[PATCH] KVM: improve definition of KVM_GET/SET_NESTED_STATE structs

[Paolo Bonzini]

Liran sent me a patch with a large overhaul of the
KVM_GET/SET_NESTED_STATE structs.  However, I am wary of changing the
userspace ABI in backwards-incompatible ways, so here is the bare minimum
that is needed to achieve the same functionality.

Namely, the format of VMX nested state is detailed in a struct, and is
accessible through struct kvm_vmx_nested_state.  Unfortunately, to avoid
changing the size of the structs it has to be accessed as "vmx.data[0]"
rather than just "vmx.data".

Also, the values of the "format" field are defined as macros, which is
easy and not controversial.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/include/uapi/asm/kvm.h | 11 +++++++++++
 arch/x86/kvm/vmx/nested.c       |  3 +++
 2 files changed, 14 insertions(+)

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 7a0e64ccd6ff..06b8727a3b58 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -383,6 +383,9 @@ struct kvm_sync_regs {
 #define KVM_X86_QUIRK_LAPIC_MMIO_HOLE	(1 << 2)
 #define KVM_X86_QUIRK_OUT_7E_INC_RIP	(1 << 3)
 
+#define KVM_STATE_NESTED_FORMAT_VMX	0
+#define KVM_STATE_NESTED_FORMAT_SVM	1
+
 #define KVM_STATE_NESTED_GUEST_MODE	0x00000001
 #define KVM_STATE_NESTED_RUN_PENDING	0x00000002
 #define KVM_STATE_NESTED_EVMCS		0x00000004
@@ -390,6 +393,11 @@ struct kvm_sync_regs {
 #define KVM_STATE_NESTED_SMM_GUEST_MODE	0x00000001
 #define KVM_STATE_NESTED_SMM_VMXON	0x00000002
 
+struct kvm_vmx_nested_state_data {
+	__u8 vmcs12[0x1000];
+	__u8 shadow_vmcs12[0x1000];
+};
+
 struct kvm_vmx_nested_state {
 	__u64 vmxon_pa;
 	__u64 vmcs_pa;
@@ -397,6 +405,9 @@ struct kvm_vmx_nested_state {
 	struct {
 		__u16 flags;
 	} smm;
+
+	__u8 pad[120 - 18];
+	struct kvm_vmx_nested_state_data data[0];
 };
 
 /* for KVM_CAP_NESTED_STATE */
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 0c601d079cd2..d97b87ef209b 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5269,6 +5269,9 @@ static int vmx_get_nested_state(struct kvm_vcpu *vcpu,
 		.vmx.vmcs_pa = -1ull,
 	};
 
+	BUILD_BUG_ON(sizeof(struct kvm_vmx_nested_state)
+		     != sizeof_field(struct kvm_nested_state, pad));
+
 	if (!vcpu)
 		return kvm_state.size + 2 * VMCS12_SIZE;
 
-- 
2.21.0