Merge branch kvm-arm64/dirty-log-ordered into kvmarm-master/next

* kvm-arm64/dirty-log-ordered:
  : .
  : Retrofit some ordering into the existing API dirty-ring by:
  :
  : - relying on acquire/release semantics which are the default on x86,
  :   but need to be explicit on arm64
  :
  : - adding a new capability that indicate which flavor is supported, either
  :   with explicit ordering (arm64) or both implicit and explicit (x86),
  :   as suggested by Paolo at KVM Forum
  :
  : - documenting the requirements for this new capability on weakly ordered
  :   architectures
  :
  : - updating the selftests to do the right thing
  : .
  KVM: selftests: dirty-log: Use KVM_CAP_DIRTY_LOG_RING_ACQ_REL if available
  KVM: selftests: dirty-log: Upgrade flag accesses to acquire/release semantics
  KVM: Document weakly ordered architecture requirements for dirty ring
  KVM: x86: Select CONFIG_HAVE_KVM_DIRTY_RING_ACQ_REL
  KVM: Add KVM_CAP_DIRTY_LOG_RING_ACQ_REL capability and config option
  KVM: Use acquire/release semantics when accessing dirty ring GFN state

Signed-off-by: Marc Zyngier <maz@kernel.org>

2 files changed, 9 insertions, 4 deletions

diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
index 9c883c94d478..b5234d6efbe1 100644
--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -17,6 +17,7 @@
 #include <linux/bitmap.h>
 #include <linux/bitops.h>
 #include <linux/atomic.h>
+#include <asm/barrier.h>
 
 #include "kvm_util.h"
 #include "test_util.h"
@@ -264,7 +265,8 @@ static void default_after_vcpu_run(struct kvm_vcpu *vcpu, int ret, int err)
 
 static bool dirty_ring_supported(void)
 {
-	return kvm_has_cap(KVM_CAP_DIRTY_LOG_RING);
+	return (kvm_has_cap(KVM_CAP_DIRTY_LOG_RING) ||
+		kvm_has_cap(KVM_CAP_DIRTY_LOG_RING_ACQ_REL));
 }
 
 static void dirty_ring_create_vm_done(struct kvm_vm *vm)
@@ -279,12 +281,12 @@ static void dirty_ring_create_vm_done(struct kvm_vm *vm)
 
 static inline bool dirty_gfn_is_dirtied(struct kvm_dirty_gfn *gfn)
 {
-	return gfn->flags == KVM_DIRTY_GFN_F_DIRTY;
+	return smp_load_acquire(&gfn->flags) == KVM_DIRTY_GFN_F_DIRTY;
 }
 
 static inline void dirty_gfn_set_collected(struct kvm_dirty_gfn *gfn)
 {
-	gfn->flags = KVM_DIRTY_GFN_F_RESET;
+	smp_store_release(&gfn->flags, KVM_DIRTY_GFN_F_RESET);
 }
 
 static uint32_t dirty_ring_collect_one(struct kvm_dirty_gfn *dirty_gfns,
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 9889fe0d8919..411a4c0bc81c 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -82,7 +82,10 @@ unsigned int kvm_check_cap(long cap)
 
 void vm_enable_dirty_ring(struct kvm_vm *vm, uint32_t ring_size)
 {
-	vm_enable_cap(vm, KVM_CAP_DIRTY_LOG_RING, ring_size);
+	if (vm_check_cap(vm, KVM_CAP_DIRTY_LOG_RING_ACQ_REL))
+		vm_enable_cap(vm, KVM_CAP_DIRTY_LOG_RING_ACQ_REL, ring_size);
+	else
+		vm_enable_cap(vm, KVM_CAP_DIRTY_LOG_RING, ring_size);
 	vm->dirty_ring_size = ring_size;
 }