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Subject[PATCH] x86/mm: don't free p4d table when it is folded at runtime.
Date
When the p4d page table layer is folded at runtime, the p4d_free()
should do nothing, the same as in <asm-generic/pgtable-nop4d.h>.

It seems this bug should cause double-free in efi_call_phys_epilog(),
but I don't know how to trigger that code path, so I can't confirm that
by testing.

Fixes: 98219dda2ab5 ("x86/mm: Fold p4d page table layer at runtime")
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
arch/x86/include/asm/pgalloc.h | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/x86/include/asm/pgalloc.h b/arch/x86/include/asm/pgalloc.h
index ada6410fd2ec..fbd578daa66e 100644
--- a/arch/x86/include/asm/pgalloc.h
+++ b/arch/x86/include/asm/pgalloc.h
@@ -184,6 +184,9 @@ static inline p4d_t *p4d_alloc_one(struct mm_struct *mm, unsigned long addr)

static inline void p4d_free(struct mm_struct *mm, p4d_t *p4d)
{
+ if (!pgtable_l5_enabled())
+ return;
+
BUG_ON((unsigned long)p4d & (PAGE_SIZE-1));
free_page((unsigned long)p4d);
}
--
2.16.4
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