From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6C20C23645F; Thu, 17 Apr 2025 11:12:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744888345; cv=none; b=S9227j0ssDDFMosFj1z5u3/q2oW9pB/sY8vL4Xsl7GinHmaJt00rrWM4WFCifZjoLgC3A6Lr1uGERavvtv/7vnJigoPhTtozjifZiuSJT1ZhtwbRIZ+DI47ZPZ/m4QJh097o9iHc8zNSCewucGItmiE3EC73j8FSXmhCvCLWDz4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744888345; c=relaxed/simple; bh=zKR49UWsXQlKIMA1VnL+BkqgO+3iF8iLPVDDfF2KoTE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qJv86Il9HqLtscLyVepF/2S8m/x0VJulXPSa8zvBWZuchr/O4G6UWUyWFznvNE8KjgnwSqRoajoPJpzF2/wy4MpHHYFytP+KKoPa/sfquDczEHSfMFI+RNlieWHMDIr/7cCW3iixL2DS6JcI2oLoGR6XHX/tZxPEdTqhAfK/izs= ARC-Authentication-Results:i=1; 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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ZIADA/NBWFdjMUgJTKpv9M9Wy2YG9IZEPFByL8wYabsxbBoRuZfKRlm/KXHCD1Dct p+vwf14YsIuc+VHp9bDfack/1J0ZEDi3/LMHCo05xDW9TD4JrJ0GM5fVVA/piqxPhD UyV8JWSU0hR2PMwkuYuHLcqgii53bDcW9KmA0ITTnJZG4RxQYf1Gr8LMHk+DKpR9xo v/L3GNQ4ChUSYncpwgOQsPYYlB/v/0qZd/JiW4t/kLzx/6ZLdqruZ97wB6zyl1mziC tKwEE+12hM3fNBR36tO17t9Oq8pShTsP2t1ihwsRhIESP8RHTn9IcCLiPfhw0jeR7+ 9wRv9KyfJmA3A== Message-ID: Date: Thu, 17 Apr 2025 04:10:59 -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 v1 13/15] x86/msr: Use the alternatives mechanism to read MSR To: Francesco Lavra Cc: acme@kernel.org, adrian.hunter@intel.com, ajay.kaher@broadcom.com, alexander.shishkin@linux.intel.com, andrew.cooper3@citrix.com, bcm-kernel-feedback-list@broadcom.com, boris.ostrovsky@oracle.com, bp@alien8.de, bpf@vger.kernel.org, dave.hansen@linux.intel.com, decui@microsoft.com, haiyangz@microsoft.com, hpa@zytor.com, irogers@google.com, jgross@suse.com, jolsa@kernel.org, kan.liang@linux.intel.com, kvm@vger.kernel.org, kys@microsoft.com, linux-edac@vger.kernel.org, linux-hyperv@vger.kernel.org, linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-pm@vger.kernel.org, llvm@lists.linux.dev, luto@kernel.org, mark.rutland@arm.com, mingo@redhat.com, namhyung@kernel.org, pbonzini@redhat.com, peterz@infradead.org, seanjc@google.com, tglx@linutronix.de, tony.luck@intel.com, virtualization@lists.linux.dev, vkuznets@redhat.com, wei.liu@kernel.org, x86@kernel.org, xen-devel@lists.xenproject.org References: <0f4f2ed70829fffb2eb816e34e26be22681705a5.camel@gmail.com> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; keydata= xsDNBGUPz1cBDACS/9yOJGojBFPxFt0OfTWuMl0uSgpwk37uRrFPTTLw4BaxhlFL0bjs6q+0 2OfG34R+a0ZCuj5c9vggUMoOLdDyA7yPVAJU0OX6lqpg6z/kyQg3t4jvajG6aCgwSDx5Kzg5 Rj3AXl8k2wb0jdqRB4RvaOPFiHNGgXCs5Pkux/qr0laeFIpzMKMootGa4kfURgPhRzUaM1vy bsMsL8vpJtGUmitrSqe5dVNBH00whLtPFM7IbzKURPUOkRRiusFAsw0a1ztCgoFczq6VfAVu raTye0L/VXwZd+aGi401V2tLsAHxxckRi9p3mc0jExPc60joK+aZPy6amwSCy5kAJ/AboYtY VmKIGKx1yx8POy6m+1lZ8C0q9b8eJ8kWPAR78PgT37FQWKYS1uAroG2wLdK7FiIEpPhCD+zH wlslo2ETbdKjrLIPNehQCOWrT32k8vFNEMLP5G/mmjfNj5sEf3IOKgMTMVl9AFjsINLHcxEQ 