Messages in this thread | | | Subject | Re: [PATCH 1/1] mm/pgtable/debug: Add test validating architecture page table helpers | From | Christophe Leroy <> | Date | Tue, 10 Sep 2019 04:45:30 +0000 |
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On 09/10/2019 03:56 AM, Anshuman Khandual wrote: > > > On 09/09/2019 08:43 PM, Kirill A. Shutemov wrote: >> On Mon, Sep 09, 2019 at 11:56:50AM +0530, Anshuman Khandual wrote: >>> >>> >>> On 09/07/2019 12:33 AM, Gerald Schaefer wrote: >>>> On Fri, 6 Sep 2019 11:58:59 +0530 >>>> Anshuman Khandual <anshuman.khandual@arm.com> wrote: >>>> >>>>> On 09/05/2019 10:36 PM, Gerald Schaefer wrote: >>>>>> On Thu, 5 Sep 2019 14:48:14 +0530 >>>>>> Anshuman Khandual <anshuman.khandual@arm.com> wrote: >>>>>> >>>>>>>> [...] >>>>>>>>> + >>>>>>>>> +#if !defined(__PAGETABLE_PMD_FOLDED) && !defined(__ARCH_HAS_4LEVEL_HACK) >>>>>>>>> +static void pud_clear_tests(pud_t *pudp) >>>>>>>>> +{ >>>>>>>>> + memset(pudp, RANDOM_NZVALUE, sizeof(pud_t)); >>>>>>>>> + pud_clear(pudp); >>>>>>>>> + WARN_ON(!pud_none(READ_ONCE(*pudp))); >>>>>>>>> +} >>>>>>>> >>>>>>>> For pgd/p4d/pud_clear(), we only clear if the page table level is present >>>>>>>> and not folded. The memset() here overwrites the table type bits, so >>>>>>>> pud_clear() will not clear anything on s390 and the pud_none() check will >>>>>>>> fail. >>>>>>>> Would it be possible to OR a (larger) random value into the table, so that >>>>>>>> the lower 12 bits would be preserved? >>>>>>> >>>>>>> So the suggestion is instead of doing memset() on entry with RANDOM_NZVALUE, >>>>>>> it should OR a large random value preserving lower 12 bits. Hmm, this should >>>>>>> still do the trick for other platforms, they just need non zero value. So on >>>>>>> s390, the lower 12 bits on the page table entry already has valid value while >>>>>>> entering this function which would make sure that pud_clear() really does >>>>>>> clear the entry ? >>>>>> >>>>>> Yes, in theory the table entry on s390 would have the type set in the last >>>>>> 4 bits, so preserving those would be enough. If it does not conflict with >>>>>> others, I would still suggest preserving all 12 bits since those would contain >>>>>> arch-specific flags in general, just to be sure. For s390, the pte/pmd tests >>>>>> would also work with the memset, but for consistency I think the same logic >>>>>> should be used in all pxd_clear_tests. >>>>> >>>>> Makes sense but.. >>>>> >>>>> There is a small challenge with this. Modifying individual bits on a given >>>>> page table entry from generic code like this test case is bit tricky. That >>>>> is because there are not enough helpers to create entries with an absolute >>>>> value. This would have been easier if all the platforms provided functions >>>>> like __pxx() which is not the case now. Otherwise something like this should >>>>> have worked. >>>>> >>>>> >>>>> pud_t pud = READ_ONCE(*pudp); >>>>> pud = __pud(pud_val(pud) | RANDOM_VALUE (keeping lower 12 bits 0)) >>>>> WRITE_ONCE(*pudp, pud); >>>>> >>>>> But __pud() will fail to build in many platforms. >>>> >>>> Hmm, I simply used this on my system to make pud_clear_tests() work, not >>>> sure if it works on all archs: >>>> >>>> pud_val(*pudp) |= RANDOM_NZVALUE; >>> >>> Which compiles on arm64 but then fails on x86 because of the way pmd_val() >>> has been defined there. >> >> Use instead >> >> *pudp = __pud(pud_val(*pudp) | RANDOM_NZVALUE); > > Agreed. > > As I had mentioned before this would have been really the cleanest approach. > >> >> It *should* be more portable. > > Not really, because not all the platforms have __pxx() definitions right now. > Going with these will clearly cause build failures on affected platforms. Lets > examine __pud() for instance. It is defined only on these platforms. > > arch/arm64/include/asm/pgtable-types.h: #define __pud(x) ((pud_t) { (x) } ) > arch/mips/include/asm/pgtable-64.h: #define __pud(x) ((pud_t) { (x) }) > arch/powerpc/include/asm/pgtable-be-types.h: #define __pud(x) ((pud_t) { cpu_to_be64(x) }) > arch/powerpc/include/asm/pgtable-types.h: #define __pud(x) ((pud_t) { (x) }) > arch/s390/include/asm/page.h: #define __pud(x) ((pud_t) { (x) } ) > arch/sparc/include/asm/page_64.h: #define __pud(x) ((pud_t) { (x) } ) > arch/sparc/include/asm/page_64.h: #define __pud(x) (x) > arch/x86/include/asm/pgtable.h: #define __pud(x) native_make_pud(x)
You missed: arch/x86/include/asm/paravirt.h:static inline pud_t __pud(pudval_t val) include/asm-generic/pgtable-nop4d-hack.h:#define __pud(x) ((pud_t) { __pgd(x) }) include/asm-generic/pgtable-nopud.h:#define __pud(x) ((pud_t) { __p4d(x) })
