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 87767C8302D for ; Mon, 30 Jun 2025 10:24:24 +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=odcu7nnUmXKebXvYQD8nU2XRX2NcefscWVOfflxgmrU=; b=bq72giHcXuoUTurkYSFFJzaMyX i0YcnWgCDh+45KN/l3vBDouFtlT4cClz5J4jMmIlUPzpgEAD75snuVAgWoTAmbCyuasaKzAf7sM8L ldl+vGbnC5s9nn0ulWExGfq7tsa3s+mXzRnQ/4i0dq4nRYPqpDfcPraKIMQXyYW9n3Ui+2ENIzr8e JIE3hS3qrlCQMzBr72igxwetMzRMmGvCI1yeBgkeVRAmO0Tx+qIGawOFdGeW9cTiqaY6rupYJ0di7 Fc6efjXMx+M6h6FKbkk5BRd/NNAAaXNb+IvhvfKtop65UBlCtbBxf9Tcc2nmEQPZV9obQXK7dz+ds hnJW0S+A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uWBgP-00000001sa0-29oN; Mon, 30 Jun 2025 10:24:17 +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 1uWBSz-00000001qNi-08rR for linux-arm-kernel@lists.infradead.org; Mon, 30 Jun 2025 10:10:26 +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 8A8F91D34; Mon, 30 Jun 2025 03:10:08 -0700 (PDT) Received: from [10.1.34.165] (XHFQ2J9959.cambridge.arm.com [10.1.34.165]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2E1573F58B; Mon, 30 Jun 2025 03:10:18 -0700 (PDT) Message-ID: <5f2eb53d-5fce-411f-857b-2ac16295a9f9@arm.com> Date: Mon, 30 Jun 2025 11:10:16 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/4] 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: <20250628113435.46678-1-dev.jain@arm.com> <20250628113435.46678-3-dev.jain@arm.com> From: Ryan Roberts In-Reply-To: <20250628113435.46678-3-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-20250630_031025_161071_EDA2FC53 X-CRM114-Status: GOOD ( 30.78 ) 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 28/06/2025 12:34, Dev Jain wrote: > Batch ptep_modify_prot_start/commit in preparation for optimizing mprotect. > Architecture can override these helpers; in case not, they are implemented > as a simple loop over the corresponding single pte helpers. > > Signed-off-by: Dev Jain > --- > include/linux/pgtable.h | 83 ++++++++++++++++++++++++++++++++++++++++- > mm/mprotect.c | 4 +- > 2 files changed, 84 insertions(+), 3 deletions(-) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index cf1515c163e2..662f39e7475a 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -1331,7 +1331,8 @@ 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 may have been "upgraded" w.r.t a/d bits compared > + * to the old_pte, as in, it may have a/d bits on which were off in old_pte. I find this last sentance a bit confusing. I think what you are trying to say is somehthing like: """ old_pte is the value returned from ptep_modify_prot_start() but may additionally have have young and/or dirty bits set where previously they were not. """ ? > */ > static inline void ptep_modify_prot_commit(struct vm_area_struct *vma, > unsigned long addr, > @@ -1340,6 +1341,86 @@ 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. The PTEs are all in the same PMD. > + * Since the batch is determined from folio_pte_batch, the PTEs must differ > + * only in a/d bits (and the soft dirty bit; see fpb_t flags in > + * mprotect_folio_pte_batch()). This last sentence is confusing... You had previous said the PFN can differ, but here you imply on a, d and sd bits are allowed to differ. > + */ > +#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 pte may have > + * been "upgraded" w.r.t a/d bits compared to the old_pte, as in, it may have > + * a/d bits on which were off in old_pte. Same comment as for ptep_modify_prot_start(). > + */ > +#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_modify_prot_commit(vma, addr, ptep, old_pte, pte); > + ptep++; > + addr += PAGE_SIZE; > + 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 af10a7fbe6b8..627b0d67cc4a 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -206,7 +206,7 @@ static long change_pte_range(struct mmu_gather *tlb, > continue; > } > > - oldpte = ptep_modify_prot_start(vma, addr, pte); > + oldpte = modify_prot_start_ptes(vma, addr, pte, nr_ptes); You're calling this with nr_ptes = 0 for the prot_numa case. But the implementation expects minimum nr_ptes == 1. > ptent = pte_modify(oldpte, newprot); > > if (uffd_wp) > @@ -232,7 +232,7 @@ 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++;