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Date: Fri, 20 Jan 2023 21:20:30 +0000
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Michael Roth <michael.roth@....com>
Cc: Borislav Petkov <bp@...en8.de>, kvm@...r.kernel.org,
linux-coco@...ts.linux.dev, linux-mm@...ck.org,
linux-crypto@...r.kernel.org, x86@...nel.org,
linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
luto@...nel.org, dave.hansen@...ux.intel.com, slp@...hat.com,
pgonda@...gle.com, peterz@...radead.org,
srinivas.pandruvada@...ux.intel.com, rientjes@...gle.com,
dovmurik@...ux.ibm.com, tobin@....com, vbabka@...e.cz,
kirill@...temov.name, ak@...ux.intel.com, tony.luck@...el.com,
marcorr@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
alpergun@...gle.com, dgilbert@...hat.com, ashish.kalra@....com,
harald@...fian.com, Nikunj A Dadhania <nikunj@....com>,
chao.p.peng@...ux.intel.com
Subject: Re: [PATCH RFC v7 03/64] KVM: SVM: Advertise private memory support
to KVM
On Wed, Jan 04, 2023 at 08:14:19PM -0600, Michael Roth wrote:
> On Fri, Dec 23, 2022 at 05:56:50PM +0100, Borislav Petkov wrote:
> > On Wed, Dec 14, 2022 at 01:39:55PM -0600, Michael Roth wrote:
> > > + bool (*private_mem_enabled)(struct kvm *kvm);
> >
> > This looks like a function returning boolean to me. IOW, you can
> > simplify this to:
>
> The semantics and existing uses of KVM_X86_OP_OPTIONAL_RET0() gave me the
> impression it needed to return an integer value, since by default if a
> platform doesn't implement the op it would "return 0", and so could
> still be called unconditionally.
>
> Maybe that's not actually enforced, by it seems awkward to try to use a
> bool return instead. At least for KVM_X86_OP_OPTIONAL_RET0().
>
> However, we could just use KVM_X86_OP() to declare it so we can cleanly
> use a function that returns bool, and then we just need to do:
>
> bool kvm_arch_has_private_mem(struct kvm *kvm)
> {
> if (kvm_x86_ops.private_mem_enabled)
> return static_call(kvm_x86_private_mem_enabled)(kvm);
I guess this is missing:
return false;
> }
>
> instead of relying on default return value. So I'll take that approach
> and adopt your other suggested changes.
>
> ...
>
> On a separate topic though, at a high level, this hook is basically a way
> for platform-specific code to tell generic KVM code that private memslots
> are supported by overriding the kvm_arch_has_private_mem() weak
> reference. In this case the AMD platform is using using kvm->arch.upm_mode
> flag to convey that, which is in turn set by the
> KVM_CAP_UNMAPPED_PRIVATE_MEMORY introduced in this series.
>
> But if, as I suggested in response to your PATCH 2 comments, we drop
> KVM_CAP_UNAMMPED_PRIVATE_MEMORY in favor of
> KVM_SET_SUPPORTED_MEMORY_ATTRIBUTES ioctl to enable "UPM mode" in SEV/SNP
> code, then we need to rethink things a bit, since KVM_SET_MEMORY_ATTRIBUTES
> in-part relies on kvm_arch_has_private_mem() to determine what flags are
> supported, whereas SEV/SNP code would be using what was set by
> KVM_SET_MEMORY_ATTRIBUTES to determine the return value in
> kvm_arch_has_private_mem().
Does this mean that internal calls to kvm_vm_set_region_attr() will
cease to exist, and it will rely for user space to use the ioctl
properly instead?
> So, for AMD, the return value of kvm_arch_has_private_mem() needs to rely
> on something else. Maybe the logic can just be:
>
> bool svm_private_mem_enabled(struct kvm *kvm)
> {
> return sev_enabled(kvm) || sev_snp_enabled(kvm)
> }
>
> (at least in the context of this patchset where UPM support is added for
> both SEV and SNP).
>
> So I'll plan to make that change as well.
>
> -Mike
>
> >
> > diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> > index 82ba4a564e58..4449aeff0dff 100644
> > --- a/arch/x86/include/asm/kvm-x86-ops.h
> > +++ b/arch/x86/include/asm/kvm-x86-ops.h
> > @@ -129,6 +129,7 @@ KVM_X86_OP(msr_filter_changed)
> > KVM_X86_OP(complete_emulated_msr)
> > KVM_X86_OP(vcpu_deliver_sipi_vector)
> > KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons);
> > +KVM_X86_OP_OPTIONAL_RET0(private_mem_enabled);
> >
> > #undef KVM_X86_OP
> > #undef KVM_X86_OP_OPTIONAL
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 1da0474edb2d..1b4b89ddeb55 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1574,6 +1574,7 @@ struct kvm_x86_ops {
> >
> > void (*load_mmu_pgd)(struct kvm_vcpu *vcpu, hpa_t root_hpa,
> > int root_level);
> > + bool (*private_mem_enabled)(struct kvm *kvm);
> >
> > bool (*has_wbinvd_exit)(void);
> >
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> > index ce362e88a567..73b780fa4653 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -4680,6 +4680,14 @@ static int svm_vm_init(struct kvm *kvm)
> > return 0;
> > }
> >
> > +static bool svm_private_mem_enabled(struct kvm *kvm)
> > +{
> > + if (sev_guest(kvm))
> > + return kvm->arch.upm_mode;
> > +
> > + return IS_ENABLED(CONFIG_HAVE_KVM_PRIVATE_MEM_TESTING);
> > +}
> > +
> > static struct kvm_x86_ops svm_x86_ops __initdata = {
> > .name = "kvm_amd",
> >
> > @@ -4760,6 +4768,8 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
> >
> > .vcpu_after_set_cpuid = svm_vcpu_after_set_cpuid,
> >
> > + .private_mem_enabled = svm_private_mem_enabled,
> > +
> > .has_wbinvd_exit = svm_has_wbinvd_exit,
> >
> > .get_l2_tsc_offset = svm_get_l2_tsc_offset,
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 823646d601db..9a1ca59d36a4 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -12556,6 +12556,11 @@ void __user * __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
> > }
> > EXPORT_SYMBOL_GPL(__x86_set_memory_region);
> >
> > +bool kvm_arch_has_private_mem(struct kvm *kvm)
> > +{
> > + return static_call(kvm_x86_private_mem_enabled)(kvm);
> > +}
> > +
> > void kvm_arch_pre_destroy_vm(struct kvm *kvm)
> > {
> > kvm_mmu_pre_destroy_vm(kvm);
> >
> > --
> > Regards/Gruss,
> > Boris.
> >
> > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpeople.kernel.org%2Ftglx%2Fnotes-about-netiquette&data=05%7C01%7Cmichael.roth%40amd.com%7C319e89ce555a46eace4d08dae506b51a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638074114318137471%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=aG11K7va1BhemwlKCKKdcIXEwXGUzImYL%2BZ9%2FQ7XToI%3D&reserved=0
BR, Jarkko
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