> > Similarly for __pmd() > > arch/alpha/include/asm/page.h: #define __pmd(x) ((pmd_t) { (x) } ) > arch/arm/include/asm/page-nommu.h: #define __pmd(x) (x) > arch/arm/include/asm/pgtable-2level-types.h: #define __pmd(x) ((pmd_t) { (x) } ) > arch/arm/include/asm/pgtable-2level-types.h: #define __pmd(x) (x) > arch/arm/include/asm/pgtable-3level-types.h: #define __pmd(x) ((pmd_t) { (x) } ) > arch/arm/include/asm/pgtable-3level-types.h: #define __pmd(x) (x) > arch/arm64/include/asm/pgtable-types.h: #define __pmd(x) ((pmd_t) { (x) } ) > arch/m68k/include/asm/page.h: #define __pmd(x) ((pmd_t) { { (x) }, }) > arch/mips/include/asm/pgtable-64.h: #define __pmd(x) ((pmd_t) { (x) } ) > arch/nds32/include/asm/page.h: #define __pmd(x) (x) > arch/parisc/include/asm/page.h: #define __pmd(x) ((pmd_t) { (x) } ) > arch/parisc/include/asm/page.h: #define __pmd(x) (x) > arch/powerpc/include/asm/pgtable-be-types.h: #define __pmd(x) ((pmd_t) { cpu_to_be64(x) }) > arch/powerpc/include/asm/pgtable-types.h: #define __pmd(x) ((pmd_t) { (x) }) > arch/riscv/include/asm/pgtable-64.h: #define __pmd(x) ((pmd_t) { (x) }) > arch/s390/include/asm/page.h: #define __pmd(x) ((pmd_t) { (x) } ) > arch/sh/include/asm/pgtable-3level.h: #define __pmd(x) ((pmd_t) { (x) } ) > arch/sparc/include/asm/page_32.h: #define __pmd(x) ((pmd_t) { { (x) }, }) > arch/sparc/include/asm/page_32.h: #define __pmd(x) ((pmd_t) { { (x) }, }) > arch/sparc/include/asm/page_64.h: #define __pmd(x) ((pmd_t) { (x) } ) > arch/sparc/include/asm/page_64.h: #define __pmd(x) (x) > arch/um/include/asm/page.h: #define __pmd(x) ((pmd_t) { (x) } ) > arch/um/include/asm/page.h: #define __pmd(x) ((pmd_t) { (x) } ) > arch/x86/include/asm/pgtable.h: #define __pmd(x) native_make_pmd(x)
You missed: arch/x86/include/asm/paravirt.h:static inline pmd_t __pmd(pmdval_t val) include/asm-generic/page.h:#define __pmd(x) ((pmd_t) { (x) } ) include/asm-generic/pgtable-nopmd.h:#define __pmd(x) ((pmd_t) { __pud(x) } )
> > Similarly for __pgd() > > arch/alpha/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) } ) > arch/alpha/include/asm/page.h: #define __pgd(x) (x) > arch/arc/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) }) > arch/arc/include/asm/page.h: #define __pgd(x) (x) > arch/arm/include/asm/pgtable-3level-types.h: #define __pgd(x) ((pgd_t) { (x) } ) > arch/arm/include/asm/pgtable-3level-types.h: #define __pgd(x) (x) > arch/arm64/include/asm/pgtable-types.h: #define __pgd(x) ((pgd_t) { (x) } ) > arch/csky/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) }) > arch/hexagon/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) }) > arch/m68k/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) } ) > arch/mips/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) } ) > arch/nds32/include/asm/page.h: #define __pgd(x) (x) > arch/nios2/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) }) > arch/openrisc/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) }) > arch/parisc/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) } ) > arch/parisc/include/asm/page.h: #define __pgd(x) (x) > arch/powerpc/include/asm/pgtable-be-types.h: #define __pgd(x) ((pgd_t) { cpu_to_be64(x) }) > arch/powerpc/include/asm/pgtable-types.h: #define __pgd(x) ((pgd_t) { (x) }) > arch/riscv/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) }) > arch/s390/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) } ) > arch/sh/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) } ) > arch/sparc/include/asm/page_32.h: #define __pgd(x) ((pgd_t) { (x) } ) > arch/sparc/include/asm/page_32.h: #define __pgd(x) (x) > arch/sparc/include/asm/page_64.h: #define __pgd(x) ((pgd_t) { (x) } ) > arch/sparc/include/asm/page_64.h: #define __pgd(x) (x) > arch/um/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) } ) > arch/unicore32/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) }) > arch/unicore32/include/asm/page.h: #define __pgd(x) (x) > arch/x86/include/asm/pgtable.h: #define __pgd(x) native_make_pgd(x) > arch/xtensa/include/asm/page.h: #define __pgd(x) ((pgd_t) { (x) } )
You missed: arch/x86/include/asm/paravirt.h:static inline pgd_t __pgd(pgdval_t val) include/asm-generic/page.h:#define __pgd(x) ((pgd_t) { (x) } )
> > Similarly for __p4d() > > arch/s390/include/asm/page.h: #define __p4d(x) ((p4d_t) { (x) } ) > arch/x86/include/asm/pgtable.h: #define __p4d(x) native_make_p4d(x)
You missed: arch/x86/include/asm/paravirt.h:static inline p4d_t __p4d(p4dval_t val) include/asm-generic/5level-fixup.h:#define __p4d(x) __pgd(x) include/asm-generic/pgtable-nop4d.h:#define __p4d(x) ((p4d_t) { __pgd(x) })
> > The search pattern here has been "#define __pxx(". Unless I am missing something, > I dont see how we can use these without risking build failures. >
I guess you missed that arches not defining them fall back on the definitions in include/asm-generic
Christophe
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