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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=aTCKescadr0sHc1OBNab3mt0WNOdORNOUu7rpBETQ6vGwSMvW5FXLhE2vfj1fe1w6 kxqgtHLh80BykH4vNphE7UVD2umMuSaHZ0X7BB8pQmc61E8lzA//9+HuTE4ROZLaHQ dQx1WOTNwbk243SjOLe1tpFcPH9y12xx7ogDIZhREF4ji6RETc9TF7kIMeKjF5mIsX eMDXrP0TRl7JUiIRx2OTEz9i2vbZmrKeMtWUxjkY/XflI7iXlGFVwA24g71d0hbH9Y ZcmCp02WLH6iMipEkRPpY3a67hmjRhqj5K+CZV5FH7x7JFpmsNnSuIPtKmy58Xt4bk MKbcDfnoCUCnA== Message-ID: <7fea6158-9b7d-4bfb-b709-729266803c32@zytor.com> Date: Tue, 22 Apr 2025 02:20:32 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2 22/34] x86/msr: Utilize the alternatives mechanism to read MSR To: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-hyperv@vger.kernel.org, virtualization@lists.linux.dev, linux-pm@vger.kernel.org, linux-edac@vger.kernel.org, xen-devel@lists.xenproject.org, linux-acpi@vger.kernel.org, linux-hwmon@vger.kernel.org, netdev@vger.kernel.org, platform-driver-x86@vger.kernel.org Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, acme@kernel.org, andrew.cooper3@citrix.com, peterz@infradead.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com, wei.liu@kernel.org, ajay.kaher@broadcom.com, bcm-kernel-feedback-list@broadcom.com, tony.luck@intel.com, pbonzini@redhat.com, vkuznets@redhat.com, seanjc@google.com, luto@kernel.org, boris.ostrovsky@oracle.com, kys@microsoft.com, haiyangz@microsoft.com, decui@microsoft.com References: <20250422082216.1954310-1-xin@zytor.com> <20250422082216.1954310-23-xin@zytor.com> <91f9217a-cc2d-4a6e-bada-290312f73d82@suse.com> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 4/22/2025 1:59 AM, Jürgen Groß wrote: > On 22.04.25 10:22, Xin Li (Intel) wrote: >> To eliminate the indirect call overhead introduced by the pv_ops API, >> utilize the alternatives mechanism to read MSR: >> >>      1) When built with !CONFIG_XEN_PV, X86_FEATURE_XENPV becomes a >>         disabled feature, preventing the Xen code from being built >>         and ensuring the native code is executed unconditionally. >> >>      2) When built with CONFIG_XEN_PV: >> >>         2.1) If not running on the Xen hypervisor (!X86_FEATURE_XENPV), >>              the kernel runtime binary is patched to unconditionally >>              jump to the native MSR read code. >> >>         2.2) If running on the Xen hypervisor (X86_FEATURE_XENPV), the >>              kernel runtime binary is patched to unconditionally jump >>              to the Xen MSR read code. >> >> The alternatives mechanism is also used to choose the new immediate >> form MSR read instruction when it's available. >> >> Consequently, remove the pv_ops MSR read APIs and the Xen callbacks. > > Same as the comment to patch 5: there is no indirect call overhead after > the system has come up. > Please check https://lore.kernel.org/lkml/87y1h81ht4.ffs@tglx/. And it's was also mentioned in the previous patch: https://lore.kernel.org/lkml/20250422082216.1954310-22-xin@zytor.com/ Please let me know what I have missed. Thanks! Xin