kvm: nVMX: don't flush VMCS12 during VMXOFF or VCPU teardown (8ca44e88) · Commits · 戴 / test

According to the Intel SDM, software cannot rely on the current VMCS to be coherent after a VMXOFF or shutdown. So this is a valid way to handle VMCS12 flushes. 24.11.1 Software Use of Virtual-Machine Control Structures ... If a logical processor leaves VMX operation, any VMCSs active on that logical processor may be corrupted (see below). To prevent such corruption of a VMCS that may be used either after a return to VMX operation or on another logical processor, software should execute VMCLEAR for that VMCS before executing the VMXOFF instruction or removing power from the processor (e.g., as part of a transition to the S3 and S4 power states). ... This fixes a "suspicious rcu_dereference_check() usage!" warning during kvm_vm_release() because nested_release_vmcs12() calls kvm_vcpu_write_guest_page() without holding kvm->srcu. Signed-off-by:

David Matlack <dmatlack@google.com> Reviewed-by:

Paolo Bonzini <pbonzini@redhat.com> Signed-off-by:

Radim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/vmx.c

+11 −5

Original line number	Diff line number	Diff line
		@@ -419,7 +419,7 @@ struct nested_vmx {
		/*
		* Cache of the guest's VMCS, existing outside of guest memory.
		* Loaded from guest memory during VMPTRLD. Flushed to guest
		* memory during VMXOFF, VMCLEAR, VMPTRLD.
		* memory during VMCLEAR and VMPTRLD.
		*/
		struct vmcs12 *cached_vmcs12;
		/*
		@@ -7174,6 +7174,12 @@ static int nested_vmx_check_permission(struct kvm_vcpu *vcpu)
		return 1;
		}

		static void vmx_disable_shadow_vmcs(struct vcpu_vmx *vmx)
		{
		vmcs_clear_bits(SECONDARY_VM_EXEC_CONTROL, SECONDARY_EXEC_SHADOW_VMCS);
		vmcs_write64(VMCS_LINK_POINTER, -1ull);
		}

		static inline void nested_release_vmcs12(struct vcpu_vmx *vmx)
		{
		if (vmx->nested.current_vmptr == -1ull)
		@@ -7184,9 +7190,7 @@ static inline void nested_release_vmcs12(struct vcpu_vmx *vmx)
		they were modified */
		copy_shadow_to_vmcs12(vmx);
		vmx->nested.sync_shadow_vmcs = false;
		vmcs_clear_bits(SECONDARY_VM_EXEC_CONTROL,
		SECONDARY_EXEC_SHADOW_VMCS);
		vmcs_write64(VMCS_LINK_POINTER, -1ull);
		vmx_disable_shadow_vmcs(vmx);
		}
		vmx->nested.posted_intr_nv = -1;

		@@ -7209,12 +7213,14 @@ static void free_nested(struct vcpu_vmx *vmx)

		vmx->nested.vmxon = false;
		free_vpid(vmx->nested.vpid02);
		nested_release_vmcs12(vmx);
		vmx->nested.posted_intr_nv = -1;
		vmx->nested.current_vmptr = -1ull;
		if (vmx->nested.msr_bitmap) {
		free_page((unsigned long)vmx->nested.msr_bitmap);
		vmx->nested.msr_bitmap = NULL;
		}
		if (enable_shadow_vmcs) {
		vmx_disable_shadow_vmcs(vmx);
		vmcs_clear(vmx->vmcs01.shadow_vmcs);
		free_vmcs(vmx->vmcs01.shadow_vmcs);
		vmx->vmcs01.shadow_vmcs = NULL;

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