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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.149, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 10/9/24 10:12, Chao Gao wrote: >>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c >>> index 85ef7452c0..18ba958f46 100644 >>> --- a/target/i386/cpu.c >>> +++ b/target/i386/cpu.c >>> @@ -1148,8 +1148,8 @@ FeatureWordInfo feature_word_info[FEATURE_WORDS] = { >>> [FEAT_7_2_EDX] = { >>> .type = CPUID_FEATURE_WORD, >>> .feat_names = { >>> - NULL, NULL, NULL, NULL, >>> - NULL, "mcdt-no", NULL, NULL, >>> + "intel-psfd", "ipred-ctrl", "rrsba-ctrl", "ddpd-u", >>> + "bhi-ctrl", "mcdt-no", NULL, NULL, >> >> IIUC, these bits depend on "spec-ctrl", which indicates the presence of >> IA32_SPEC_CTRL. >> >> Then I think we'd better add dependencies in feature_dependencies[]. > > (+ kvm mailing list) > > Thanks for pointing that out. It seems that any of these bits imply the > presence of IA32_SPEC_CTRL. According to SDM vol4, chapter 2, table 2.2, > the 'Comment' column for the IA32_SPEC_CTRL MSR states: > > If any one of the enumeration conditions for defined bit field positions holds. > > So, it might be more appropriate to fix KVM's handling of the > IA32_SPEC_CTRL MSR (i.e., guest_has_spec_ctrl_msr()). > > what do you think? You're right, the spec-ctrl CPUID feature covers the IBRS bit of MSR_IA32_SPEC_CTRL and also the IBPB feature of MSR_IA32_PRED_CMD. It does not specify the existence of MSR_IA32_SPEC_CTRL. In practice it's probably not a good idea to omit spec-ctrl when passing other features to the guest that cover that MSR; but the specification says it's fine. Paolo