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[2003:f6:af11:1a00:2774:82c0:51ec:a183]) by smtp.gmail.com with ESMTPSA id c23-20020a170906155700b00869f2ca6a87sm10397579ejd.135.2023.02.01.11.44.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Feb 2023 11:44:26 -0800 (PST) From: Mathias Krause To: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Sean Christopherson , Paolo Bonzini , Mathias Krause Subject: [PATCH v3 2/6] KVM: VMX: Avoid retpoline call for control register caused exits Date: Wed, 1 Feb 2023 20:46:00 +0100 Message-Id: <20230201194604.11135-3-minipli@grsecurity.net> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230201194604.11135-1-minipli@grsecurity.net> References: <20230201194604.11135-1-minipli@grsecurity.net> MIME-Version: 1.0 X-Spam-Status: No, score=-1.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS autolearn=no 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 X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1756659600770136687?= X-GMAIL-MSGID: =?utf-8?q?1756659600770136687?= Complement commit 4289d2728664 ("KVM: retpolines: x86: eliminate retpoline from vmx.c exit handlers") and avoid a retpoline call for control register accesses as well. This speeds up guests that make heavy use of it, like grsecurity kernels toggling CR0.WP to implement kernel W^X. Signed-off-by: Mathias Krause --- Meanwhile I got my hands on a AMD system and while doing a similar change for SVM gives a small measurable win (1.1% faster for grsecurity guests), it would provide nothing for other guests, as the change I was testing was specifically targeting CR0 caused exits. A more general approach would instead cover CR3 and, maybe, CR4 as well. However, that would require a lot more exit code compares, likely vanishing the gains in the general case. So this tweak is VMX only. arch/x86/kvm/vmx/vmx.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index c788aa382611..c8198c8a9b55 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6538,6 +6538,8 @@ static int __vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath) return handle_external_interrupt(vcpu); else if (exit_reason.basic == EXIT_REASON_HLT) return kvm_emulate_halt(vcpu); + else if (exit_reason.basic == EXIT_REASON_CR_ACCESS) + return handle_cr(vcpu); else if (exit_reason.basic == EXIT_REASON_EPT_MISCONFIG) return handle_ept_misconfig(vcpu); #endif