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Dadhania" , linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org, mingo@redhat.com, tglx@linutronix.de, dave.hansen@linux.intel.com, seanjc@google.com, pbonzini@redhat.com, thomas.lendacky@amd.com, michael.roth@amd.com, stable@kernel.org Subject: Re: [PATCH v3] x86/sev: Add SEV-SNP guest feature negotiation support In-Reply-To: Message-ID: <05171aad-bcef-a731-970f-726b393e3ad3@google.com> References: <20230102083810.71178-1-nikunj@amd.com> <3169b54b-d990-7707-5ec4-cde7261318fe@google.com> <45487a87-764a-7ff3-292b-4a55fe29f7ba@amd.com> <02a2e641-6b6d-e1c5-2c43-8815306d92a0@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Spam-Status: No, score=-17.6 required=5.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, ENV_AND_HDR_SPF_MATCH,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL,USER_IN_DEF_SPF_WL autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 3 Jan 2023, Borislav Petkov wrote: > On Tue, Jan 03, 2023 at 09:07:14AM +0530, Nikunj A. Dadhania wrote: > > Currently, GHCBData[24:63] is unused. If we intend to use the bit range(40bits), GHCB spec > > will need to be updated. And probably would not be enough. > > My fear too... > > > As the termination request is done using GHCB MSR protocol, exit codes cannot be used. > > We need to figure out some other way of communicating to the guest owner because > of which feature the guest refused booting. > Yeah, this was exactly the thought. If the guest terminates because SNP_FEAT_NOT_IMPLEMENTED, it seems necessary to provide information on which feature(s) the guest is lacking an implementation for that the hypervisor has enabled. Otherwise this becomes a frustrating trial and error for the customer.