linux-kernel - Re: [PATCH 2/4] KVM: SVM: use NPT page attributes

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Message-ID: <559DDCD0.2090502@linux.intel.com>
Date:	Thu, 09 Jul 2015 10:30:40 +0800
From:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
To:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
CC:	jroedel@...e.de, alex.williamson@...hat.com, ogerlitz@...lanox.com,
	amirv@...lanox.com
Subject: Re: [PATCH 2/4] KVM: SVM: use NPT page attributes



On 07/08/2015 07:19 PM, Paolo Bonzini wrote:
>
>
> On 08/07/2015 07:59, Xiao Guangrong wrote:
>>
>>
>> On 07/07/2015 09:45 PM, Paolo Bonzini wrote:
>>> Right now, NPT page attributes are not used, and the final page
>>> attribute depends solely on gPAT (which however is not synced
>>> correctly), the guest MTRRs and the guest page attributes.
>>>
>>> However, we can do better by mimicking what is done for VMX.
>>> In the absence of PCI passthrough, the guest PAT can be ignored
>>> and the page attributes can be just WB.  If passthrough is being
>>> used, instead, keep respecting the guest PAT, and emulate the guest
>>> MTRRs through the PAT field of the nested page tables.
>>>
>>> The only snag is that WP memory cannot be emulated correctly,
>>> because Linux's default PAT setting only includes the other types.
>>>
>>> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
>>> ---
>>>    arch/x86/kvm/svm.c | 47 ++++++++++++++++++++++++++++++++++++++++++-----
>>>    1 file changed, 42 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>>> index 602b974a60a6..0f125c1860ec 100644
>>> --- a/arch/x86/kvm/svm.c
>>> +++ b/arch/x86/kvm/svm.c
>>> @@ -1085,6 +1085,47 @@ static u64 svm_compute_tsc_offset(struct
>>> kvm_vcpu *vcpu, u64 target_tsc)
>>>        return target_tsc - tsc;
>>>    }
>>>
>>> +static void svm_set_guest_pat(struct vcpu_svm *svm, u64 *g_pat)
>>> +{
>>> +    struct kvm_vcpu *vcpu = &svm->vcpu;
>>> +
>>> +    /* Unlike Intel, AMD takes the guest's CR0.CD into account.
>>
>> I noticed this code in svm_set_cr0():
>>
>>      if (!(vcpu->kvm->arch.disabled_quirks & KVM_QUIRK_CD_NW_CLEARED))
>>          cr0 &= ~(X86_CR0_CD | X86_CR0_NW);
>>
>> gCR0.CD is hidden to CPU if KVM_QUIRK_CD_NW_CLEARED is not set and looks
>> like
>> it is the normal case after grepping Qemu code.
>>

How about this one? I still do not know how SVM properly emulates CR0.CD? :(
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