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, 15 insertions, 4 deletions

diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index 2174244f6317..0417c8e2a81c 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -1292,7 +1292,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
                           unsigned long fault_status)
 {
         int ret;
-        bool write_fault, writable, hugetlb = false, force_pte = false;
+        bool write_fault, exec_fault, writable, hugetlb = false, force_pte = false;
         unsigned long mmu_seq;
         gfn_t gfn = fault_ipa >> PAGE_SHIFT;
         struct kvm *kvm = vcpu->kvm;
@@ -1304,7 +1304,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
         unsigned long flags = 0;
 
         write_fault = kvm_is_write_fault(vcpu);
-        if (fault_status == FSC_PERM && !write_fault) {
+        exec_fault = kvm_vcpu_trap_is_iabt(vcpu);
+        VM_BUG_ON(write_fault && exec_fault);
+
+        if (fault_status == FSC_PERM && !write_fault && !exec_fault) {
                 kvm_err("Unexpected L2 read permission error\n");
                 return -EFAULT;
         }
@@ -1398,7 +1401,11 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
                         kvm_set_pfn_dirty(pfn);
                 }
                 clean_dcache_guest_page(vcpu, pfn, PMD_SIZE);
-                invalidate_icache_guest_page(vcpu, pfn, PMD_SIZE);
+
+                if (exec_fault) {
+                        new_pmd = kvm_s2pmd_mkexec(new_pmd);
+                        invalidate_icache_guest_page(vcpu, pfn, PMD_SIZE);
+                }
 
                 ret = stage2_set_pmd_huge(kvm, memcache, fault_ipa, &new_pmd);
         } else {
@@ -1410,7 +1417,11 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
                         mark_page_dirty(kvm, gfn);
                 }
                 clean_dcache_guest_page(vcpu, pfn, PAGE_SIZE);
-                invalidate_icache_guest_page(vcpu, pfn, PAGE_SIZE);
+
+                if (exec_fault) {
+                        new_pte = kvm_s2pte_mkexec(new_pte);
+                        invalidate_icache_guest_page(vcpu, pfn, PAGE_SIZE);
+                }
 
                 ret = stage2_set_pte(kvm, memcache, fault_ipa, &new_pte, flags);
         }