KVM: Introduce KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2

The previous KVM_CAP_MANUAL_DIRTY_LOG_PROTECT has some problem which
blocks the correct usage from userspace.  Obsolete the old one and
introduce a new capability bit for it.
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Documentation/virtual/kvm/api.txt

@@ -330,7 +330,7 @@ They must be less than the value that KVM_CHECK_EXTENSION returns for
 the KVM_CAP_MULTI_ADDRESS_SPACE capability.
 
 The bits in the dirty bitmap are cleared before the ioctl returns, unless
-KVM_CAP_MANUAL_DIRTY_LOG_PROTECT is enabled.  For more information,
+KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is enabled.  For more information,
 see the description of the capability.
 
 4.9 KVM_SET_MEMORY_ALIAS
@@ -3791,7 +3791,7 @@ to I/O ports.
 
 4.117 KVM_CLEAR_DIRTY_LOG (vm ioctl)
 
-Capability: KVM_CAP_MANUAL_DIRTY_LOG_PROTECT
+Capability: KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2
 Architectures: x86
 Type: vm ioctl
 Parameters: struct kvm_dirty_log (in)
@@ -3824,10 +3824,10 @@ the address space for which you want to return the dirty bitmap.
 They must be less than the value that KVM_CHECK_EXTENSION returns for
 the KVM_CAP_MULTI_ADDRESS_SPACE capability.
 
-This ioctl is mostly useful when KVM_CAP_MANUAL_DIRTY_LOG_PROTECT
+This ioctl is mostly useful when KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2
 is enabled; for more information, see the description of the capability.
 However, it can always be used as long as KVM_CHECK_EXTENSION confirms
-that KVM_CAP_MANUAL_DIRTY_LOG_PROTECT is present.
+that KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is present.
 
 4.118 KVM_GET_SUPPORTED_HV_CPUID
 
@@ -4780,7 +4780,7 @@ and injected exceptions.
 * For the new DR6 bits, note that bit 16 is set iff the #DB exception
   will clear DR6.RTM.
 
-7.18 KVM_CAP_MANUAL_DIRTY_LOG_PROTECT
+7.18 KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2
 
 Architectures: all
 Parameters: args[0] whether feature should be enabled or not
@@ -4803,6 +4803,11 @@ while userspace can see false reports of dirty pages.  Manual reprotection
 helps reducing this time, improving guest performance and reducing the
 number of dirty log false positives.
 
+KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 was previously available under the name
+KVM_CAP_MANUAL_DIRTY_LOG_PROTECT, but the implementation had bugs that make
+it hard or impossible to use it correctly.  The availability of
+KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 signals that those bugs are fixed.
+Userspace should not try to use KVM_CAP_MANUAL_DIRTY_LOG_PROTECT.
 
 8. Other capabilities.
 ----------------------

include/uapi/linux/kvm.h

@@ -986,8 +986,9 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_HYPERV_ENLIGHTENED_VMCS 163
 #define KVM_CAP_EXCEPTION_PAYLOAD 164
 #define KVM_CAP_ARM_VM_IPA_SIZE 165
-#define KVM_CAP_MANUAL_DIRTY_LOG_PROTECT 166
+#define KVM_CAP_MANUAL_DIRTY_LOG_PROTECT 166 /* Obsolete */
 #define KVM_CAP_HYPERV_CPUID 167
+#define KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 168
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -1434,7 +1435,7 @@ struct kvm_enc_region {
 #define KVM_GET_NESTED_STATE         _IOWR(KVMIO, 0xbe, struct kvm_nested_state)
 #define KVM_SET_NESTED_STATE         _IOW(KVMIO,  0xbf, struct kvm_nested_state)
 
-/* Available with KVM_CAP_MANUAL_DIRTY_LOG_PROTECT */
+/* Available with KVM_CAP_MANUAL_DIRTY_LOG_PROTECT_2 */
 #define KVM_CLEAR_DIRTY_LOG          _IOWR(KVMIO, 0xc0, struct kvm_clear_dirty_log)
 
 /* Available with KVM_CAP_HYPERV_CPUID */

tools/testing/selftests/kvm/dirty_log_test.c

@@ -311,7 +311,7 @@ static void run_test(enum vm_guest_mode mode, unsigned long iterations,
 #ifdef USE_CLEAR_DIRTY_LOG
 	struct kvm_enable_cap cap = {};
 
-	cap.cap = KVM_CAP_MANUAL_DIRTY_LOG_PROTECT;
+	cap.cap = KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2;
 	cap.args[0] = 1;
 	vm_enable_cap(vm, &cap);
 #endif
@@ -427,7 +427,7 @@ int main(int argc, char *argv[])
 	int opt, i;
 
 #ifdef USE_CLEAR_DIRTY_LOG
-	if (!kvm_check_cap(KVM_CAP_MANUAL_DIRTY_LOG_PROTECT)) {
+	if (!kvm_check_cap(KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2)) {
 		fprintf(stderr, "KVM_CLEAR_DIRTY_LOG not available, skipping tests\n");
 		exit(KSFT_SKIP);
 	}

virt/kvm/kvm_main.c

@@ -3110,7 +3110,7 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 	case KVM_CAP_CHECK_EXTENSION_VM:
 	case KVM_CAP_ENABLE_CAP_VM:
 #ifdef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT
-	case KVM_CAP_MANUAL_DIRTY_LOG_PROTECT:
+	case KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2:
 #endif
 		return 1;
 #ifdef CONFIG_KVM_MMIO
@@ -3148,7 +3148,7 @@ static int kvm_vm_ioctl_enable_cap_generic(struct kvm *kvm,
 {
 	switch (cap->cap) {
 #ifdef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT
-	case KVM_CAP_MANUAL_DIRTY_LOG_PROTECT:
+	case KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2:
 		if (cap->flags || (cap->args[0] & ~1))
 			return -EINVAL;
 		kvm->manual_dirty_log_protect = cap->args[0];