linux-kernel - Re: [PATCH v3 1/3] KVM: SVM: use vmsave/vmload for saving/restoring additional host state

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Date:   Thu, 7 Jan 2021 09:47:52 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Michael Roth <michael.roth@....com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Andy Lutomirski <luto@...capital.net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] KVM: SVM: use vmsave/vmload for saving/restoring
 additional host state



On 1/7/21 9:32 AM, Tom Lendacky wrote:
> On 1/5/21 11:20 AM, Sean Christopherson wrote:
>> On Tue, Jan 05, 2021, Michael Roth wrote:
>>> @@ -3703,16 +3688,9 @@ static noinstr void svm_vcpu_enter_exit(struct 
>>> kvm_vcpu *vcpu,
>>>       if (sev_es_guest(svm->vcpu.kvm)) {
>>>           __svm_sev_es_vcpu_run(svm->vmcb_pa);
>>>       } else {
>>> -        __svm_vcpu_run(svm->vmcb_pa, (unsigned long 
>>> *)&svm->vcpu.arch.regs);
>>> -
>>> -#ifdef CONFIG_X86_64
>>> -        native_wrmsrl(MSR_GS_BASE, svm->host.gs_base);
>>> -#else
>>> -        loadsegment(fs, svm->host.fs);
>>> -#ifndef CONFIG_X86_32_LAZY_GS
>>> -        loadsegment(gs, svm->host.gs);
>>> -#endif
>>> -#endif
>>> +        __svm_vcpu_run(svm->vmcb_pa, (unsigned long 
>>> *)&svm->vcpu.arch.regs,
>>> +                   page_to_phys(per_cpu(svm_data,
>>> +                            vcpu->cpu)->save_area));
>>
>> Does this need to use __sme_page_pa()?
> 
> Yes, it should now. The SEV-ES support added the SME encryption bit to the 
> MSR_VM_HSAVE_PA MSR, so we need to be consistent in how the data is read 
> and written.

Oh, and also in svm_vcpu_load().

Thanks,
Tom

>  > Thanks,
> Tom
> 
>>
>>>       }
>>>       /*
>>
>> ...
>>
>>> diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
>>> index 6feb8c08f45a..89f4e8e7bf0e 100644
>>> --- a/arch/x86/kvm/svm/vmenter.S
>>> +++ b/arch/x86/kvm/svm/vmenter.S
>>> @@ -33,6 +33,7 @@
>>>    * __svm_vcpu_run - Run a vCPU via a transition to SVM guest mode
>>>    * @vmcb_pa:    unsigned long
>>>    * @regs:    unsigned long * (to guest registers)
>>> + * @hostsa_pa:    unsigned long
>>>    */
>>>   SYM_FUNC_START(__svm_vcpu_run)
>>>       push %_ASM_BP
>>> @@ -47,6 +48,9 @@ SYM_FUNC_START(__svm_vcpu_run)
>>>   #endif
>>>       push %_ASM_BX
>>> +    /* Save @hostsa_pa */
>>> +    push %_ASM_ARG3
>>> +
>>>       /* Save @regs. */
>>>       push %_ASM_ARG2
>>> @@ -154,6 +158,12 @@ SYM_FUNC_START(__svm_vcpu_run)
>>>       xor %r15d, %r15d
>>>   #endif
>>> +    /* "POP" @hostsa_pa to RAX. */
>>> +    pop %_ASM_AX
>>> +
>>> +    /* Restore host user state and FS/GS base */
>>> +    vmload %_ASM_AX
>>
>> This VMLOAD needs the "handle fault on reboot" goo.  Seeing the code, I 
>> think
>> I'd prefer to handle this in C code, especially if Paolo takes the 
>> svm_ops.h
>> patch[*].  Actually, I think with that patch it'd make sense to move the
>> existing VMSAVE+VMLOAD for the guest into svm.c, too.  And completely 
>> unrelated,
>> the fault handling in svm/vmenter.S can be cleaned up a smidge to 
>> eliminate the
>> JMPs.
>>
>> Paolo, what do you think about me folding these patches into my series 
>> to do the
>> above cleanups?  And maybe sending a pull request for the end result?  
>> (I'd also
>> like to add on a patch to use the user return MSR mechanism for 
>> MSR_TSC_AUX).
>>
>> [*] 
>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.kernel.org%2Fr%2F20201231002702.2223707-8-seanjc%40google.com&amp;data=04%7C01%7Cthomas.lendacky%40amd.com%7Ca130e2c4b40442b8532108d8b321a57b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637456304409010405%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=6vWmBbFFP0aOaZr31I7WDhpmzL4A%2FY%2BuzvvZrmDHpWI%3D&amp;reserved=0 
>>
>>
>>> +
>>>       pop %_ASM_BX
>>>   #ifdef CONFIG_X86_64
>>> -- 
>>> 2.25.1
>>>