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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DA65EEB64D9 for ; Tue, 4 Jul 2023 10:01:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231359AbjGDKBR (ORCPT ); Tue, 4 Jul 2023 06:01:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38930 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230471AbjGDKBN (ORCPT ); Tue, 4 Jul 2023 06:01:13 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id D7B91F1 for ; Tue, 4 Jul 2023 03:01:07 -0700 (PDT) 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 B8FF92F4; Tue, 4 Jul 2023 03:01:49 -0700 (PDT) Received: from [10.163.47.48] (unknown [10.163.47.48]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 853503F73F; Tue, 4 Jul 2023 03:01:03 -0700 (PDT) Message-ID: Date: Tue, 4 Jul 2023 15:31:00 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [RFC] arm64: properly define SOFT_DIRTY for arm64 Content-Language: en-US To: Nico Pache , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: aquini@redhat.com, Andrew Morton , Catalin Marinas , David Hildenbrand , Gerald Schaefer , Liu Shixin , Will Deacon , Yu Zhao References: <20230703135526.930004-1-npache@redhat.com> From: Anshuman Khandual In-Reply-To: <20230703135526.930004-1-npache@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Nico, On 7/3/23 19:25, Nico Pache wrote: > ARM64 has a soft-dirty bit (software dirty) but never properly defines > CONFIG_ARCH_HAS_SOFT_DIRTY or its necessary functions. This patch > introduces the ability to set/clear the soft dirty bit in a similar > manner as the other arches that utilize it. > > However, we must be careful... there are cases where the DBM bit is not > available and the software dirty bit plays a essential role in determining > whether or not a page is dirty. In these cases we must not allow the > user to clear the software dirty bit. We can test for these cases by > utilizing the arch_faults_on_old_pte() function which test the availability > of DBM. The current soft-dirty bit is a SW PTE bit i.e PTE_DIRTY, tracking PTE dirtiness in absence of HW DBM support, although both these tracking methods are very much intertwined. Current pte helpers like pte_dirty(), pte_mkdirty(), pte_mkclean(), and pte_wrrotect() etc operate both on HW and SW dirty tracking bits irrespective of whether DBM is supported or not. For soft dirty to work, we need a software PTE bit which sticks around on the PTE entry until user space (only) clears it and above PTE_DIRTY bit cannot be used for that purpose as it could be cleared in the kernel. static inline pte_t pte_mkclean(pte_t pte) { pte = clear_pte_bit(pte, __pgprot(PTE_DIRTY)); pte = set_pte_bit(pte, __pgprot(PTE_RDONLY)); return pte; } BTW arch_faults_on_old_pte() is no longer available mainline. - Anshuman > > Cc: Andrew Morton > Cc: Anshuman Khandual > Cc: Catalin Marinas > Cc: David Hildenbrand > Cc: Gerald Schaefer > Cc: Liu Shixin > Cc: Will Deacon > Cc: Yu Zhao > Signed-off-by: Nico Pache > --- > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/pgtable.h | 77 +++++++++++++++++++++++++++++++- > 2 files changed, 76 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 891ab530a665..4de491627f49 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -173,6 +173,7 @@ config ARM64 > select HAVE_ARCH_PREL32_RELOCATIONS > select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET > select HAVE_ARCH_SECCOMP_FILTER > + select HAVE_ARCH_SOFT_DIRTY > select HAVE_ARCH_STACKLEAK > select HAVE_ARCH_THREAD_STRUCT_WHITELIST > select HAVE_ARCH_TRACEHOOK > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 0bd18de9fd97..a0a15ffa2417 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -121,8 +121,9 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys) > }) > > #define pte_hw_dirty(pte) (pte_write(pte) && !(pte_val(pte) & PTE_RDONLY)) > -#define pte_sw_dirty(pte) (!!(pte_val(pte) & PTE_DIRTY)) > -#define pte_dirty(pte) (pte_sw_dirty(pte) || pte_hw_dirty(pte)) > +#define pte_soft_dirty(pte) (!!(pte_val(pte) & PTE_DIRTY)) > +#define pte_dirty(pte) (pte_soft_dirty(pte) || pte_hw_dirty(pte)) > +#define pte_swp_soft_dirty(pte) pte_soft_dirty(pte) > > #define pte_valid(pte) (!!(pte_val(pte) & PTE_VALID)) > /* > @@ -1096,6 +1097,78 @@ static inline bool pud_sect_supported(void) > return PAGE_SIZE == SZ_4K; > } > > +#ifdef CONFIG_ARM64_HW_AFDBM > +/* > + * if we have the DBM bit we can utilize the software dirty bit as > + * a mechanism to introduce the soft_dirty functionality; however, without > + * it this bit is crucial to determining if a entry is dirty and we cannot > + * clear it via software. DBM can also be disabled or broken on some early > + * armv8 devices, so check its availability before modifying it. > + */ > +static inline pte_t pte_clear_soft_dirty(pte_t pte) > +{ > + if (arch_faults_on_old_pte()) > + return pte; > + > + return clear_pte_bit(pte, __pgprot(PTE_DIRTY)); > +} > + > +static inline pte_t pte_mksoft_dirty(pte_t pte) > +{ > + if (arch_faults_on_old_pte()) > + return pte; > + > + return set_pte_bit(pte, __pgprot(PTE_DIRTY)); > +} > + > +static inline pte_t pte_swp_clear_soft_dirty(pte_t pte) > +{ > + if (arch_faults_on_old_pte()) > + return pte; > + > + return clear_pte_bit(pte, __pgprot(PTE_DIRTY)); > +} > + > +static inline pte_t pte_swp_mksoft_dirty(pte_t pte) > +{ > + if (arch_faults_on_old_pte()) > + return pte; > + > + return set_pte_bit(pte, __pgprot(PTE_DIRTY)); > +} > + > +static inline int pmd_soft_dirty(pmd_t pmd) > +{ > + return pte_soft_dirty(pmd_pte(pmd)); > +} > + > +static inline pmd_t pmd_clear_soft_dirty(pmd_t pmd) > +{ > + return pte_pmd(pte_clear_soft_dirty(pmd_pte(pmd))); > +} > + > +static inline pmd_t pmd_mksoft_dirty(pmd_t pmd) > +{ > + return pte_pmd(pte_mksoft_dirty(pmd_pte(pmd))); > +} > + > +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION > +static inline int pmd_swp_soft_dirty(pmd_t pmd) > +{ > + return pmd_soft_dirty(pmd); > +} > + > +static inline pmd_t pmd_swp_clear_soft_dirty(pmd_t pmd) > +{ > + return pmd_clear_soft_dirty(pmd); > +} > + > +static inline pmd_t pmd_swp_mksoft_dirty(pmd_t pmd) > +{ > + return pmd_mksoft_dirty(pmd); > +} > +#endif /* CONFIG_ARCH_ENABLE_THP_MIGRATION */ > +#endif /* CONFIG_ARM64_HW_AFDBM */ > > #define __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION > #define ptep_modify_prot_start ptep_modify_prot_start