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

[Tom Lendacky]

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&data=04%7C01%7Cthomas.lendacky%40amd.com%7Ca130e2c4b40442b8532108d8b321a57b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637456304409010405%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=6vWmBbFFP0aOaZr31I7WDhpmzL4A%2FY%2BuzvvZrmDHpWI%3D&reserved=0 
> >
> >
> > > +
> > >       pop %_ASM_BX
> > >   #ifdef CONFIG_X86_64
> > > --
> > > 2.25.1