arm/arm64: KVM: Implement Stage-2 page aging

Until now, KVM/arm didn't care much for page aging (who was swapping
anyway?), and simply provided empty hooks to the core KVM code. With
server-type systems now being available, things are quite different.

This patch implements very simple support for page aging, by clearing
the Access flag in the Stage-2 page tables. On access fault, the current
fault handling will write the PTE or PMD again, putting the Access flag
back on.

It should be possible to implement a much faster handling for Access
faults, but that's left for a later patch.

With this in place, performance in VMs is degraded much more gracefully.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

3 files changed, 4 insertions, 11 deletions

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index 92bbae381598..70522450ca23 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -90,6 +90,7 @@
 #define ESR_ELx_FSC             (0x3F)
 #define ESR_ELx_FSC_TYPE        (0x3C)
 #define ESR_ELx_FSC_EXTABT      (0x10)
+#define ESR_ELx_FSC_ACCESS      (0x08)
 #define ESR_ELx_FSC_FAULT       (0x04)
 #define ESR_ELx_FSC_PERM        (0x0C)
 #define ESR_ELx_CV              (UL(1) << 24)
diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
index 94674eb7e7bb..9e5543e08955 100644
--- a/arch/arm64/include/asm/kvm_arm.h
+++ b/arch/arm64/include/asm/kvm_arm.h
@@ -187,6 +187,7 @@
 
 /* For compatibility with fault code shared with 32-bit */
 #define FSC_FAULT       ESR_ELx_FSC_FAULT
+#define FSC_ACCESS      ESR_ELx_FSC_ACCESS
 #define FSC_PERM        ESR_ELx_FSC_PERM
 
 /* Hyp Prefetch Fault Address Register (HPFAR/HDFAR) */
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 967fb1cee300..f0f58c9beec0 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -179,19 +179,10 @@ int kvm_unmap_hva(struct kvm *kvm, unsigned long hva);
 int kvm_unmap_hva_range(struct kvm *kvm,
                         unsigned long start, unsigned long end);
 void kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte);
+int kvm_age_hva(struct kvm *kvm, unsigned long start, unsigned long end);
+int kvm_test_age_hva(struct kvm *kvm, unsigned long hva);
 
 /* We do not have shadow page tables, hence the empty hooks */
-static inline int kvm_age_hva(struct kvm *kvm, unsigned long start,
-                              unsigned long end)
-{
-        return 0;
-}
-
-static inline int kvm_test_age_hva(struct kvm *kvm, unsigned long hva)
-{
-        return 0;
-}
-
 static inline void kvm_arch_mmu_notifier_invalidate_page(struct kvm *kvm,
                                                          unsigned long address)
 {