[PATCH v2] KVM: vmx: Set msr bitmap correctly if vcpu is in guest mode

[PATCH v2] KVM: vmx: Set msr bitmap correctly if vcpu is in guest mode

[Wincy Van]

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@gmail.com>
---
 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;
+	else if (irqchip_in_kernel(vcpu->kvm) &&
+		apic_x2apic_mode(vcpu->arch.apic)) {
 		if (is_long_mode(vcpu))
 			msr_bitmap = vmx_msr_bitmap_longmode_x2apic;
 		else
@@ -9218,9 +9221,9 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 	}
 
 	if (cpu_has_vmx_msr_bitmap() &&
-	    exec_control & CPU_BASED_USE_MSR_BITMAPS &&
-	    nested_vmx_merge_msr_bitmap(vcpu, vmcs12)) {
-		vmcs_write64(MSR_BITMAP, __pa(vmx_msr_bitmap_nested));
+	    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;
 
-- 
1.7.1

Re: [PATCH v2] KVM: vmx: Set msr bitmap correctly if vcpu is in guest mode

[Bandan Das]

Hi Wincy,

Wincy Van <fanwenyi0529@gmail.com> 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@gmail.com>
> ---
>  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)) ?

> +	else if (irqchip_in_kernel(vcpu->kvm) &&
> +		apic_x2apic_mode(vcpu->arch.apic)) {
>  		if (is_long_mode(vcpu))
>  			msr_bitmap = vmx_msr_bitmap_longmode_x2apic;
>  		else
> @@ -9218,9 +9221,9 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
>  	}
>  
>  	if (cpu_has_vmx_msr_bitmap() &&
> -	    exec_control & CPU_BASED_USE_MSR_BITMAPS &&
> -	    nested_vmx_merge_msr_bitmap(vcpu, vmcs12)) {
> -		vmcs_write64(MSR_BITMAP, __pa(vmx_msr_bitmap_nested));
> +	    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;

Re: [PATCH v2] KVM: vmx: Set msr bitmap correctly if vcpu is in guest mode

[Wincy Van]

On Wed, Mar 4, 2015 at 11:58 PM, Bandan Das <bsd@redhat.com> wrote:
> Hi Wincy,
>
> Wincy Van <fanwenyi0529@gmail.com> 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@gmail.com>
>> ---
>>  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

Re: [PATCH v2] KVM: vmx: Set msr bitmap correctly if vcpu is in guest mode

[Marcelo Tosatti]

On Wed, Mar 04, 2015 at 02:31:56PM +0800, Wincy Van wrote:
> 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@gmail.com>

Applied, thanks.