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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (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 61241C4829E for ; Thu, 15 Feb 2024 11:32:00 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4TbCZl0xksz3dJ0 for ; Thu, 15 Feb 2024 22:31:59 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=arm.com (client-ip=217.140.110.172; helo=foss.arm.com; envelope-from=mark.rutland@arm.com; receiver=lists.ozlabs.org) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lists.ozlabs.org (Postfix) with ESMTP id 4TbCZH5NdNz2yNf for ; Thu, 15 Feb 2024 22:31:35 +1100 (AEDT) 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 A5D23DA7; Thu, 15 Feb 2024 03:31:44 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.68.11]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2BCF13F7B4; Thu, 15 Feb 2024 03:31:00 -0800 (PST) Date: Thu, 15 Feb 2024 11:30:56 +0000 From: Mark Rutland To: Ryan Roberts Subject: Re: [PATCH v6 18/18] arm64/mm: Automatically fold contpte mappings Message-ID: References: <20240215103205.2607016-1-ryan.roberts@arm.com> <20240215103205.2607016-19-ryan.roberts@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240215103205.2607016-19-ryan.roberts@arm.com> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kefeng Wang , x86@kernel.org, David Hildenbrand , Catalin Marinas , Yang Shi , Dave Hansen , linux-mm@kvack.org, Andrey Ryabinin , "H. Peter Anvin" , Will Deacon , Ard Biesheuvel , Marc Zyngier , Alistair Popple , Barry Song <21cnbao@gmail.com>, Matthew Wilcox , Ingo Molnar , Zi Yan , John Hubbard , Borislav Petkov , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, James Morse , Andrew Morton , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Feb 15, 2024 at 10:32:05AM +0000, Ryan Roberts wrote: > There are situations where a change to a single PTE could cause the > contpte block in which it resides to become foldable (i.e. could be > repainted with the contiguous bit). Such situations arise, for example, > when user space temporarily changes protections, via mprotect, for > individual pages, such can be the case for certain garbage collectors. > > We would like to detect when such a PTE change occurs. However this can > be expensive due to the amount of checking required. Therefore only > perform the checks when an indiviual PTE is modified via mprotect > (ptep_modify_prot_commit() -> set_pte_at() -> set_ptes(nr=1)) and only > when we are setting the final PTE in a contpte-aligned block. > > Signed-off-by: Ryan Roberts Acked-by: Mark Rutland Mark. > --- > arch/arm64/include/asm/pgtable.h | 26 +++++++++++++ > arch/arm64/mm/contpte.c | 64 ++++++++++++++++++++++++++++++++ > 2 files changed, 90 insertions(+) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 8310875133ff..401087e8a43d 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -1185,6 +1185,8 @@ extern void ptep_modify_prot_commit(struct vm_area_struct *vma, > * where it is possible and makes sense to do so. The PTE_CONT bit is considered > * a private implementation detail of the public ptep API (see below). > */ > +extern void __contpte_try_fold(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, pte_t pte); > extern void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr, > pte_t *ptep, pte_t pte); > extern pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte); > @@ -1206,6 +1208,29 @@ extern int contpte_ptep_set_access_flags(struct vm_area_struct *vma, > unsigned long addr, pte_t *ptep, > pte_t entry, int dirty); > > +static __always_inline void contpte_try_fold(struct mm_struct *mm, > + unsigned long addr, pte_t *ptep, pte_t pte) > +{ > + /* > + * Only bother trying if both the virtual and physical addresses are > + * aligned and correspond to the last entry in a contig range. The core > + * code mostly modifies ranges from low to high, so this is the likely > + * the last modification in the contig range, so a good time to fold. > + * We can't fold special mappings, because there is no associated folio. > + */ > + > + const unsigned long contmask = CONT_PTES - 1; > + bool valign = ((addr >> PAGE_SHIFT) & contmask) == contmask; > + > + if (unlikely(valign)) { > + bool palign = (pte_pfn(pte) & contmask) == contmask; > + > + if (unlikely(palign && > + pte_valid(pte) && !pte_cont(pte) && !pte_special(pte))) > + __contpte_try_fold(mm, addr, ptep, pte); > + } > +} > + > static __always_inline void contpte_try_unfold(struct mm_struct *mm, > unsigned long addr, pte_t *ptep, pte_t pte) > { > @@ -1286,6 +1311,7 @@ static __always_inline void set_ptes(struct mm_struct *mm, unsigned long addr, > if (likely(nr == 1)) { > contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep)); > __set_ptes(mm, addr, ptep, pte, 1); > + contpte_try_fold(mm, addr, ptep, pte); > } else { > contpte_set_ptes(mm, addr, ptep, pte, nr); > } > diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c > index 50e0173dc5ee..16788f07716d 100644 > --- a/arch/arm64/mm/contpte.c > +++ b/arch/arm64/mm/contpte.c > @@ -73,6 +73,70 @@ static void contpte_convert(struct mm_struct *mm, unsigned long addr, > __set_ptes(mm, start_addr, start_ptep, pte, CONT_PTES); > } > > +void __contpte_try_fold(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, pte_t pte) > +{ > + /* > + * We have already checked that the virtual and pysical addresses are > + * correctly aligned for a contpte mapping in contpte_try_fold() so the > + * remaining checks are to ensure that the contpte range is fully > + * covered by a single folio, and ensure that all the ptes are valid > + * with contiguous PFNs and matching prots. We ignore the state of the > + * access and dirty bits for the purpose of deciding if its a contiguous > + * range; the folding process will generate a single contpte entry which > + * has a single access and dirty bit. Those 2 bits are the logical OR of > + * their respective bits in the constituent pte entries. In order to > + * ensure the contpte range is covered by a single folio, we must > + * recover the folio from the pfn, but special mappings don't have a > + * folio backing them. Fortunately contpte_try_fold() already checked > + * that the pte is not special - we never try to fold special mappings. > + * Note we can't use vm_normal_page() for this since we don't have the > + * vma. > + */ > + > + unsigned long folio_start, folio_end; > + unsigned long cont_start, cont_end; > + pte_t expected_pte, subpte; > + struct folio *folio; > + struct page *page; > + unsigned long pfn; > + pte_t *orig_ptep; > + pgprot_t prot; > + > + int i; > + > + if (!mm_is_user(mm)) > + return; > + > + page = pte_page(pte); > + folio = page_folio(page); > + folio_start = addr - (page - &folio->page) * PAGE_SIZE; > + folio_end = folio_start + folio_nr_pages(folio) * PAGE_SIZE; > + cont_start = ALIGN_DOWN(addr, CONT_PTE_SIZE); > + cont_end = cont_start + CONT_PTE_SIZE; > + > + if (folio_start > cont_start || folio_end < cont_end) > + return; > + > + pfn = ALIGN_DOWN(pte_pfn(pte), CONT_PTES); > + prot = pte_pgprot(pte_mkold(pte_mkclean(pte))); > + expected_pte = pfn_pte(pfn, prot); > + orig_ptep = ptep; > + ptep = contpte_align_down(ptep); > + > + for (i = 0; i < CONT_PTES; i++) { > + subpte = pte_mkold(pte_mkclean(__ptep_get(ptep))); > + if (!pte_same(subpte, expected_pte)) > + return; > + expected_pte = pte_advance_pfn(expected_pte, 1); > + ptep++; > + } > + > + pte = pte_mkcont(pte); > + contpte_convert(mm, addr, orig_ptep, pte); > +} > +EXPORT_SYMBOL(__contpte_try_fold); > + > void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr, > pte_t *ptep, pte_t pte) > { > -- > 2.25.1 > 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 2A246C48BEB for ; Thu, 15 Feb 2024 11:31:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=rcVb+IAC1hiBMPx9MrP19zcZoF38DcP4PxXH8USSsqo=; b=tG7QVljkVqU/jf