From e89ea813cc09ca7c31af81a87b4856cd3eba3ab9 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Mon, 21 Nov 2022 07:41:14 +0100 Subject: [PATCH] x86/mm: fix pmdp_test_and_clear_young() for Xen PV guests 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. In order to fix that do the PMD access bit resetting only when not running as a Xen PV guest. Note that PUD entries are no issue, as those won't be written directly by the kernel when running as a Xen PV guest due to transparent huge pages being disabled in that case. Fixes: eed9a328aa1a ("mm: x86: add CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG") Reported-by: Sander Eikelenboom Signed-off-by: Juergen Gross --- arch/x86/mm/pgtable.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c index 8525f2876fb4..076a99e77e28 100644 --- a/arch/x86/mm/pgtable.c +++ b/arch/x86/mm/pgtable.c @@ -556,9 +556,14 @@ int pmdp_test_and_clear_young(struct vm_area_struct *vma, { int ret = 0; - if (pmd_young(*pmdp)) - ret = test_and_clear_bit(_PAGE_BIT_ACCESSED, - (unsigned long *)pmdp); + if (pmd_young(*pmdp)) { + if (cpu_feature_enabled(X86_FEATURE_XENPV)) { + ret = 1; + } else { + ret = test_and_clear_bit(_PAGE_BIT_ACCESSED, + (unsigned long *)pmdp); + } + } return ret; } -- 2.35.3