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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id s139sm6748558qke.70.2020.03.02.11.40.42 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 02 Mar 2020 11:40:46 -0800 (PST) Message-ID: <1583178042.7365.146.camel@lca.pw> Subject: Re: [PATCH V14] mm/debug: Add tests validating architecture page table helpers From: Qian Cai To: Christophe Leroy , Anshuman Khandual , linux-mm@kvack.org Cc: Andrew Morton , Mike Rapoport , Vineet Gupta , Catalin Marinas , Will Deacon , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , "Kirill A . Shutemov" , Paul Walmsley , Palmer Dabbelt , linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-riscv@lists.infradead.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org Date: Mon, 02 Mar 2020 14:40:42 -0500 In-Reply-To: <1582732318.7365.129.camel@lca.pw> References: <1581909460-19148-1-git-send-email-anshuman.khandual@arm.com> <1582726182.7365.123.camel@lca.pw> <7c707b7f-ce3d-993b-8042-44fdc1ed28bf@c-s.fr> <1582732318.7365.129.camel@lca.pw> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-10.el7) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2020-02-26 at 10:51 -0500, Qian Cai wrote: > On Wed, 2020-02-26 at 15:45 +0100, Christophe Leroy wrote: > > > > Le 26/02/2020 à 15:09, Qian Cai a écrit : > > > On Mon, 2020-02-17 at 08:47 +0530, Anshuman Khandual wrote: > > > > This adds tests which will validate architecture page table helpers and > > > > other accessors in their compliance with expected generic MM semantics. > > > > This will help various architectures in validating changes to existing > > > > page table helpers or addition of new ones. > > > > > > > > This test covers basic page table entry transformations including but not > > > > limited to old, young, dirty, clean, write, write protect etc at various > > > > level along with populating intermediate entries with next page table page > > > > and validating them. > > > > > > > > Test page table pages are allocated from system memory with required size > > > > and alignments. The mapped pfns at page table levels are derived from a > > > > real pfn representing a valid kernel text symbol. This test gets called > > > > inside kernel_init() right after async_synchronize_full(). > > > > > > > > This test gets built and run when CONFIG_DEBUG_VM_PGTABLE is selected. Any > > > > architecture, which is willing to subscribe this test will need to select > > > > ARCH_HAS_DEBUG_VM_PGTABLE. For now this is limited to arc, arm64, x86, s390 > > > > and ppc32 platforms where the test is known to build and run successfully. > > > > Going forward, other architectures too can subscribe the test after fixing > > > > any build or runtime problems with their page table helpers. Meanwhile for > > > > better platform coverage, the test can also be enabled with CONFIG_EXPERT > > > > even without ARCH_HAS_DEBUG_VM_PGTABLE. > > > > > > > > Folks interested in making sure that a given platform's page table helpers > > > > conform to expected generic MM semantics should enable the above config > > > > which will just trigger this test during boot. Any non conformity here will > > > > be reported as an warning which would need to be fixed. This test will help > > > > catch any changes to the agreed upon semantics expected from generic MM and > > > > enable platforms to accommodate it thereafter. > > > > > > How useful is this that straightly crash the powerpc? > > > > > > [   23.263425][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating > > > architecture page table helpers > > > [   23.263625][    T1] ------------[ cut here ]------------ > > > [   23.263649][    T1] kernel BUG at arch/powerpc/mm/pgtable.c:274! > > > > The problem on PPC64 is known and has to be investigated and fixed. > > It might be interesting to hear what powerpc64 maintainers would say about it > and if it is actually worth "fixing" in the arch code, but that BUG_ON() was > there since 2009 and had not been exposed until this patch comes alone? This patch below makes it works on powerpc64 in order to dodge the BUG_ON()s in assert_pte_locked() triggered by pte_clear_tests(). diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c index 96dd7d574cef..50b385233971 100644 --- a/mm/debug_vm_pgtable.c +++ b/mm/debug_vm_pgtable.c @@ -55,6 +55,8 @@  #define RANDOM_ORVALUE GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS)  #define RANDOM_NZVALUE GENMASK(7, 0)   +unsigned long vaddr; +  static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)  {   pte_t pte = pfn_pte(pfn, prot); @@ -256,7 +258,7 @@ static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep)     pte = __pte(pte_val(pte) | RANDOM_ORVALUE);   WRITE_ONCE(*ptep, pte); - pte_clear(mm, 0, ptep); + pte_clear(mm, vaddr, ptep);   pte = READ_ONCE(*ptep);   WARN_ON(!pte_none(pte));  } @@ -310,8 +312,9 @@ void __init debug_vm_pgtable(void)   pgtable_t saved_ptep;   pgprot_t prot;   phys_addr_t paddr; - unsigned long vaddr, pte_aligned, pmd_aligned; + unsigned long pte_aligned, pmd_aligned;   unsigned long pud_aligned, p4d_aligned, pgd_aligned; + spinlock_t *ptl;     pr_info("Validating architecture page table helpers\n");   prot = vm_get_page_prot(VMFLAGS); @@ -344,7 +347,7 @@ void __init debug_vm_pgtable(void)   p4dp = p4d_alloc(mm, pgdp, vaddr);   pudp = pud_alloc(mm, p4dp, vaddr);   pmdp = pmd_alloc(mm, pudp, vaddr); - ptep = pte_alloc_map(mm, pmdp, vaddr); + ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);     /*    * Save all the page table page addresses as the page table @@ -370,7 +373,7 @@ void __init debug_vm_pgtable(void)   p4d_clear_tests(mm, p4dp);   pgd_clear_tests(mm, pgdp);   - pte_unmap(ptep); + pte_unmap_unlock(ptep, ptl);     pmd_populate_tests(mm, pmdp, saved_ptep);   pud_populate_tests(mm, pudp, saved_pmdp);