From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yu Zhao Subject: Re: [PATCH v3 3/3] arm64: mm: enable per pmd page table lock Date: Mon, 11 Mar 2019 17:10:17 -0600 Message-ID: <20190311231017.GA207964@google.com> References: <20190218231319.178224-1-yuzhao@google.com> <20190310011906.254635-1-yuzhao@google.com> <20190310011906.254635-3-yuzhao@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Anshuman Khandual Cc: Catalin Marinas , Will Deacon , Mark Rutland , "Aneesh Kumar K . V" , Andrew Morton , Nick Piggin , Peter Zijlstra , Joel Fernandes , "Kirill A . Shutemov" , Ard Biesheuvel , Chintan Pandya , Jun Yao , Laura Abbott , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org List-Id: linux-arch.vger.kernel.org On Mon, Mar 11, 2019 at 01:58:27PM +0530, Anshuman Khandual wrote: > On 03/10/2019 06:49 AM, Yu Zhao wrote: > > Switch from per mm_struct to per pmd page table lock by enabling > > ARCH_ENABLE_SPLIT_PMD_PTLOCK. This provides better granularity for > > large system. > > > > I'm not sure if there is contention on mm->page_table_lock. Given > > the option comes at no cost (apart from initializing more spin > > locks), why not enable it now. > > > > We only do so when pmd is not folded, so we don't mistakenly call > > pgtable_pmd_page_ctor() on pud or p4d in pgd_pgtable_alloc(). (We > > check shift against PMD_SHIFT, which is same as PUD_SHIFT when pmd > > is folded). > > > > Signed-off-by: Yu Zhao > > --- > > arch/arm64/Kconfig | 3 +++ > > arch/arm64/include/asm/pgalloc.h | 12 +++++++++++- > > arch/arm64/include/asm/tlb.h | 5 ++++- > > 3 files changed, 18 insertions(+), 2 deletions(-) > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index cfbf307d6dc4..a3b1b789f766 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -872,6 +872,9 @@ config ARCH_WANT_HUGE_PMD_SHARE > > config ARCH_HAS_CACHE_LINE_SIZE > > def_bool y > > > > +config ARCH_ENABLE_SPLIT_PMD_PTLOCK > > + def_bool y if PGTABLE_LEVELS > 2 > > + > > config SECCOMP > > bool "Enable seccomp to safely compute untrusted bytecode" > > ---help--- > > diff --git a/arch/arm64/include/asm/pgalloc.h b/arch/arm64/include/asm/pgalloc.h > > index 52fa47c73bf0..dabba4b2c61f 100644 > > --- a/arch/arm64/include/asm/pgalloc.h > > +++ b/arch/arm64/include/asm/pgalloc.h > > @@ -33,12 +33,22 @@ > > > > static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long addr) > > { > > - return (pmd_t *)__get_free_page(PGALLOC_GFP); > > + struct page *page; > > + > > + page = alloc_page(PGALLOC_GFP); > > + if (!page) > > + return NULL; > > + if (!pgtable_pmd_page_ctor(page)) { > > + __free_page(page); > > + return NULL; > > + } > > + return page_address(page); > > } > > > > static inline void pmd_free(struct mm_struct *mm, pmd_t *pmdp) > > { > > BUG_ON((unsigned long)pmdp & (PAGE_SIZE-1)); > > + pgtable_pmd_page_dtor(virt_to_page(pmdp)); > > free_page((unsigned long)pmdp); > > } > > There is just one problem here. ARM KVM's stage2_pmd_free() calls into pmd_free() on a page > originally allocated with __get_free_page() and never went through pgtable_pmd_page_ctor(). > So when ARCH_ENABLE_SPLIT_PMD_PTLOCK is enabled > > stage2_pmd_free() > pgtable_pmd_page_dtor() > ptlock_free() > kmem_cache_free(page_ptl_cachep, page->ptl) > > Though SLUB implementation for kmem_cache_free() seems to be handling NULL page->ptl (as the > page never got it's lock allocated or initialized) correctly I am not sure if it is a right > thing to do. Thanks for reminding me. This should be fixed as well. Will do it in a separate patch. