFjO3G3rKtOAFI= Date: Sun, 27 Sep 2026 14:45:46 -0700 From: Andrew Morton To: Gregory Price Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, liam@infradead.org, ljs@kernel.org, david@kernel.org, vbabka@kernel.org, jannh@google.com, ziy@nvidia.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, peterx@redhat.com, jgg@ziepe.ca, sashiko-bot Subject: Re: [PATCH v3 0/2] mm: stop calling pmd_folio() on special PMDs Message-Id: <20260927144546.5141169bddc0ff1868c8ec17@linux-foundation.org> In-Reply-To: <20260926105110.2156652-1-gourry@gourry.net> References: <20260926105110.2156652-1-gourry@gourry.net> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Stat-Signature: ktzstnt95xd4t4tge93puo4zhw431u3n X-Rspam-User: X-Rspamd-Queue-Id: 56F7140002 X-HE-Tag: 1790545548-971137 X-HE-Meta: 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 dIs0GtFv Le2Jcj7f6F38xlRDDCMBW8TZlqNnxLkVdsPaMJkkLbnIhwXioqr30tDn/JkOz2rJP4Lg7V/sGvVhtXdbaCBtfYn6Hsy7OGIxPmOL+uk5AQQ1hXtDNlqMmdKNvKIq71aWyIMGpsUEF3AspqdpqiZODntPUqAh22oW+2YRxqnnapjdlBL3XG7SrEjbKmbRdzZX+TvW8jB/XnlvicBAf6dtHEUvRKTtUIFDmwifnNg88ii+bxikSZw8MP40d5sA/O6tcspmREl0PwJDqYTOds5m1ksnLsJ/DMt8AlfK4dAsL6juKmDyo2aeCgMYvnVfcN1Ua4NeL/66P4sKm8X6TGq2l2tzq98mRDETJEhX1KffIyRvI11Ps+ZFxdhZWiO8lW9XJ9fNmWvjr/gHofN795p5LZoo1GBMHB6wVXNtCY24RCMAsx2NIA2PCNhrnxg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, 26 Sep 2026 06:51:08 -0400 Gregory Price wrote: > Two page table walkers resolve the folio behind a PMD with pmd_folio(), > which is only valid for a PMD mapping a refcounted struct page: > > madvise_cold_or_pageout_pte_range() mm/madvise.c > queue_folios_pmd() mm/mempolicy.c > > vmf_insert_pfn_pmd() installs special PMDs holding a raw pfn that need not > have a memmap entry at all. Both walkers can reach one and fault on the > first folio field read. The PTE halves of both already use > vm_normal_folio(); these two patches make the PMD halves match. > > The four callers of vmf_insert_pfn_pmd(), and which walker each reaches: > > drivers/vfio/pci/vfio_pci_core.c VM_PFNMAP mempolicy > drivers/gpu/drm/drm_gem_shmem_helper.c VM_PFNMAP mempolicy > drivers/gpu/drm/panthor/panthor_gem.c VM_PFNMAP mempolicy > drivers/hv/mshv_vtl_main.c VM_MIXEDMAP both > > can_madv_lru_vma() rejects VM_PFNMAP, so only mshv_vtl_low reaches the > madvise walker, and that needs CAP_SYS_ADMIN. queue_pages_walk_ops > supplies its own ->test_walk, so walk_page_test()'s generic VM_PFNMAP skip > never runs and vfio-pci is reachable by any process holding the device fd. > Hence the different stable tags. > > One behaviour change: mbind(MPOL_MF_STRICT) over a PMD mapped VM_PFNMAP > region now returns 0 rather than -EIO. The PTE loop already returned 0 > there. drm_gem_shmem and panthor are where this is observable, since they > PMD map pages that do have a memmap entry and so never faulted. Thanks, I've updated mm-unstable to this version. > v3: improvements from Lorenzo Here's how v3 altered mm.git: mm/mempolicy.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) --- a/mm/mempolicy.c~b +++ a/mm/mempolicy.c @@ -668,7 +668,7 @@ static inline bool queue_folio_required( } static void queue_folios_pmd(pmd_t *pmd, unsigned long addr, - struct mm_walk *walk) + struct mm_walk *walk) { struct folio *folio; struct queue_pages *qp = walk->private; @@ -680,12 +680,7 @@ static void queue_folios_pmd(pmd_t *pmd, return; } folio = vm_normal_folio_pmd(walk->vma, addr, pmdval); - if (!folio) { - if (is_huge_zero_pmd(pmdval)) - walk->action = ACTION_CONTINUE; - return; - } - if (folio_is_zone_device(folio)) + if (!folio || folio_is_zone_device(folio)) return; if (!queue_folio_required(folio, qp)) return; _