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KVM: arm/arm64: Preserve Exec permission across R/W permission faults

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So far, we loose the Exec property whenever we take permission
faults, as we always reconstruct the PTE/PMD from scratch. This
can be counter productive as we can end-up with the following
fault sequence:

	X -> RO -> ROX -> RW -> RWX

Instead, we can lookup the existing PTE/PMD and clear the XN bit in the
new entry if it was already cleared in the old one, leadig to a much
nicer fault sequence:

	X -> ROX -> RWX

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
This commit is contained in:
Marc Zyngier
2017-10-23 17:11:21 +01:00
committed by Christoffer Dall
parent a9c0e12ebe
commit 7a3796d2ef
3 changed files with 47 additions and 0 deletions
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10
arch/arm/include/asm/kvm_mmu.h
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@@ -107,6 +107,11 @@ static inline bool kvm_s2pte_readonly(pte_t *pte)
return (pte_val(*pte) & L_PTE_S2_RDWR) == L_PTE_S2_RDONLY;
}
static inline bool kvm_s2pte_exec(pte_t *pte)
{
return !(pte_val(*pte) & L_PTE_XN);
}
static inline void kvm_set_s2pmd_readonly(pmd_t *pmd)
{
pmd_val(*pmd) = (pmd_val(*pmd) & ~L_PMD_S2_RDWR) | L_PMD_S2_RDONLY;
@@ -117,6 +122,11 @@ static inline bool kvm_s2pmd_readonly(pmd_t *pmd)
return (pmd_val(*pmd) & L_PMD_S2_RDWR) == L_PMD_S2_RDONLY;
}
static inline bool kvm_s2pmd_exec(pmd_t *pmd)
{
return !(pmd_val(*pmd) & PMD_SECT_XN);
}
static inline bool kvm_page_empty(void *ptr)
{
struct page *ptr_page = virt_to_page(ptr);