linux-kernel - Re: [PATCH 3/3] X86/nVMX: Update the MSR_BITMAP field with the L02 MSR BITMAP

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Message-ID: <8d50836c-4eee-15ef-da20-212559105594@amazon.com>
Date:   Sat, 10 Feb 2018 00:41:54 +0100
From:   KarimAllah Ahmed <karahmed@...zon.com>
To:     Jim Mattson <jmattson@...gle.com>,
        KarimAllah Ahmed <karahmed@...zon.de>
CC:     kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH 3/3] X86/nVMX: Update the MSR_BITMAP field with the L02
 MSR BITMAP

On 02/10/2018 12:26 AM, Jim Mattson wrote:
> On Thu, Feb 8, 2018 at 2:53 PM, KarimAllah Ahmed <karahmed@...zon.de> wrote:
>> ... otherwise we will just be running with the L1 MSR BITMAP!
>>
>> It does not seem that we ever update the MSR_BITMAP when the nested guest
>> is running. The only place where we update the MSR_BITMAP field in VMCS is
>> for the L1 guest!
>>
>> Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: kvm@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org
>> ---
>>   arch/x86/kvm/vmx.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 91e3539..f40be10 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -10589,6 +10589,9 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
>>          vmcs_writel(GUEST_GDTR_BASE, vmcs12->guest_gdtr_base);
>>          vmcs_writel(GUEST_IDTR_BASE, vmcs12->guest_idtr_base);
>>
>> +       if (cpu_has_vmx_msr_bitmap())
>> +               vmcs_write64(MSR_BITMAP, __pa(vmx->nested.vmcs02.msr_bitmap));
>> +
> 
> This is already in David's "[PATCH 5/9] KVM: VMX: make MSR bitmaps
> per-VCPU," isn't it?

I assume you are referring to this:

https://patchwork.kernel.org/patch/10194819/

.. which is now:

commit 904e14fb7cb9 ("KVM: VMX: make MSR bitmaps per-VCPU")

right?

If this is the case, then I do not see where the MSR_BITMAP is being
updated here. In fact, would not this be the commit that actually broke
it?

Now MSR_BITMAP is only set in vmx_vcpu_setup:

         if (cpu_has_vmx_msr_bitmap())
                 vmcs_write64(MSR_BITMAP, __pa(vmx->vmcs01.msr_bitmap));

> 
>>          if (from_vmentry &&
>>              (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS)) {
>>                  kvm_set_dr(vcpu, 7, vmcs12->guest_dr7);
>> --
>> 2.7.4
>>
> 
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