linux-kernel - Re: [PATCH Part2 RFC v2 36/37] KVM: SVM: Provide support for SNP_GUEST

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Date:   Mon, 10 May 2021 12:57:27 -0600
From:   Peter Gonda <pgonda@...gle.com>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        kvm list <kvm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, jroedel@...e.de,
        "Lendacky, Thomas" <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>, peterz@...radead.org,
        "H. Peter Anvin" <hpa@...or.com>, tony.luck@...el.com
Subject: Re: [PATCH Part2 RFC v2 36/37] KVM: SVM: Provide support for
 SNP_GUEST_REQUEST NAE event

>
> +static void snp_handle_guest_request(struct vcpu_svm *svm, struct ghcb *ghcb,
> +                                   gpa_t req_gpa, gpa_t resp_gpa)
> +{
> +       struct sev_data_snp_guest_request data = {};
> +       struct kvm_vcpu *vcpu = &svm->vcpu;
> +       struct kvm *kvm = vcpu->kvm;
> +       kvm_pfn_t req_pfn, resp_pfn;
> +       struct kvm_sev_info *sev;
> +       int rc, err = 0;
> +
> +       if (!sev_snp_guest(vcpu->kvm)) {
> +               rc = -ENODEV;
> +               goto e_fail;
> +       }
> +
> +       sev = &to_kvm_svm(kvm)->sev_info;
> +
> +       if (!__ratelimit(&sev->snp_guest_msg_rs)) {
> +               pr_info_ratelimited("svm: too many guest message requests\n");
> +               rc = -EAGAIN;
> +               goto e_fail;
> +       }
> +
> +       if (!IS_ALIGNED(req_gpa, PAGE_SIZE) || !IS_ALIGNED(resp_gpa, PAGE_SIZE)) {
> +               pr_err("svm: guest request (%#llx) or response (%#llx) is not page aligned\n",
> +                       req_gpa, resp_gpa);
> +               goto e_term;
> +       }
> +
> +       req_pfn = gfn_to_pfn(kvm, gpa_to_gfn(req_gpa));
> +       if (is_error_noslot_pfn(req_pfn)) {
> +               pr_err("svm: guest request invalid gpa=%#llx\n", req_gpa);
> +               goto e_term;
> +       }
> +
> +       resp_pfn = gfn_to_pfn(kvm, gpa_to_gfn(resp_gpa));
> +       if (is_error_noslot_pfn(resp_pfn)) {
> +               pr_err("svm: guest response invalid gpa=%#llx\n", resp_gpa);
> +               goto e_term;
> +       }
> +
> +       data.gctx_paddr = __psp_pa(sev->snp_context);
> +       data.req_paddr = __sme_set(req_pfn << PAGE_SHIFT);
> +       data.res_paddr = __psp_pa(sev->snp_resp_page);
> +
> +       mutex_lock(&kvm->lock);
> +
> +       rc = sev_issue_cmd(kvm, SEV_CMD_SNP_GUEST_REQUEST, &data, &err);
> +       if (rc) {
> +               mutex_unlock(&kvm->lock);
> +
> +               /* If we have a firmware error code then use it. */
> +               if (err)
> +                       rc = err;
> +
> +               goto e_fail;
> +       }
> +
> +       /* Copy the response after the firmware returns success. */
> +       rc = kvm_write_guest(kvm, resp_gpa, sev->snp_resp_page, PAGE_SIZE);
> +
> +       mutex_unlock(&kvm->lock);
> +
> +e_fail:
> +       ghcb_set_sw_exit_info_2(ghcb, rc);
> +       return;
> +
> +e_term:
> +       ghcb_set_sw_exit_info_1(ghcb, 1);
> +       ghcb_set_sw_exit_info_2(ghcb,
> +                               X86_TRAP_GP |
> +                               SVM_EVTINJ_TYPE_EXEPT |
> +                               SVM_EVTINJ_VALID);
> +}

I am probably missing something in the spec but I don't see any
references to #GP in the '4.1.7 SNP Guest Request' section. Why is
this different from e_fail?