Messages in this thread | | | Subject | Re: [PATCH V2 2/2] mm/pgtable/debug: Add test validating architecture page table helpers | From | Christophe Leroy <> | Date | Wed, 18 Sep 2019 18:26:03 +0200 |
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Le 18/09/2019 à 07:04, Anshuman Khandual a écrit : > > > On 09/13/2019 03:31 PM, Christophe Leroy wrote: >> >> >> Le 13/09/2019 à 11:02, Anshuman Khandual a écrit : >>> >>>>> +#if !defined(__PAGETABLE_PMD_FOLDED) && !defined(__ARCH_HAS_4LEVEL_HACK) >>>> >>>> #ifdefs have to be avoided as much as possible, see below >>> >>> Yeah but it has been bit difficult to avoid all these $ifdef because of the >>> availability (or lack of it) for all these pgtable helpers in various config >>> combinations on all platforms. >> >> As far as I can see these pgtable helpers should exist everywhere at least via asm-generic/ files. > > But they might not actually do the right thing. > >> >> Can you spot a particular config which fails ? > > Lets consider the following example (after removing the $ifdefs around it) > which though builds successfully but fails to pass the intended test. This > is with arm64 config 4K pages sizes with 39 bits VA space which ends up > with a 3 level page table arrangement. > > static void __init p4d_clear_tests(p4d_t *p4dp) > { > p4d_t p4d = READ_ONCE(*p4dp);
My suggestion was not to completely drop the #ifdef but to do like you did in pgd_clear_tests() for instance, ie to add the following test on top of the function:
if (mm_pud_folded(mm) || is_defined(__ARCH_HAS_5LEVEL_HACK)) return;
> > p4d = __p4d(p4d_val(p4d) | RANDOM_ORVALUE); > WRITE_ONCE(*p4dp, p4d); > p4d_clear(p4dp); > p4d = READ_ONCE(*p4dp); > WARN_ON(!p4d_none(p4d)); > } > > The following test hits an error at WARN_ON(!p4d_none(p4d)) > > [ 16.757333] ------------[ cut here ]------------ > [ 16.758019] WARNING: CPU: 11 PID: 1 at mm/arch_pgtable_test.c:187 arch_pgtable_tests_init+0x24c/0x474 > [ 16.759455] Modules linked in: > [ 16.759952] CPU: 11 PID: 1 Comm: swapper/0 Not tainted 5.3.0-next-20190916-00005-g61c218153bb8-dirty #222 > [ 16.761449] Hardware name: linux,dummy-virt (DT) > [ 16.762185] pstate: 00400005 (nzcv daif +PAN -UAO) > [ 16.762964] pc : arch_pgtable_tests_init+0x24c/0x474 > [ 16.763750] lr : arch_pgtable_tests_init+0x174/0x474 > [ 16.764534] sp : ffffffc011d7bd50 > [ 16.765065] x29: ffffffc011d7bd50 x28: ffffffff1756bac0 > [ 16.765908] x27: ffffff85ddaf3000 x26: 00000000000002e8 > [ 16.766767] x25: ffffffc0111ce000 x24: ffffff85ddaf32e8 > [ 16.767606] x23: ffffff85ddaef278 x22: 00000045cc844000 > [ 16.768445] x21: 000000065daef003 x20: ffffffff17540000 > [ 16.769283] x19: ffffff85ddb60000 x18: 0000000000000014 > [ 16.770122] x17: 00000000980426bb x16: 00000000698594c6 > [ 16.770976] x15: 0000000066e25a88 x14: 0000000000000000 > [ 16.771813] x13: ffffffff17540000 x12: 000000000000000a > [ 16.772651] x11: ffffff85fcfd0a40 x10: 0000000000000001 > [ 16.773488] x9 : 0000000000000008 x8 : ffffffc01143ab26 > [ 16.774336] x7 : 0000000000000000 x6 : 0000000000000000 > [ 16.775180] x5 : 0000000000000000 x4 : 0000000000000000 > [ 16.776018] x3 : ffffffff1756bbe8 x2 : 000000065daeb003 > [ 16.776856] x1 : 000000000065daeb x0 : fffffffffffff000 > [ 16.777693] Call trace: > [ 16.778092] arch_pgtable_tests_init+0x24c/0x474 > [ 16.778843] do_one_initcall+0x74/0x1b0 > [ 16.779458] kernel_init_freeable+0x1cc/0x290 > [ 16.780151] kernel_init+0x10/0x100 > [ 16.780710] ret_from_fork+0x10/0x18 > [ 16.781282] ---[ end trace 042e6c40c0a3b038 ]--- > > On arm64 (4K page size|39 bits VA|3 level page table) > > #elif CONFIG_PGTABLE_LEVELS == 3 /* Applicable here */ > #define __ARCH_USE_5LEVEL_HACK > #include <asm-generic/pgtable-nopud.h> > > Which pulls in > > #include <asm-generic/pgtable-nop4d-hack.h> > > which pulls in > > #include <asm-generic/5level-fixup.h> > > which defines > > static inline int p4d_none(p4d_t p4d) > { > return 0; > } > > which will invariably trigger WARN_ON(!p4d_none(p4d)). > > Similarly for next test p4d_populate_tests() which will always be > successful because p4d_bad() invariably returns negative. > > static inline int p4d_bad(p4d_t p4d) > { > return 0; > } > > static void __init