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Mon, 11 Mar 2019 16:10:21 -0700 (PDT) Date: Mon, 11 Mar 2019 17:10:17 -0600 From: Yu Zhao To: Anshuman Khandual 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-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190311_161026_310753_C3AEBC51 X-CRM114-Status: GOOD ( 24.85 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , linux-arch@vger.kernel.org, Ard Biesheuvel , Peter Zijlstra , Catalin Marinas , Will Deacon , linux-kernel@vger.kernel.org, Nick Piggin , Jun Yao , linux-mm@kvack.org, "Aneesh Kumar K . V" , Chintan Pandya , Joel Fernandes , "Kirill A . Shutemov" , Andrew Morton , Laura Abbott , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.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. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel