From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 374753DB62D; Thu, 30 Apr 2026 11:31:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777548718; cv=none; b=splggxmjLp9uknjWisywAOqSwYwYwhJ3JAilU3azy4KJ3w2n4NmBpx5o1G4CQJf1zUuaDfECKZRUnzF8+IcQhrXe3auWCOTocqer5F46R8/0MAb9cZHYTV/OjkT5tZ8u16EcOpEgOLDCRdujqKOi4q4ScQ69KqBTRokXYdXk0gA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777548718; c=relaxed/simple; bh=GAVeUYrfD81Vgxhl/4MJAOtYKmr0cjXk10/5oQ2nEDM=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=T06Fvebz7zj20MmNpB+EVGyY0n+sxIq7emTYgbMgnOL0HH4JpGG4RsRrfsP4iXK9hTiVnHroGgQV5Qwz86yyrT8nuq/9W/otECda1V1BFXh22xxYYaO7IoqwcJrqQ6khvDV3rDu8ppCucFEdfrLoKptCAGowuFk9fA2EDHmExVY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PO7A+Z6C; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PO7A+Z6C" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 68341C2BCB3; Thu, 30 Apr 2026 11:31:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777548715; bh=GAVeUYrfD81Vgxhl/4MJAOtYKmr0cjXk10/5oQ2nEDM=; h=From:Date:Subject:To:Cc:From; b=PO7A+Z6CSYSyfV7aQwYqp2SRHmj4kkRrsddLZMzbjtkDjEPu33pdvOLXg1x/cq7Ro tVFeT6roiky4eZBekVtFBAkyN+CpbWOyix2h/s5uO9+He9dYFBy4MhMgso2xGA9nnC z+2VpX4usUvmrArf3ScDgAmL0hh+fukLQ/dfr0SctDhJoRagc2mPhDok1GVJI5Zvbb hM96Jg//w7p6me4AW8RaKiO33otuDKipcx8MzGsI44vVitn8C/mdcvK9NFLnH28ADM QUFx638NESL+SkYYaF4pWrVrk/viM6e2oe6zL9ngteF0RcmTybjp6H0wkODsxZ6Pdj vQKkm8itzQPLw== From: "David Hildenbrand (Arm)" Date: Thu, 30 Apr 2026 13:31:22 +0200 Subject: [PATCH] mm: fix __vm_normal_page() to handle missing support for pmd_special()/pud_special() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260430-pmd_special-v1-1-dbcbcfd72c20@kernel.org> X-B4-Tracking: v=1; b=H4sIAIk982kC/6tWKk4tykwtVrJSqFYqSi3LLM7MzwNyDHUUlJIzE vPSU3UzU4B8JSMDIzMDE2MD3YLclPjigtTkzMQcXTNDg5SklBSLxGTjZCWgjoKi1LTMCrBp0bG 1tQDlEi9iXQAAAA== To: Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Oscar Salvador , Hugh Dickins , Lance Yang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Bibo Mao , stable@vger.kernel.org, "David Hildenbrand (Arm)" X-Mailer: b4 0.13.0 On x86 32-bit with THP enabled, zap_huge_pmd() is seen to generate a "WARNING: mm/memory.c:735 at __vm_normal_page+0x6a/0x7d", from the VM_WARN_ON_ONCE(is_zero_pfn(pfn) || is_huge_zero_pfn(pfn)); followed by "BUG: Bad rss-counter state"s, then later "BUG: Bad page state"s when reclaim gets to call shrink_huge_zero_folio_scan(). It's as if the _PAGE_SPECIAL bit never got set in the huge_zero pmd: and indeed, whereas pte_special() and pte_mkspecial() are subject to a dedicated CONFIG_ARCH_HAS_PTE_SPECIAL, pmd_special() and pmd_mkspecial() are subject to CONFIG_ARCH_SUPPORTS_PMD_PFNMAP, which is never enabled on any 32-bit architecture. While the problem was exposed through commit d80a9cb1a64a ("mm/huge_memory: add and use normal_or_softleaf_folio_pmd()"), it was an oversight in commit af38538801c6 ("mm/memory: factor out common code from vm_normal_page_*()") and would result in other problems: * huge zero folio accounted in smaps, pagemap (PAGE_IS_FILE) and numamaps as file-backed THP * folio_walk_start() returning the folio even without FW_ZEROPAGE set. Callers seem to tolerate that, though. ... and triggering the VM_WARN_ON_ONE(), although never reported so far. To fix it, teach vm_normal_page_pmd()/vm_normal_page_pud() to consider whether pmd_special/pud_special is actually implemented. Fixes: af38538801c6 ("mm/memory: factor out common code from vm_normal_page_*()") Reported-by: Hugh Dickins Closes: https://lore.kernel.org/r/74a75b59-2e13-3985-ee99-d5521f39df2a@google.com Reported-by: Bibo Mao Closes: https://lore.kernel.org/r/20260430041121.2839350-1-maobibo@loongson.cn Debugged-by: Hugh Dickins Reviewed-by: Lance Yang Tested-by: Bibo Mao Cc: stable@vger.kernel.org Signed-off-by: David Hildenbrand (Arm) --- This is an alternative to Hugh's patch, whereby we leave pmd_special() be a NOP and instead teach __vm_normal_page() about lack of support for pmd_special/pud_special. --- mm/memory.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 7322a40e73b9..4d84976fc7f4 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -612,6 +612,21 @@ static void print_bad_page_map(struct vm_area_struct *vma, dump_stack(); add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE); } + +static inline bool pgtable_level_has_pxx_special(enum pgtable_level level) +{ + switch (level) { + case PGTABLE_LEVEL_PTE: + return IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL); + case PGTABLE_LEVEL_PMD: + return IS_ENABLED(CONFIG_ARCH_SUPPORTS_PMD_PFNMAP); + case PGTABLE_LEVEL_PUD: + return IS_ENABLED(CONFIG_ARCH_SUPPORTS_PUD_PFNMAP); + default: + return false; + } +} + #define print_bad_pte(vma, addr, pte, page) \ print_bad_page_map(vma, addr, pte_val(pte), page, PGTABLE_LEVEL_PTE) @@ -684,7 +699,7 @@ static inline struct page *__vm_normal_page(struct vm_area_struct *vma, unsigned long addr, unsigned long pfn, bool special, unsigned long long entry, enum pgtable_level level) { - if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) { + if (pgtable_level_has_pxx_special(level)) { if (unlikely(special)) { #ifdef CONFIG_FIND_NORMAL_PAGE if (vma->vm_ops && vma->vm_ops->find_normal_page) @@ -699,8 +714,9 @@ static inline struct page *__vm_normal_page(struct vm_area_struct *vma, return NULL; } /* - * With CONFIG_ARCH_HAS_PTE_SPECIAL, any special page table - * mappings (incl. shared zero folios) are marked accordingly. + * With working pte_special()/pmd_special()..., any special page + * table mappings (incl. shared zero folios) are marked + * accordingly. */ } else { if (unlikely(vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))) { --- base-commit: d94322006a51b522dd361128a450bf9e75aad889 change-id: 20260430-pmd_special-610dbdd8ac3c -- Cheers, David