From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anshuman Khandual Date: Fri, 06 Sep 2019 07:15:14 +0000 Subject: Re: [PATCH 1/1] mm/pgtable/debug: Add test validating architecture page table helpers Message-Id: <9c226f84-fe8f-8438-b378-b6659cccfcd1@arm.com> List-Id: References: <1567497706-8649-1-git-send-email-anshuman.khandual@arm.com> <1567497706-8649-2-git-send-email-anshuman.khandual@arm.com> <20190904141950.ykoe3h7b4hcvnysu@box> <6d4b989d-8eaa-d26e-6068-4b0e4d7a52f9@arm.com> <20190905085910.i6dppgnqi4ple22w@box.shutemov.name> In-Reply-To: <20190905085910.i6dppgnqi4ple22w@box.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: "Kirill A. Shutemov" Cc: Mark Rutland , linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Peter Zijlstra , James Hogan , Tetsuo Handa , Heiko Carstens , Michal Hocko , linux-mm@kvack.org, Dave Hansen , Paul Mackerras , sparclinux@vger.kernel.org, Thomas Gleixner , linux-s390@vger.kernel.org, Michael Ellerman , x86@kernel.org, Russell King - ARM Linux , Matthew Wilcox , Steven Price , Jason Gunthorpe , linux-arm-kernel@lists.infradead.org, linux-snps-arc@lists.infradead.org, Kees Cook , Masahiro Yamada , Mark Brown , Dan Williams , Vlastimil Babka , Sri Krishna chowdary , Ard Biesheuvel , Greg Kroah-Hartman , linux-mips@vger.kernel.org, Ralf Baechle , linux-kernel@vger.kernel.org, Paul Burton , Mike Rapoport , Vineet Gupta , Martin Schwidefsky , Andrew Morton , linuxppc-dev@lists.ozlabs.org, "David S. Miller" On 09/05/2019 02:29 PM, Kirill A. Shutemov wrote: > On Thu, Sep 05, 2019 at 01:48:27PM +0530, Anshuman Khandual wrote: >>>> +#define VADDR_TEST (PGDIR_SIZE + PUD_SIZE + PMD_SIZE + PAGE_SIZE) >>> >>> What is special about this address? How do you know if it is not occupied >>> yet? >> >> We are creating the page table from scratch after allocating an mm_struct >> for a given random virtual address 'VADDR_TEST'. Hence nothing is occupied >> just yet. There is nothing special about this address, just that it tries >> to ensure the page table entries are being created with some offset from >> beginning of respective page table page at all levels ? The idea is to >> have a more representative form of page table structure for test. > > Why P4D_SIZE is missing? That was an omission even though I was wondering whether it will be applicable or even make sense on platforms which dont have real P4D. > > Are you sure it will not land into kernel address space on any arch? Can it even cross user virtual address range with just a single span at each page table level ? TBH I did not think about that possibility. > > I think more robust way to deal with this would be using > get_unmapped_area() instead of fixed address. Makes sense and probably its better to get a virtual address which is known to have been checked against all boundary conditions. Will explore around get_unmapped_area() in this regard. > >> This makes sense for runtime cases but there is a problem here. >> >> On arm64, pgd_populate() which takes (pud_t *) as last argument instead of >> (p4d_t *) will fail to build when not wrapped in !