arm64: Don't report clear pmds and puds as huge

commit fd28f5d439fca77348c129d5b73043a56f8a0296 upstream.

The current pmd_huge() and pud_huge() functions simply check if the table
bit is not set and reports the entries as huge in that case.  This is
counter-intuitive as a clear pmd/pud cannot also be a huge pmd/pud, and
it is inconsistent with at least arm and x86.

To prevent others from making the same mistake as me in looking at code
that calls these functions and to fix an issue with KVM on arm64 that
causes memory corruption due to incorrect page reference counting
resulting from this mistake, let's change the behavior.

Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Reviewed-by: Steve Capper <steve.capper@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Fixes: 084bd29810a5 ("ARM64: mm: HugeTLB support.")
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 023747bf4dd7dd2025a17c3fc44244aa1b0f7b00..e3a24b75e53c02130f580c7203681701afb6ce6b 100644 (file)
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -46,13 +46,13 @@ struct page *follow_huge_addr(struct mm_struct *mm, unsigned long address,
 
 int pmd_huge(pmd_t pmd)
 {
-       return !(pmd_val(pmd) & PMD_TABLE_BIT);
+       return pmd_val(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT);
 }
 
 int pud_huge(pud_t pud)
 {
 #ifndef __PAGETABLE_PMD_FOLDED
-       return !(pud_val(pud) & PUD_TABLE_BIT);
+       return pud_val(pud) && !(pud_val(pud) & PUD_TABLE_BIT);
 #else
        return 0;
 #endif