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([2001:b07:6468:f312:4502:3ee3:2bae:c612]) by smtp.gmail.com with ESMTPSA id j5sm18316627wma.45.2020.07.27.05.01.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Jul 2020 05:01:54 -0700 (PDT) Subject: Re: [PATCH 2/2] i386/cpu: Don't add unavailable_features to env->user_features To: Eduardo Habkost , Xiaoyao Li References: <20200713174436.41070-1-xiaoyao.li@intel.com> <20200713174436.41070-3-xiaoyao.li@intel.com> <20200713184841.GF780932@habkost.net> From: Paolo Bonzini Message-ID: <99c4c60f-1d4f-6157-0390-a07f0504be24@redhat.com> Date: Mon, 27 Jul 2020 14:01:53 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200713184841.GF780932@habkost.net> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.81; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/27 03:37:14 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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=-0.01, RCVD_IN_MSPIKE_WL=-0.01, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 13/07/20 20:48, Eduardo Habkost wrote: > On Tue, Jul 14, 2020 at 01:44:36AM +0800, Xiaoyao Li wrote: >> Features unavailable due to absent of their dependent features should >> not be added to env->user_features. env->user_features only contains the >> feature explicity specified with -feature/+feature by user. >> >> Fixes: 99e24dbdaa68 ("target/i386: introduce generic feature dependency mechanism") >> Signed-off-by: Xiaoyao Li > > Paolo, do you remember why that line existed? It doesn't make > sense to me. > > There are exactly 2 lines of code reading user_features, and both > of them are inside x86_cpu_expand_features() above this hunk. I think it was just to be safe in case in the future something else adds features automatically, in the same way as the cpu->max_features case: env->features[w] |= x86_cpu_get_supported_feature_word(w, cpu->migratable) & ~env->user_features[w] & ~feature_word_info[w].no_autoenable_flags; It would prevent the unavailable dependent features from being added. But yeah, it would just be enough to place it above this hunk. Paolo > Reviewed-by: Eduardo Habkost > >> --- >> target/i386/cpu.c | 1 - >> 1 file changed, 1 deletion(-) >> >> diff --git a/target/i386/cpu.c b/target/i386/cpu.c >> index 9812d5747f35..fb1de1bd6165 100644 >> --- a/target/i386/cpu.c >> +++ b/target/i386/cpu.c >> @@ -6370,7 +6370,6 @@ static void x86_cpu_expand_features(X86CPU *cpu, Error **errp) >> unavailable_features & env->user_features[d->to.index], >> "This feature depends on other features that were not requested"); >> >> - env->user_features[d->to.index] |= unavailable_features; >> env->features[d->to.index] &= ~unavailable_features; >> } >> } >> -- >> 2.18.4 >> >