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it1-f196.google.com ([209.85.166.196]:51144 "EHLO mail-it1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726646AbfCKXKX (ORCPT ); Mon, 11 Mar 2019 19:10:23 -0400 Received: by mail-it1-f196.google.com with SMTP id m137so1445415ita.0 for ; Mon, 11 Mar 2019 16:10:22 -0700 (PDT) Date: Mon, 11 Mar 2019 17:10:17 -0600 From: Yu Zhao Subject: Re: [PATCH v3 3/3] arm64: mm: enable per pmd page table lock Message-ID: <20190311231017.GA207964@google.com> References: <20190218231319.178224-1-yuzhao@google.com> <20190310011906.254635-1-yuzhao@google.com> <20190310011906.254635-3-yuzhao@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Anshuman Khandual Cc: Catalin Marinas , Will Deacon , Mark Rutland , "Aneesh Kumar K . V" , Andrew Morton , Nick Piggin , Peter Zijlstra , Joel Fernandes , "Kirill A . Shutemov" , Ard Biesheuvel , Chintan Pandya , Jun Yao , Laura Abbott , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org Message-ID: <20190311231017.2hqgk9E7kDs1MhLOvikTFbvDMMfxyKfRXvRe1iI0SPM@z> On Mon, Mar 11, 2019 at 01:58:27PM +0530, Anshuman Khandual wrote: > On 03/10/2019 06:49 AM, Yu Zhao wrote: > > Switch from per mm_struct to per pmd page table lock by enabling > > ARCH_ENABLE_SPLIT_PMD_PTLOCK. This provides better granularity for > > large system. > > > > I'm not sure if there is contention on mm->page_table_lock. Given > > the option comes at no cost (apart from initializing more spin > > locks), why not enable it now. > > > > We only do so when pmd is not folded, so we don't mistakenly call > > pgtable_pmd_page_ctor() on pud or p4d in pgd_pgtable_alloc(). (We > > check shift against PMD_SHIFT, which is same as PUD_SHIFT when pmd > > is folded). > > > > Signed-off-by: Yu Zhao > > --- > > arch/arm64/Kconfig | 3 +++ > > arch/arm64/include/asm/pgalloc.h | 12 +++++++++++- > > arch/arm64/include/asm/tlb.h | 5 ++++- > > 3 files changed, 18 insertions(+), 2 deletions(-) > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index cfbf307d6dc4..a3b1b789f766 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -872,6 +872,9 @@ config ARCH_WANT_HUGE_PMD_SHARE > > config ARCH_HAS_CACHE_LINE_SIZE > > def_bool y > > > > +config ARCH_ENABLE_SPLIT_PMD_PTLOCK > > + def_bool y if PGTABLE_LEVELS > 2 > > + > > config SECCOMP > > bool "Enable seccomp to safely compute untrusted bytecode" > > ---help--- > > diff --git a/arch/arm64/include/asm/pgalloc.h b/arch/arm64/include/asm/pgalloc.h > > index 52fa47c73bf0..dabba4b2c61f 100644 > > --- a/arch/arm64/include/asm/pgalloc.h > > +++ b/arch/arm64/include/asm/pgalloc.h > > @@ -33,12 +33,22 @@ > > > > static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long addr) > > { > > - return (pmd_t *)__get_free_page(PGALLOC_GFP); > > + struct page *page; > > + > > + page = alloc_page(PGALLOC_GFP); > > + if (!page) > > + return NULL; > > + if (!pgtable_pmd_page_ctor(page)) { > > + __free_page(page); > > + return NULL; > > + } > > + return page_address(page); > > } > > > > static inline void pmd_free(struct mm_struct *mm, pmd_t *pmdp) > > { > > BUG_ON((unsigned long)pmdp & (PAGE_SIZE-1)); > > + pgtable_pmd_page_dtor(virt_to_page(pmdp)); > > free_page((unsigned long)pmdp); > > } > > There is just one problem here. ARM KVM's stage2_pmd_free() calls into pmd_free() on a page > originally allocated with __get_free_page() and never went through pgtable_pmd_page_ctor(). > So when ARCH_ENABLE_SPLIT_PMD_PTLOCK is enabled > > stage2_pmd_free() > pgtable_pmd_page_dtor() > ptlock_free() > kmem_cache_free(page_ptl_cachep, page->ptl) > > Though SLUB implementation for kmem_cache_free() seems to be handling NULL page->ptl (as the > page never got it's lock allocated or initialized) correctly I am not sure if it is a right > thing to do. Thanks for reminding me. This should be fixed as well. Will do it in a separate patch.