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

[Tom Lendacky]

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&data=04%7C01%7Cthomas.lendacky%40amd.com%7C5125acb3a3384ee75a5c08d8b19e2888%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637454640159484993%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=Q%2F%2B7kxE9pcV%2BelzHbeRpvs8wlQGQkirKUPg7fBP3QbU%3D&reserved=0
>
> > +
> >   	pop %_ASM_BX
> >   
> >   #ifdef CONFIG_X86_64
> > --
> > 2.25.1