linux-kernel - Re: [PATCH v10 48/50] KVM: SEV: Provide support for SNP_GUEST

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Message-ID: <ZTFD8y5T9nPOpCyX@google.com>
Date:   Thu, 19 Oct 2023 07:57:55 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Alexey Kardashevskiy <aik@....com>
Cc:     Dionna Amalie Glaze <dionnaglaze@...gle.com>,
        Michael Roth <michael.roth@....com>, 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, vkuznets@...hat.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, bp@...en8.de,
        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,
        jarkko@...nel.org, ashish.kalra@....com, nikunj.dadhania@....com,
        pankaj.gupta@....com, liam.merwick@...cle.com,
        zhi.a.wang@...el.com, Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v10 48/50] KVM: SEV: Provide support for SNP_GUEST_REQUEST
 NAE event

On Thu, Oct 19, 2023, Alexey Kardashevskiy wrote:
> 
> On 19/10/23 00:48, Sean Christopherson wrote:
> > static int snp_handle_ext_guest_request(struct vcpu_svm *svm)
> > {
> > 	struct kvm_vcpu *vcpu = &svm->vcpu;
> > 	struct kvm *kvm = vcpu->kvm;
> > 	struct kvm_sev_info *sev;
> > 	unsigned long exitcode;
> > 	u64 data_gpa;
> > 
> > 	if (!sev_snp_guest(vcpu->kvm)) {
> > 		ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SEV_RET_INVALID_GUEST);
> > 		return 1;
> > 	}
> > 
> > 	data_gpa = vcpu->arch.regs[VCPU_REGS_RAX];
> > 	if (!IS_ALIGNED(data_gpa, PAGE_SIZE)) {
> > 		ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SEV_RET_INVALID_ADDRESS);
> > 		return 1;
> > 	}
> > 
> > 	vcpu->run->hypercall.nr		 = KVM_HC_SNP_GET_CERTS;
> > 	vcpu->run->hypercall.args[0]	 = data_gpa;
> > 	vcpu->run->hypercall.args[1]	 = vcpu->arch.regs[VCPU_REGS_RBX];
> > 	vcpu->run->hypercall.flags	 = KVM_EXIT_HYPERCALL_LONG_MODE;
> 
> btw why is it _LONG_MODE and not just _64? :)

I'm pretty sure it got copied from Xen when KVM started adding supporting for
emulating Xen's hypercalls.  I assume Xen PV actually has a need for identifying
long mode as opposed to just 64-bit mode, but KVM, not so much.

> > 	vcpu->arch.complete_userspace_io = snp_complete_ext_guest_request;
> > 	return 0;
> > }
> 
> This should work the KVM stored certs nicely but not for the global certs.
> Although I am not all convinced that global certs is all that valuable but I
> do not know the history of that, happened before I joined so I let others to
> comment on that. Thanks,

Aren't the global certs provided by userspace too though?  If all certs are
ultimately controlled by userspace, I don't see any reason to make the kernel a
middle-man.