gMnkLIPbLk24x4Lqaw014LQ5dOyfcHeN6E200mFoyxyZS7BMJW3kTSu8gYF4YmT6xbrUdYn61fGE0 MYhqMzlLWkm5FakD+RLPRxQMu37PoI0vIUiP8fEky3kI+sqZnW2BS98AY8B3lonCUluwkW3lf5A1O fe1RGHEEhPXKcADPZoFZizAKRCdEqWsFwBoLRm6+oCSL9KuxrxnUfht3sglWIuNC7vM0CbqjF0iKc D6kSoIs3eoGJ65gHjbGqGwkHDcjETZs3eDM3ZYSyHt4382Xund/dRd0pSRFnRwo8jT3mFl/fam/ye ohN85wmvaZ0BLE/4022g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1raZxL-0000000G35n-2Iz0; Thu, 15 Feb 2024 11:31:07 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1raZxJ-0000000G33q-0hEQ for linux-arm-kernel@lists.infradead.org; Thu, 15 Feb 2024 11:31:06 +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 A5D23DA7; Thu, 15 Feb 2024 03:31:44 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.68.11]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2BCF13F7B4; Thu, 15 Feb 2024 03:31:00 -0800 (PST) Date: Thu, 15 Feb 2024 11:30:56 +0000 From: Mark Rutland To: Ryan Roberts Cc: Catalin Marinas , Will Deacon , Ard Biesheuvel , Marc Zyngier , James Morse , Andrey Ryabinin , Andrew Morton , Matthew Wilcox , David Hildenbrand , Kefeng Wang , John Hubbard , Zi Yan , Barry Song <21cnbao@gmail.com>, Alistair Popple , Yang Shi , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , linux-arm-kernel@lists.infradead.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 18/18] arm64/mm: Automatically fold contpte mappings Message-ID: References: <20240215103205.2607016-1-ryan.roberts@arm.com> <20240215103205.2607016-19-ryan.roberts@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20240215103205.2607016-19-ryan.roberts@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240215_033105_319239_19E249C7 X-CRM114-Status: GOOD ( 38.73 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Feb 15, 2024 at 10:32:05AM +0000, Ryan Roberts wrote: > There are situations where a change to a single PTE could cause the > contpte block in which it resides to become foldable (i.e. could be > repainted with the contiguous bit). Such situations arise, for example, > when user space temporarily changes protections, via mprotect, for > individual pages, such can be the case for certain garbage collectors. > > We would like to detect when such a PTE change occurs. However this can > be expensive due to the amount of checking required. Therefore only > perform the checks when an indiviual PTE is modified via mprotect > (ptep_modify_prot_commit() -> set_pte_at() -> set_ptes(nr=1)) and only > when we are setting the final PTE in a contpte-aligned block. > > Signed-off-by: Ryan Roberts Acked-by: Mark Rutland Mark. > --- > arch/arm64/include/asm/pgtable.h | 26 +++++++++++++ > arch/arm64/mm/contpte.c | 64 ++++++++++++++++++++++++++++++++ > 2 files changed, 90 insertions(+) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 8310875133ff..401087e8a43d 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -1185,6 +1185,8 @@ extern void ptep_modify_prot_commit(struct vm_area_struct *vma, > * where it is possible and makes sense to do so. The PTE_CONT bit is considered > * a private implementation detail of the public ptep API (see below). > */ > +extern void __contpte_try_fold(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, pte_t pte); > extern void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr, > pte_t *ptep, pte_t pte); > extern pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte); > @@ -1206,6 +1208,29 @@ extern int contpte_ptep_set_access_flags(struct vm_area_struct *vma, > unsigned long addr, pte_t *ptep, > pte_t entry, int dirty); > > +static __always_inline void contpte_try_fold(struct mm_struct *mm, > + unsigned long addr, pte_t *ptep, pte_t pte) > +{ > + /* > + * Only bother trying if both the virtual and physical addresses are > + * aligned and correspond to the last entry in a contig range. The core > + * code mostly modifies ranges from low to high, so