p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp, > pud_t *pudp) > { > p4d_t p4d; > > /* > * This entry points to next level page table page. > * Hence this must not qualify as p4d_bad(). > */ > pud_clear(pudp); > p4d_clear(p4dp); > p4d_populate(mm, p4dp, pudp); > p4d = READ_ONCE(*p4dp); > WARN_ON(p4d_bad(p4d)); > } > > We should not run these tests for the above config because they are > not applicable and will invariably produce same result. > >> >>> >>>> >> >> [...] >> >>>>> +#if !defined(__PAGETABLE_PUD_FOLDED) && !defined(__ARCH_HAS_5LEVEL_HACK) >>>> >>>> The same can be done here. >>> >>> IIRC not only the page table helpers but there are data types (pxx_t) which >>> were not present on various configs and these wrappers help prevent build >>> failures. Any ways will try and see if this can be improved further. But >>> meanwhile if you have some suggestions, please do let me know. >> >> pgt_t and pmd_t are everywhere I guess. >> then pud_t and p4d_t have fallbacks in asm-generic files. > > Lets take another example where it fails to compile. On arm64 with 16K > page size, 48 bits VA, 4 level page table arrangement in the following > test, pgd_populate() does not have the required signature. > > static void pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp, p4d_t *p4dp) > { > pgd_t pgd; > > if (mm_p4d_folded(mm)) > return; > > /* > * This entry points to next level page table page. > * Hence this must not qualify as pgd_bad(). > */ > p4d_clear(p4dp); > pgd_clear(pgdp); > pgd_populate(mm, pgdp, p4dp); > pgd = READ_ONCE(*pgdp); > WARN_ON(pgd_bad(pgd)); > } > > mm/arch_pgtable_test.c: In function ‘pgd_populate_tests’: > mm/arch_pgtable_test.c:254:25: error: passing argument 3 of ‘pgd_populate’ from incompatible pointer type [-Werror=incompatible-pointer-types] > pgd_populate(mm, pgdp, p4dp); > ^~~~ > In file included from mm/arch_pgtable_test.c:27:0: > ./arch/arm64/include/asm/pgalloc.h:81:20: note: expected ‘pud_t * {aka struct <anonymous> *}’ but argument is of type ‘pgd_t * {aka struct <anonymous> *}’ > static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgdp, pud_t *pudp) > > The build failure is because p4d_t * maps to pgd_t * but the applicable > (it does not fallback on generic ones) pgd_populate() expects a pud_t *. > > Except for archs which have 5 level page able, pgd_populate() always accepts > lower level page table pointers as the last argument as they dont have that > many levels. > > arch/x86/include/asm/pgalloc.h:static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgd, p4d_t *p4d) > arch/s390/include/asm/pgalloc.h:static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgd, p4d_t *p4d) > > But others > > arch/arm64/include/asm/pgalloc.h:static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgdp, pud_t *pudp) > arch/m68k/include/asm/motorola_pgalloc.h:static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgd, pmd_t *pmd) > arch/mips/include/asm/pgalloc.h:static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgd, pud_t *pud) > arch/powerpc/include/asm/book3s/64/pgalloc.h:static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgd, pud_t *pud) > > I remember going through all these combinations before arriving at the > current state of #ifdef exclusions. Probably, to solved this all platforms > have to define pxx_populate() helpers assuming they support 5 level page > table. > >> >> So it shouldn't be an issue. Maybe if a couple of arches miss them, the best would be to fix the arches, since that's the purpose of your testsuite isn't it ? > > The run time failures as explained previously is because of the folding which > needs to be protected as they are not even applicable. The compile time > failures are because pxx_populate() signatures are platform specific depending > on how many page table levels they really support. >
So IIUC, the compiletime problem is around __ARCH_HAS_5LEVEL_HACK. For all #if !defined(__PAGETABLE_PXX_FOLDED), something equivalent to the following should make the trick.
if (mm_pxx_folded()) return;
For the __ARCH_HAS_5LEVEL_HACK stuff, I think we should be able to regroup all impacted functions inside a single #ifdef __ARCH_HAS_5LEVEL_HACK
Christophe
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