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

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>

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 1e1b20c..126abef 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -203,6 +203,11 @@ static inline bool kvm_s2pte_readonly(pte_t *pte)
 	return (pte_val(*pte) & PTE_S2_RDWR) == PTE_S2_RDONLY;
 }
 
+static inline bool kvm_s2pte_exec(pte_t *pte)
+{
+	return !(pte_val(*pte) & PTE_S2_XN);
+}
+
 static inline void kvm_set_s2pmd_readonly(pmd_t *pmd)
 {
 	kvm_set_s2pte_readonly((pte_t *)pmd);
@@ -213,6 +218,11 @@ static inline bool kvm_s2pmd_readonly(pmd_t *pmd)
 	return kvm_s2pte_readonly((pte_t *)pmd);
 }
 
+static inline bool kvm_s2pmd_exec(pmd_t *pmd)
+{
+	return !(pmd_val(*pmd) & PMD_S2_XN);
+}
+
 static inline bool kvm_page_empty(void *ptr)
 {
 	struct page *ptr_page = virt_to_page(ptr);