On Wed, Mar 4, 2015 at 11:58 PM, Bandan Das <bsd@xxxxxxxxxx> wrote:
> Hi Wincy,
>
> Wincy Van <fanwenyi0529@xxxxxxxxx> writes:
>
>> In commit 3af18d9c5fe9 ("KVM: nVMX: Prepare for using hardware MSR bitmap"),
>> we are setting MSR_BITMAP in prepare_vmcs02 if we should use hardware. This
>> is not enough since the field will be modified by following vmx_set_efer.
>>
>> Fix this by setting vmx_msr_bitmap_nested in vmx_set_msr_bitmap if vcpu is
>> in guest mode.
>>
>> Signed-off-by: Wincy Van <fanwenyi0529@xxxxxxxxx>
>> ---
>> arch/x86/kvm/vmx.c | 11 +++++++----
>> 1 files changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index f7b20b4..10a481b 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -2168,7 +2168,10 @@ static void vmx_set_msr_bitmap(struct kvm_vcpu *vcpu)
>> {
>> unsigned long *msr_bitmap;
>>
>> - if (irqchip_in_kernel(vcpu->kvm) && apic_x2apic_mode(vcpu->arch.apic)) {
>> + if (is_guest_mode(vcpu))
>> + msr_bitmap = vmx_msr_bitmap_nested;
> Do you think this should be (is_guest_mode(vcpu) &
> (exec_control & CPU_BASED_USE_MSR_BITMAPS)) ?
>
We don't need to do that, because if we don't use the hardware, we will disable
hardware msr bitmap:
if (cpu_has_vmx_msr_bitmap() &&
exec_control & CPU_BASED_USE_MSR_BITMAPS) {
nested_vmx_merge_msr_bitmap(vcpu, vmcs12);
/* MSR_BITMAP will be set by following vmx_set_efer. */
} else
exec_control &= ~CPU_BASED_USE_MSR_BITMAPS;
Then, the hardware will ignore MSR_BITMAP.
Setting MSR_BITMAP without enabling it may be unnecessary, but it is no
harm, and we can reduce the code complexity of vmx_set_msr_bitmap.
Thanks,
Wincy
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