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Subject: [PATCH RFC v7 02/64] KVM: x86: Add KVM_CAP_UNMAPPED_PRIVATE_MEMORY
Date:   Wed, 14 Dec 2022 13:39:54 -0600
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This mainly indicates to KVM that it should expect all private guest
memory to be backed by private memslots. Ideally this would work
similarly for others archs, give or take a few additional flags, but
for now it's a simple boolean indicator for x86.

Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 arch/x86/include/asm/kvm_host.h |  3 +++
 arch/x86/kvm/x86.c              | 10 ++++++++++
 include/uapi/linux/kvm.h        |  1 +
 3 files changed, 14 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 27ef31133352..2b6244525107 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1438,6 +1438,9 @@ struct kvm_arch {
 	 */
 #define SPLIT_DESC_CACHE_MIN_NR_OBJECTS (SPTE_ENT_PER_PAGE + 1)
 	struct kvm_mmu_memory_cache split_desc_cache;
+
+	/* Use/enforce unmapped private memory. */
+	bool upm_mode;
 };
 
 struct kvm_vm_stat {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c67e22f3e2ee..99ecf99bc4d2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4421,6 +4421,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_EXIT_HYPERCALL:
 		r = KVM_EXIT_HYPERCALL_VALID_MASK;
 		break;
+#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
+	case KVM_CAP_UNMAPPED_PRIVATE_MEM:
+		r = 1;
+		break;
+#endif
 	case KVM_CAP_SET_GUEST_DEBUG2:
 		return KVM_GUESTDBG_VALID_MASK;
 #ifdef CONFIG_KVM_XEN
@@ -6382,6 +6387,10 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		}
 		mutex_unlock(&kvm->lock);
 		break;
+	case KVM_CAP_UNMAPPED_PRIVATE_MEM:
+		kvm->arch.upm_mode = true;
+		r = 0;
+		break;
 	default:
 		r = -EINVAL;
 		break;
@@ -12128,6 +12137,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	kvm->arch.default_tsc_khz = max_tsc_khz ? : tsc_khz;
 	kvm->arch.guest_can_read_msr_platform_info = true;
 	kvm->arch.enable_pmu = enable_pmu;
+	kvm->arch.upm_mode = false;
 
 #if IS_ENABLED(CONFIG_HYPERV)
 	spin_lock_init(&kvm->arch.hv_root_tdp_lock);
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index c7e9d375a902..cc9424ccf9b2 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1219,6 +1219,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_DIRTY_LOG_RING_ACQ_REL 223
 #define KVM_CAP_S390_PROTECTED_ASYNC_DISABLE 224
 #define KVM_CAP_MEMORY_ATTRIBUTES 225
+#define KVM_CAP_UNMAPPED_PRIVATE_MEM 240
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
-- 
2.25.1