this is the likely > + * the last modification in the contig range, so a good time to fold. > + * We can't fold special mappings, because there is no associated folio. > + */ > + > + const unsigned long contmask = CONT_PTES - 1; > + bool valign = ((addr >> PAGE_SHIFT) & contmask) == contmask; > + > + if (unlikely(valign)) { > + bool palign = (pte_pfn(pte) & contmask) == contmask; > + > + if (unlikely(palign && > + pte_valid(pte) && !pte_cont(pte) && !pte_special(pte))) > + __contpte_try_fold(mm, addr, ptep, pte); > + } > +} > + > static __always_inline void contpte_try_unfold(struct mm_struct *mm, > unsigned long addr, pte_t *ptep, pte_t pte) > { > @@ -1286,6 +1311,7 @@ static __always_inline void set_ptes(struct mm_struct *mm, unsigned long addr, > if (likely(nr == 1)) { > contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep)); > __set_ptes(mm, addr, ptep, pte, 1); > + contpte_try_fold(mm, addr, ptep, pte); > } else { > contpte_set_ptes(mm, addr, ptep, pte, nr); > } > diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c > index 50e0173dc5ee..16788f07716d 100644 > --- a/arch/arm64/mm/contpte.c > +++ b/arch/arm64/mm/contpte.c > @@ -73,6 +73,70 @@ static void contpte_convert(struct mm_struct *mm, unsigned long addr, > __set_ptes(mm, start_addr, start_ptep, pte, CONT_PTES); > } > > +void __contpte_try_fold(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, pte_t pte) > +{ > + /* > + * We have already checked that the virtual and pysical addresses are > + * correctly aligned for a contpte mapping in contpte_try_fold() so the > + * remaining checks are to ensure that the contpte range is fully > + * covered by a single folio, and ensure that all the ptes are valid > + * with contiguous PFNs and matching prots. We ignore the state of the > + * access and dirty bits for the purpose of deciding if its a contiguous > + * range; the folding process will generate a single contpte entry which > + * has a single access and dirty bit. Those 2 bits are the logical OR of > + * their respective bits in the constituent pte entries. In order to > + * ensure the contpte range is covered by a single folio, we must > + * recover the folio from the pfn, but special mappings don't have a > + * folio backing them. Fortunately contpte_try_fold() already checked > + * that the pte is not special - we never try to fold special mappings. > + * Note we can't use vm_normal_page() for this since we don't have the > + * vma. > + */ > + > + unsigned long folio_start, folio_end; > + unsigned long cont_start, cont_end; > + pte_t expected_pte, subpte; > + struct folio *folio; > + struct page *page; > + unsigned long pfn; > + pte_t *orig_ptep; > + pgprot_t prot; > + > + int i; > + > + if (!mm_is_user(mm)) > + return; > + > + page = pte_page(pte); > + folio = page_folio(page); > + folio_start = addr - (page - &folio->page) * PAGE_SIZE; > + folio_end = folio_start + folio_nr_pages(folio) * PAGE_SIZE; > + cont_start = ALIGN_DOWN(addr, CONT_PTE_SIZE); > + cont_end = cont_start + CONT_PTE_SIZE; > + > + if (folio_start > cont_start || folio_end < cont_end) > + return; > + > + pfn = ALIGN_DOWN(pte_pfn(pte), CONT_PTES); > + prot = pte_pgprot(pte_mkold(pte_mkclean(pte))); > + expected_pte = pfn_pte(pfn, prot); > + orig_ptep = ptep; > + ptep = contpte_align_down(ptep); > + > + for (i = 0; i < CONT_PTES; i++) { > + subpte = pte_mkold(pte_mkclean(__ptep_get(ptep))); > + if (!pte_same(subpte, expected_pte)) > + return; > + expected_pte = pte_advance_pfn(expected_pte, 1); > + ptep++; > + } > + > + pte = pte_mkcont(pte); > + contpte_convert(mm, addr, orig_ptep, pte); > +} > +EXPORT_SYMBOL(__contpte_try_fold); > + > void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr, > pte_t *ptep, pte_t pte) > { > -- > 2.25.1 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel 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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 