6T8nGbX/n3msP6A36FDfdSEAEQEAAc0WWGluIExpIDx4aW5Aenl0b3IuY29tPsLBDQQTAQgA NxYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89XBQkFo5qAAhsDBAsJCAcFFQgJCgsFFgID AQAACgkQa70OVx2uN1HUpgv/cM2fsFCQodLArMTX5nt9yqAWgA5t1srri6EgS8W3F+3Kitge tYTBKu6j5BXuXaX3vyfCm+zajDJN77JHuYnpcKKr13VcZi1Swv6Jx1u0II8DOmoDYLb1Q2ZW v83W55fOWJ2g72x/UjVJBQ0sVjAngazU3ckc0TeNQlkcpSVGa/qBIHLfZraWtdrNAQT4A1fa sWGuJrChBFhtKbYXbUCu9AoYmmbQnsx2EWoJy3h7OjtfFapJbPZql+no5AJ3Mk9eE5oWyLH+ QWqtOeJM7kKvn/dBudokFSNhDUw06e7EoVPSJyUIMbYtUO7g2+Atu44G/EPP0yV0J4lRO6EA wYRXff7+I1jIWEHpj5EFVYO6SmBg7zF2illHEW31JAPtdDLDHYcZDfS41caEKOQIPsdzQkaQ oW2hchcjcMPAfyhhRzUpVHLPxLCetP8vrVhTvnaZUo0xaVYb3+wjP+D5j/3+hwblu2agPsaE vgVbZ8Fx3TUxUPCAdr/p73DGg57oHjgezsDNBGUPz1gBDAD4Mg7hMFRQqlzotcNSxatlAQNL MadLfUTFz8wUUa21LPLrHBkUwm8RujehJrzcVbPYwPXIO0uyL/F///CogMNx7Iwo6by43KOy g89wVFhyy237EY76j1lVfLzcMYmjBoTH95fJC/lVb5Whxil6KjSN/R/y3jfG1dPXfwAuZ/4N cMoOslWkfZKJeEut5aZTRepKKF54T5r49H9F7OFLyxrC/uI9UDttWqMxcWyCkHh0v1Di8176 jjYRNTrGEfYfGxSp+3jYL3PoNceIMkqM9haXjjGl0W1B4BidK1LVYBNov0rTEzyr0a1riUrp Qk+6z/LHxCM9lFFXnqH7KWeToTOPQebD2B/Ah5CZlft41i8L6LOF/LCuDBuYlu/fI2nuCc8d m4wwtkou1Y/kIwbEsE/6RQwRXUZhzO6llfoN96Fczr/RwvPIK5SVMixqWq4QGFAyK0m/1ap4 bhIRrdCLVQcgU4glo17vqfEaRcTW5SgX+pGs4KIPPBE5J/ABD6pBnUUAEQEAAcLA/AQYAQgA JhYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89ZBQkFo5qAAhsMAAoJEGu9DlcdrjdR4C0L /RcjolEjoZW8VsyxWtXazQPnaRvzZ4vhmGOsCPr2BPtMlSwDzTlri8BBG1/3t/DNK4JLuwEj OAIE3fkkm+UG4Kjud6aNeraDI52DRVCSx6xff3bjmJsJJMb12mWglN6LjdF6K+PE+OTJUh2F dOhslN5C2kgl0dvUuevwMgQF3IljLmi/6APKYJHjkJpu1E6luZec/lRbetHuNFtbh3xgFIJx 2RpgVDP4xB3f8r0I+y6ua+p7fgOjDLyoFjubRGed0Be45JJQEn7A3CSb6Xu7NYobnxfkwAGZ Q81a2XtvNS7Aj6NWVoOQB5KbM4yosO5+Me1V1SkX2jlnn26JPEvbV3KRFcwV5RnDxm4OQTSk PYbAkjBbm+tuJ/Sm+5Yp5T/BnKz21FoCS8uvTiziHj2H7Cuekn6F8EYhegONm+RVg3vikOpn gao85i4HwQTK9/D1wgJIQkdwWXVMZ6q/OALaBp82vQ2U9sjTyFXgDjglgh00VRAHP7u1Rcu4 l75w1xInsg== In-Reply-To: <0f4f2ed70829fffb2eb816e34e26be22681705a5.camel@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 4/14/2025 10:13 AM, Francesco Lavra wrote: > This works only if this function has been called directly (e.g. via > `call asm_xen_write_msr`), but doesn't work with alternative call types > (like indirect calls). Not sure why one might want to use an indirect > call to invoke asm_xen_write_msr, but this creates a hidden coupling > between caller and callee. > I don't have a suggestion on how to get rid of this coupling, other > than setting ipdelta in _ASM_EXTABLE_FUNC_REWIND() to 0 and adjusting > the _ASM_EXTABLE_TYPE entries at the call sites to consider the > instruction that follows the function call (instead of the call > instruction) as the faulting instruction (which seems pretty ugly, at > least because what follows the function call could be an instruction > that might itself fault). But you may want to make this caveat explicit > in the comment. Good idea, will state that in the comment.