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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: Nadav Har'El <nyh@il.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Nadav Har'El 2011-08-02 15:54:52 +03:00 committed by Avi Kivity
parent d5c1785d2f
commit 27fc51b21c
1 changed files with 21 additions and 10 deletions
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31
arch/x86/kvm/vmx.c
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@ -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);
vmcs_write64(TSC_OFFSET,
vmx->nested.vmcs01_tsc_offset + vmcs12->tsc_offset);
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 */