04070C48BEB for ; Thu, 15 Feb 2024 11:31:07 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 8D93E8D0013; 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t=1707996664; a=rsa-sha256; cv=none; b=5v49813rUyyxsnVrCr9+tYqNBaNPHzHkTXC4qhOmG3tZmFCo93nOso+efVF0wJwzgdoP55 jzpTwO86uisBreYxyZlcBaEgXJj6sChInCySTiBlHLJT9bb3zu3lgJVBsqYBfxtk5Sv7RU yxF8fE2AzY7uS4JKqWxaF8zGgcislg0= 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 A5D23DA7; Thu, 15 Feb 2024 03:31:44 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.68.11]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2BCF13F7B4; Thu, 15 Feb 2024 03:31:00 -0800 (PST) Date: Thu, 15 Feb 2024 11:30:56 +0000 From: Mark Rutland To: Ryan Roberts Cc: Catalin Marinas , Will Deacon , Ard Biesheuvel , Marc Zyngier , James Morse , Andrey Ryabinin , Andrew Morton , Matthew Wilcox , David Hildenbrand , Kefeng Wang , John Hubbard , Zi Yan , Barry Song <21cnbao@gmail.com>, Alistair Popple , Yang Shi , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , linux-arm-kernel@lists.infradead.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 18/18] arm64/mm: Automatically fold contpte mappings Message-ID: References: <20240215103205.2607016-1-ryan.roberts@arm.com> <20240215103205.2607016-19-ryan.roberts@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240215103205.2607016-19-ryan.roberts@arm.com> X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9BC97A001E X-Stat-Signature: 1f9g6yy8jgbnkk8kfakb5hfat9mfzeaq X-HE-Tag: 1707996664-980344 X-HE-Meta: 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 8coxcDKg +M1Ngb1L9uFhGSN7j/5LVZfqUVHZKouN6yA5ga2v7VdSfPRdPc7YPbtOnNCrceTBRwVh6st4JMAQDf2SXt4BaHTrPhut2bBLLW2UlhdE2O0FtsnVGY83hAuKlmuU10eKniRdK9NKHO648YO5np4mPXZEZePgwEAnINXu4c+yGy2Wa0bV7Z1jzal4opF6otjZCsZ+zmAyNMNGOsHyVwqbY4IDz6MZcg4fTXE4CrJdC43cHy7Q= 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: On Thu, Feb 15, 2024 at 10:32:05AM +0000, Ryan Roberts wrote: > There are situations where a change to a single PTE could cause the > contpte block in which it resides to become foldable (i.e. could be > repainted with the contiguous bit). Such situations arise, for example, > when user space temporarily changes protections, via mprotect, for > individual pages, such can be the case for certain garbage collectors. > > We would like to detect when such a PTE change occurs. However this can > be expensive due to the amount of checking required. Therefore only > perform the checks when an indiviual PTE is modified via mprotect > (ptep_modify_prot_commit() -> set_pte_at() -> set_ptes(nr=1)) and only > when we are setting the final PTE in a contpte-aligned block. > > Signed-off-by: Ryan Roberts Acked-by: Mark Rutland Mark. > --- > arch/arm64/include/asm/pgtable.h | 26 +++++++++++++ > arch/arm64/mm/contpte.c | 64 ++++++++++++++++++++++++++++++++ > 2 files changed, 90 insertions(+) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 8310875133ff..401087e8a43d 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -1185,6 +1185,8 @@ extern void ptep_modify_prot_commit(struct vm_area_struct *vma, > * where it is possible and makes sense to do so. The PTE_CONT bit is considered > * a private implementation detail of the public ptep API (see below). > */ > +extern void __contpte_try_fold(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, pte_t pte); > extern void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr, > pte_t *ptep, pte_t pte); > extern pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte); > @@ -1206,6 +1208,29 @@ extern int contpte_ptep_set_access_flags(struct vm_area_struct *vma, > unsigned long addr, pte_t *ptep, > pte_t entry, int dirty); > > +static __always_inline void contpte_try_fold(struct mm_struct *mm, > + unsigned long addr, pte_t *ptep, pte_t pte) > +{ > + /* > + * Only bother trying if both the virtual and physical addresses