__PAGETABLE_P4D_FOLDED >> on certain configurations. >> >> ./arch/arm64/include/asm/pgalloc.h:81:75: note: >> expected ‘pud_t *’ {aka ‘struct *’} >> but argument is of type ‘pgd_t *’ {aka ‘struct *’} >> static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgdp, pud_t *pudp) >> ~~~~~~~^~~~ >> Wondering if this is something to be fixed on arm64 or its more general >> problem. Will look into this further. > > I think you need wrap this into #ifndef __ARCH_HAS_5LEVEL_HACK. Okay. > >>>> + pmd_populate_tests(mm, pmdp, (pgtable_t) page); >>> >>> This is not correct for architectures that defines pgtable_t as pte_t >>> pointer, not struct page pointer. >> >> Right, a grep on the source confirms that. >> >> These platforms define pgtable_t as struct page * >> >> arch/alpha/include/asm/page.h:typedef struct page *pgtable_t; >> arch/arm/include/asm/page.h:typedef struct page *pgtable_t; >> arch/arm64/include/asm/page.h:typedef struct page *pgtable_t; >> arch/csky/include/asm/page.h:typedef struct page *pgtable_t; >> arch/hexagon/include/asm/page.h:typedef struct page *pgtable_t; >> arch/ia64/include/asm/page.h: typedef struct page *pgtable_t; >> arch/ia64/include/asm/page.h: typedef struct page *pgtable_t; >> arch/m68k/include/asm/page.h:typedef struct page *pgtable_t; >> arch/microblaze/include/asm/page.h:typedef struct page *pgtable_t; >> arch/mips/include/asm/page.h:typedef struct page *pgtable_t; >> arch/nds32/include/asm/page.h:typedef struct page *pgtable_t; >> arch/nios2/include/asm/page.h:typedef struct page *pgtable_t; >> arch/openrisc/include/asm/page.h:typedef struct page *pgtable_t; >> arch/parisc/include/asm/page.h:typedef struct page *pgtable_t; >> arch/riscv/include/asm/page.h:typedef struct page *pgtable_t; >> arch/sh/include/asm/page.h:typedef struct page *pgtable_t; >> arch/sparc/include/asm/page_32.h:typedef struct page *pgtable_t; >> arch/um/include/asm/page.h:typedef struct page *pgtable_t; >> arch/unicore32/include/asm/page.h:typedef struct page *pgtable_t; >> arch/x86/include/asm/pgtable_types.h:typedef struct page *pgtable_t; >> arch/xtensa/include/asm/page.h:typedef struct page *pgtable_t; >> >> These platforms define pgtable_t as pte_t * >> >> arch/arc/include/asm/page.h:typedef pte_t * pgtable_t; >> arch/powerpc/include/asm/mmu.h:typedef pte_t *pgtable_t; >> arch/s390/include/asm/page.h:typedef pte_t *pgtable_t; >> arch/sparc/include/asm/page_64.h:typedef pte_t *pgtable_t; >> >> Should we need have two pmd_populate_tests() definitions with >> different arguments (struct page pointer or pte_t pointer) and then >> call either one after detecting the given platform ? > > Use pte_alloc_one() instead of alloc_mapped_page() to allocate the page > table. Right, the PTE page table page should come from pte_alloc_one() instead directly from a struct page. The functions pte_alloc_one() and pte_free() operate on (struct page or pte_t) pointers depending applicable pgtable_t definition (in cases where platform defines otherwise). Will fix it. > >>>> + pud_populate_tests(mm, pudp, pmdp); >>>> + p4d_populate_tests(mm, p4dp, pudp); >>>> + pgd_populate_tests(mm, pgdp, p4dp); >>> >>> This is wrong. All p?dp points to the second entry in page table entry. >>> This is not valid pointer for page table and triggers p?d_bad() on x86. >> >> Yeah these are second entries because of the way we create the page table. >> But I guess its applicable only to the second argument in all these above >> cases because the first argument can be any valid entry on previous page >> table level. > > Yes: > > @@ -397,9 +396,9 @@ static int __init arch_pgtable_tests_init(void) > pgd_clear_tests(pgdp); > > pmd_populate_tests(mm, pmdp, (pgtable_t) page); > - pud_populate_tests(mm, pudp, pmdp); > - p4d_populate_tests(mm, p4dp, pudp); > - pgd_populate_tests(mm, pgdp, p4dp); > + pud_populate_tests(mm, pudp, saved_pmdp); > + p4d_populate_tests(mm, p4dp, saved_pudp); > + pgd_populate_tests(mm, pgdp, saved_p4dp); Sure.