KVM: arm/arm64: Limit icache invalidation to prefetch aborts

We've so far eagerly invalidated the icache, no matter how
the page was faulted in (data or prefetch abort).

But we can easily track execution by setting the XN bits
in the S2 page tables, get the prefetch abort at HYP and
perform the icache invalidation at that time only.

As for most VMs, the instruction working set is pretty
small compared to the data set, this is likely to save
some traffic (specially as the invalidation is broadcast).

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, 12 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 56b3e03c85e7..1e1b20cb348f 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -173,6 +173,18 @@ static inline pmd_t kvm_s2pmd_mkwrite(pmd_t pmd)
 	return pmd;
 }
 
+static inline pte_t kvm_s2pte_mkexec(pte_t pte)
+{
+	pte_val(pte) &= ~PTE_S2_XN;
+	return pte;
+}
+
+static inline pmd_t kvm_s2pmd_mkexec(pmd_t pmd)
+{
+	pmd_val(pmd) &= ~PMD_S2_XN;
+	return pmd;
+}
+
 static inline void kvm_set_s2pte_readonly(pte_t *pte)
 {
 	pteval_t old_pteval, pteval;