are > + * aligned and correspond to the last entry in a contig range. The core > + * code mostly modifies ranges from low to high, so this is the likely > + * the last modification in the contig range, so a good time to fold. > + * We can't fold special mappings, because there is no associated folio. > + */ > + > + const unsigned long contmask = CONT_PTES - 1; > + bool valign = ((addr >> PAGE_SHIFT) & contmask) == contmask; > + > + if (unlikely(valign)) { > + bool palign = (pte_pfn(pte) & contmask) == contmask; > + > + if (unlikely(palign && > + pte_valid(pte) && !pte_cont(pte) && !pte_special(pte))) > + __contpte_try_fold(mm, addr, ptep, pte); > + } > +} > + > static __always_inline void contpte_try_unfold(struct mm_struct *mm, > unsigned long addr, pte_t *ptep, pte_t pte) > { > @@ -1286,6 +1311,7 @@ static __always_inline void set_ptes(struct mm_struct *mm, unsigned long addr, > if (likely(nr == 1)) { > contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep)); > __set_ptes(mm, addr, ptep, pte, 1); > + contpte_try_fold(mm, addr, ptep, pte); > } else { > contpte_set_ptes(mm, addr, ptep, pte, nr); > } > diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c > index 50e0173dc5ee..16788f07716d 100644 > --- a/arch/arm64/mm/contpte.c > +++ b/arch/arm64/mm/contpte.c > @@ -73,6 +73,70 @@ static void contpte_convert(struct mm_struct *mm, unsigned long addr, > __set_ptes(mm, start_addr, start_ptep, pte, CONT_PTES); > } > > +void __contpte_try_fold(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, pte_t pte) > +{ > + /* > + * We have already checked that the virtual and pysical addresses are > + * correctly aligned for a contpte mapping in contpte_try_fold() so the > + * remaining checks are to ensure that the contpte range is fully > + * covered by a single folio, and ensure that all the ptes are valid > + * with contiguous PFNs and matching prots. We ignore the state of the > + * access and dirty bits for the purpose of deciding if its a contiguous > + * range; the folding process will generate a single contpte entry which > + * has a single access and dirty bit. Those 2 bits are the logical OR of > + * their respective bits in the constituent pte entries. In order to > + * ensure the contpte range is covered by a single folio, we must > + * recover the folio from the pfn, but special mappings don't have a > + * folio backing them. Fortunately contpte_try_fold() already checked > + * that the pte is not special - we never try to fold special mappings. > + * Note we can't use vm_normal_page() for this since we don't have the > + * vma. > + */ > + > + unsigned long folio_start, folio_end; > + unsigned long cont_start, cont_end; > + pte_t expected_pte, subpte; > + struct folio *folio; > + struct page *page; > + unsigned long pfn; > + pte_t *orig_ptep; > + pgprot_t prot; > + > + int i; > + > + if (!mm_is_user(mm)) > + return; > + > + page = pte_page(pte); > + folio = page_folio(page); > + folio_start = addr - (page - &folio->page) * PAGE_SIZE; > + folio_end = folio_start + folio_nr_pages(folio) * PAGE_SIZE; > + cont_start = ALIGN_DOWN(addr, CONT_PTE_SIZE); > + cont_end = cont_start + CONT_PTE_SIZE; > + > + if (folio_start > cont_start || folio_end < cont_end) > + return; > + > + pfn = ALIGN_DOWN(pte_pfn(pte), CONT_PTES); > + prot = pte_pgprot(pte_mkold(pte_mkclean(pte))); > + expected_pte = pfn_pte(pfn, prot); > + orig_ptep = ptep; > + ptep = contpte_align_down(ptep); > + > + for (i = 0; i < CONT_PTES; i++) { > + subpte = pte_mkold(pte_mkclean(__ptep_get(ptep))); > + if (!pte_same(subpte, expected_pte)) > + return; > + expected_pte = pte_advance_pfn(expected_pte, 1); > + ptep++; > + } > + > + pte = pte_mkcont(pte); > + contpte_convert(mm, addr, orig_ptep, pte); > +} > +EXPORT_SYMBOL(__contpte_try_fold); > + > void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr, > pte_t *ptep, pte_t pte) > { > -- > 2.25.1 >