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 09:32:37 -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 1/5/21 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.

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%7C5125acb3a3384ee75a5c08d8b19e2888%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637454640159484993%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=Q%2F%2B7kxE9pcV%2BelzHbeRpvs8wlQGQkirKUPg7fBP3QbU%3D&amp;reserved=0
> 
>> +
>>   	pop %_ASM_BX
>>   
>>   #ifdef CONFIG_X86_64
>> -- 
>> 2.25.1
>>