Messages in this thread | | | Date | Tue, 22 Nov 2022 17:57:50 +0100 | Subject | Re: [PATCH] mm: introduce arch_has_hw_pmd_young() | From | Sander Eikelenboom <> |
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On 21/11/2022 10:50, Juergen Gross wrote: > On 21.11.22 10:32, Juergen Gross wrote: >> When running as a Xen PV guests commit eed9a328aa1a ("mm: x86: add >> CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG") can cause a protection violation >> in pmdp_test_and_clear_young(): >> >> BUG: unable to handle page fault for address: ffff8880083374d0 >> #PF: supervisor write access in kernel mode >> #PF: error_code(0x0003) - permissions violation >> PGD 3026067 P4D 3026067 PUD 3027067 PMD 7fee5067 PTE 8010000008337065 >> Oops: 0003 [#1] PREEMPT SMP NOPTI >> CPU: 7 PID: 158 Comm: kswapd0 Not tainted 6.1.0-rc5-20221118-doflr+ #1 >> RIP: e030:pmdp_test_and_clear_young+0x25/0x40 >> >> This happens because the Xen hypervisor can't emulate direct writes to >> page table entries other than PTEs. >> >> This can easily be fixed by introducing arch_has_hw_pmd_young() >> similar to arch_has_hw_pte_young() and test that instead of >> CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG. > > I just spotted that I missed to update my commit message to match the > patch: > > s/arch_has_hw_pmd_young/arch_has_hw_nonleaf_pmd_young/ > > I'll wait with a resend in order to get some feedback first. > > > Juergen
Hi Juergen,
Thanks for the patch, had it running overnight and did some kernel compiles. No crashes with this patch so far, so it seems to work for me.
-- Sander
>> >> Fixes: eed9a328aa1a ("mm: x86: add CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG") >> Reported-by: Sander Eikelenboom <linux@eikelenboom.it> >> Signed-off-by: Juergen Gross <jgross@suse.com> >> --- >> arch/x86/include/asm/pgtable.h | 8 ++++++++ >> include/linux/pgtable.h | 11 +++++++++++ >> mm/vmscan.c | 10 +++++----- >> 3 files changed, 24 insertions(+), 5 deletions(-) >> >> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h >> index 5059799bebe3..c567a6ed17ce 100644 >> --- a/arch/x86/include/asm/pgtable.h >> +++ b/arch/x86/include/asm/pgtable.h >> @@ -1438,6 +1438,14 @@ static inline bool arch_has_hw_pte_young(void) >> return true; >> } >> >> +#ifdef CONFIG_XEN_PV >> +#define arch_has_hw_nonleaf_pmd_young arch_has_hw_nonleaf_pmd_young >> +static inline bool arch_has_hw_nonleaf_pmd_young(void) >> +{ >> + return !cpu_feature_enabled(X86_FEATURE_XENPV); >> +} >> +#endif >> + >> #ifdef CONFIG_PAGE_TABLE_CHECK >> static inline bool pte_user_accessible_page(pte_t pte) >> { >> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h >> index a108b60a6962..58fc7e2d9575 100644 >> --- a/include/linux/pgtable.h >> +++ b/include/linux/pgtable.h >> @@ -260,6 +260,17 @@ static inline int pmdp_clear_flush_young(struct vm_area_struct *vma, >> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ >> #endif >> >> +#ifndef arch_has_hw_nonleaf_pmd_young >> +/* >> + * Return whether the accessed bit in non-leaf PMD entries is supported on the >> + * local CPU. >> + */ >> +static inline bool arch_has_hw_nonleaf_pmd_young(void) >> +{ >> + return IS_ENABLED(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG); >> +} >> +#endif >> + >> #ifndef arch_has_hw_pte_young >> /* >> * Return whether the accessed bit is supported on the local CPU. >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 04d8b88e5216..a04ac3b18326 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -3975,7 +3975,7 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long next, struct vm_area >> goto next; >> >> if (!pmd_trans_huge(pmd[i])) { >> - if (IS_ENABLED(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG) && >> + if (arch_has_hw_nonleaf_pmd_young() && >> get_cap(LRU_GEN_NONLEAF_YOUNG)) >> pmdp_test_and_clear_young(vma, addr, pmd + i); >> goto next; >> @@ -4073,14 +4073,14 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end, >> #endif >> walk->mm_stats[MM_NONLEAF_TOTAL]++; >> >> -#ifdef CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG >> - if (get_cap(LRU_GEN_NONLEAF_YOUNG)) { >> + if (arch_has_hw_nonleaf_pmd_young() && >> + get_cap(LRU_GEN_NONLEAF_YOUNG)) { >> if (!pmd_young(val)) >> continue; >> >> walk_pmd_range_locked(pud, addr, vma, args, bitmap, &pos); >> } >> -#endif >> + >> if (!walk->force_scan && !test_bloom_filter(walk->lruvec, walk->max_seq, pmd + i)) >> continue; >> >> @@ -5354,7 +5354,7 @@ static ssize_t show_enabled(struct kobject *kobj, struct kobj_attribute *attr, c >> if (arch_has_hw_pte_young() && get_cap(LRU_GEN_MM_WALK)) >> caps |= BIT(LRU_GEN_MM_WALK); >> >> - if (IS_ENABLED(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG) && get_cap(LRU_GEN_NONLEAF_YOUNG)) >> + if (arch_has_hw_nonleaf_pmd_young() && get_cap(LRU_GEN_NONLEAF_YOUNG)) >> caps |= BIT(LRU_GEN_NONLEAF_YOUNG); >> >> return snprintf(buf, PAGE_SIZE, "0x%04x\n", caps); >
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