From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E9EA7C83F27 for ; Tue, 22 Jul 2025 11:48:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=rCLpGdWUS8REAwOwDqtj2Tc6HRfOgEsVFR54SmJidZ8=; b=SoQBbyNBjQ2BKX9/Qftg0RKVhE VKhGPuTDljGQzqJC2Y1kSpmffpndlhQnIUFHafkbuvT772S/sYxPc3ZUBAX+MRCxC7JqOnJoN6Rpc PKiaD3wfZLDsdOxGIxkLDVkBPw9H81pxP9WHr0/4E1TwiQx6WROevDSk1qM/lkbbSx5A77J8Zddk4 NKReHTth/sGw1vu2toT3Md60+wQZuhqnF/lz75GKBGAxhgy1IVvAIx+QPxucFiiCAtrVyOVe8aCwN /i2cRcHbFj9IW1VmcXSTCbOve2zm/8mkm8jvvxpg9uirMVb4gv1QHCJwoeZS3T4AjlAp1JlDqS1Mj g64821Ew==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1ueBTg-00000002Ke1-2wDW; Tue, 22 Jul 2025 11:48:12 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1ueBH0-00000002IVE-3o1I for linux-arm-kernel@lists.infradead.org; Tue, 22 Jul 2025 11:35:08 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D8A33152B; Tue, 22 Jul 2025 04:35:00 -0700 (PDT) Received: from [10.1.30.167] (XHFQ2J9959.cambridge.arm.com [10.1.30.167]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6488A3F66E; Tue, 22 Jul 2025 04:35:03 -0700 (PDT) Message-ID: <8f375e61-1a6d-4d9c-8980-849c0ab29063@arm.com> Date: Tue, 22 Jul 2025 12:35:02 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 3/7] mm: Add batched versions of ptep_modify_prot_start/commit Content-Language: en-GB To: Dev Jain , akpm@linux-foundation.org Cc: david@redhat.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, vbabka@suse.cz, jannh@google.com, anshuman.khandual@arm.com, peterx@redhat.com, joey.gouly@arm.com, ioworker0@gmail.com, baohua@kernel.org, kevin.brodsky@arm.com, quic_zhenhuah@quicinc.com, christophe.leroy@csgroup.eu, yangyicong@hisilicon.com, linux-arm-kernel@lists.infradead.org, hughd@google.com, yang@os.amperecomputing.com, ziy@nvidia.com References: <20250718090244.21092-1-dev.jain@arm.com> <20250718090244.21092-4-dev.jain@arm.com> From: Ryan Roberts In-Reply-To: <20250718090244.21092-4-dev.jain@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250722_043507_055071_7D97206F X-CRM114-Status: GOOD ( 28.60 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 18/07/2025 10:02, Dev Jain wrote: > Batch ptep_modify_prot_start/commit in preparation for optimizing mprotect, > implementing them as a simple loop over the corresponding single pte > helpers. Architecture may override these helpers. > > Signed-off-by: Dev Jain Reviewed-by: Ryan Roberts > --- > include/linux/pgtable.h | 84 ++++++++++++++++++++++++++++++++++++++++- > mm/mprotect.c | 4 +- > 2 files changed, 85 insertions(+), 3 deletions(-) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index cf1515c163e2..e3b99920be05 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -1331,7 +1331,9 @@ static inline pte_t ptep_modify_prot_start(struct vm_area_struct *vma, > > /* > * Commit an update to a pte, leaving any hardware-controlled bits in > - * the PTE unmodified. > + * the PTE unmodified. The pte returned from ptep_modify_prot_start() may > + * additionally have young and/or dirty bits set where previously they were not, > + * so the updated pte may have these additional changes. nit: I still find this difficult to parse (Although I expect you might tell me that this is the text I suggested last time around :) ). I think you mean that "it is permissable for young and/or dirty bits to be set in old_pte, despite beling clear when originally returned by ptep_modify_prot_start()". Anyway, no big deal. I think we all know what it's getting at. Thanks, Ryan > */ > static inline void ptep_modify_prot_commit(struct vm_area_struct *vma, > unsigned long addr, > @@ -1340,6 +1342,86 @@ static inline void ptep_modify_prot_commit(struct vm_area_struct *vma, > __ptep_modify_prot_commit(vma, addr, ptep, pte); > } > #endif /* __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION */ > + > +/** > + * modify_prot_start_ptes - Start a pte protection read-modify-write transaction > + * over a batch of ptes, which protects against asynchronous hardware > + * modifications to the ptes. The intention is not to prevent the hardware from > + * making pte updates, but to prevent any updates it may make from being lost. > + * Please see the comment above ptep_modify_prot_start() for full description. > + * > + * @vma: The virtual memory area the pages are mapped into. > + * @addr: Address the first page is mapped at. > + * @ptep: Page table pointer for the first entry. > + * @nr: Number of entries. > + * > + * May be overridden by the architecture; otherwise, implemented as a simple > + * loop over ptep_modify_prot_start(), collecting the a/d bits from each pte > + * in the batch. > + * > + * Note that PTE bits in the PTE batch besides the PFN can differ. > + * > + * Context: The caller holds the page table lock. The PTEs map consecutive > + * pages that belong to the same folio. All other PTE bits must be identical for > + * all PTEs in the batch except for young and dirty bits. The PTEs are all in > + * the same PMD. > + */ > +#ifndef modify_prot_start_ptes > +static inline pte_t modify_prot_start_ptes(struct vm_area_struct *vma, > + unsigned long addr, pte_t *ptep, unsigned int nr) > +{ > + pte_t pte, tmp_pte; > + > + pte = ptep_modify_prot_start(vma, addr, ptep); > + while (--nr) { > + ptep++; > + addr += PAGE_SIZE; > + tmp_pte = ptep_modify_prot_start(vma, addr, ptep); > + if (pte_dirty(tmp_pte)) > + pte = pte_mkdirty(pte); > + if (pte_young(tmp_pte)) > + pte = pte_mkyoung(pte); > + } > + return pte; > +} > +#endif > + > +/** > + * modify_prot_commit_ptes - Commit an update to a batch of ptes, leaving any > + * hardware-controlled bits in the PTE unmodified. > + * > + * @vma: The virtual memory area the pages are mapped into. > + * @addr: Address the first page is mapped at. > + * @ptep: Page table pointer for the first entry. > + * @old_pte: Old page table entry (for the first entry) which is now cleared. > + * @pte: New page table entry to be set. > + * @nr: Number of entries. > + * > + * May be overridden by the architecture; otherwise, implemented as a simple > + * loop over ptep_modify_prot_commit(). > + * > + * Context: The caller holds the page table lock. The PTEs are all in the same > + * PMD. On exit, the set ptes in the batch map the same folio. The ptes set by > + * ptep_modify_prot_start() may additionally have young and/or dirty bits set > + * where previously they were not, so the updated ptes may have these > + * additional changes. > + */ > +#ifndef modify_prot_commit_ptes > +static inline void modify_prot_commit_ptes(struct vm_area_struct *vma, unsigned long addr, > + pte_t *ptep, pte_t old_pte, pte_t pte, unsigned int nr) > +{ > + int i; > + > + for (i = 0; i < nr; ++i, ++ptep, addr += PAGE_SIZE) { > + ptep_modify_prot_commit(vma, addr, ptep, old_pte, pte); > + > + /* Advance PFN only, set same prot */ > + old_pte = pte_next_pfn(old_pte); > + pte = pte_next_pfn(pte); > + } > +} > +#endif > + > #endif /* CONFIG_MMU */ > > /* > diff --git a/mm/mprotect.c b/mm/mprotect.c > index 97adc62c50ab..4977f198168e 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -204,7 +204,7 @@ static long change_pte_range(struct mmu_gather *tlb, > } > } > > - oldpte = ptep_modify_prot_start(vma, addr, pte); > + oldpte = modify_prot_start_ptes(vma, addr, pte, nr_ptes); > ptent = pte_modify(oldpte, newprot); > > if (uffd_wp) > @@ -230,7 +230,7 @@ static long change_pte_range(struct mmu_gather *tlb, > can_change_pte_writable(vma, addr, ptent)) > ptent = pte_mkwrite(ptent, vma); > > - ptep_modify_prot_commit(vma, addr, pte, oldpte, ptent); > + modify_prot_commit_ptes(vma, addr, pte, oldpte, ptent, nr_ptes); > if (pte_needs_flush(oldpte, ptent)) > tlb_flush_pte_range(tlb, addr, PAGE_SIZE); > pages++;