Commit 27fc51b2 authored by Nadav Har'El's avatar Nadav Har'El Committed by Avi Kivity
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KVM: nVMX: Fix nested VMX TSC emulation 



This patch fixes two corner cases in nested (L2) handling of TSC-related
issues:

1. Somewhat suprisingly, according to the Intel spec, if L1 allows WRMSR to
the TSC MSR without an exit, then this should set L1's TSC value itself - not
offset by vmcs12.TSC_OFFSET (like was wrongly done in the previous code).

2. Allow L1 to disable the TSC_OFFSETING control, and then correctly ignore
the vmcs12.TSC_OFFSET.

Signed-off-by: default avatarNadav Har'El <nyh@il.ibm.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent d5c1785d

arch/x86/kvm/vmx.c

+21 −10
Original line number Diff line number Diff line
@@ -1777,15 +1777,23 @@ static void vmx_set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz) 
 */

static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)

{

	vmcs_write64(TSC_OFFSET, offset);

	if (is_guest_mode(vcpu))

	if (is_guest_mode(vcpu)) {

		/*

		 * We're here if L1 chose not to trap the TSC MSR. Since

		 * prepare_vmcs12() does not copy tsc_offset, we need to also

		 * set the vmcs12 field here.

		 * We're here if L1 chose not to trap WRMSR to TSC. According

		 * to the spec, this should set L1's TSC; The offset that L1

		 * set for L2 remains unchanged, and still needs to be added

		 * to the newly set TSC to get L2's TSC.

		 */

		get_vmcs12(vcpu)->tsc_offset = offset -

			to_vmx(vcpu)->nested.vmcs01_tsc_offset;

		struct vmcs12 *vmcs12;

		to_vmx(vcpu)->nested.vmcs01_tsc_offset = offset;

		/* recalculate vmcs02.TSC_OFFSET: */

		vmcs12 = get_vmcs12(vcpu);

		vmcs_write64(TSC_OFFSET, offset +

			(nested_cpu_has(vmcs12, CPU_BASED_USE_TSC_OFFSETING) ?

			 vmcs12->tsc_offset : 0));

	} else {

		vmcs_write64(TSC_OFFSET, offset);

	}

}



static void vmx_adjust_tsc_offset(struct kvm_vcpu *vcpu, s64 adjustment)
@@ -6485,8 +6493,11 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12) 


	set_cr4_guest_host_mask(vmx);



	if (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETING)

		vmcs_write64(TSC_OFFSET,

			vmx->nested.vmcs01_tsc_offset + vmcs12->tsc_offset);

	else

		vmcs_write64(TSC_OFFSET, vmx->nested.vmcs01_tsc_offset);



	if (enable_vpid) {

		/*
@@ -6893,7 +6904,7 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu) 


	load_vmcs12_host_state(vcpu, vmcs12);



	/* Update TSC_OFFSET if vmx_adjust_tsc_offset() was used while L2 ran */

	/* Update TSC_OFFSET if TSC was changed while L2 ran */

	vmcs_write64(TSC_OFFSET, vmx->nested.vmcs01_tsc_offset);



	/* This is needed for same reason as it was needed in prepare_vmcs02 */

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