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 CDD392701B5; Wed, 23 Apr 2025 09:28:45 +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=1745400528; cv=none; b=pORcwe7OPLEKwzN0vQimRV/3TAax5zfJC+ISP2m6LhbiW35rlaQ3PRBFlUX9wU5IHR5p9khUKWjyj7tgZh9Bp7i0FmGiwsteZJ77R08U6PQfzEQH9qw0oK43e079VSfUmBi2ZuzEZxGLXUm6FPVdHxMjQxEmOeuXi1G8AdQvjD0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745400528; c=relaxed/simple; bh=+EYVuYrtu0aOqe3lbGO7b9PG5zqWh+Kau/58q5Ikx7w=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=SiqJAvCjPomS4sFbbZsaZrXnie+44uUS1W9DkZ8drnHCb3FDPGo7J+hd443HMoXUHPKJVrkH/DAxRQyf0/Ke/WIbRIXKIeUS4clA6JXMrzUTfs8mYfzqNsZ2UOFpaf1SSkbhgYBvGDiYKtX0vb5GkPpFu52sFWHbRS4a4fPxQvU= ARC-Authentication-Results:i=1; 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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=UmIumy9ccUWtp5ZpbFY6Ho9GgYRlVSRySL3D0+L6jUnzCuWo+VAXnfIYm+WcNWHcr 3vdBJ+wwDthlqUfiIoaN3DvHPiYn4gb/+Mbw6citZ1Nn3xuBxFNqKSFdRNvSlmfDHg sgDUE/YJgzJJyaLCEhkxOt4S6E7bN3HrTuYY85xE4DOyVvo6Ap2JfPnfbPyl+GWU88 BCLMSAjhGktSUoCdwdyy/ZS83Z3KwNGZuWXVpY05BNcjcn6RiyoIM0nH70HIaJUZTW sxPrQvxiLK2+ljs3l/mZq4cz6GbUS+eJfVvDu2BEsKu2EVOjGnH6pzErQiG0qnjLGr yA9/DCpyDaO8g== Message-ID: <7527f09c-7163-4276-b9a4-edac6c8217ae@zytor.com> Date: Wed, 23 Apr 2025 02:27:46 -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 10/34] x86/msr: Convert __rdmsr() uses to native_rdmsrq() uses To: Sean Christopherson Cc: 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, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, acme@kernel.org, jgross@suse.com, 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, luto@kernel.org, boris.ostrovsky@oracle.com, kys@microsoft.com, haiyangz@microsoft.com, decui@microsoft.com References: <20250422082216.1954310-1-xin@zytor.com> <20250422082216.1954310-11-xin@zytor.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: 7bit On 4/22/2025 8:09 AM, Sean Christopherson wrote: > On Tue, Apr 22, 2025, Xin Li (Intel) wrote: >> __rdmsr() is the lowest level primitive MSR read API, and its direct >> use is NOT preferred. > > Doesn't mean it's wrong. I wouldn't go so far as to claim that it's wrong :-) >> Use its wrapper function native_rdmsrq() instead. The current code exhibits a somewhat haphazard use of MSR APIs, so I wanted to clarify which API to employ in specific situations with verbose function naming. Here is an example that Boris had to fix the use of MSR APIs: https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f980f9c31a923e9040dee0bc679a5f5b09e61f40 > > ... > >> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c >> index 1547bfacd40f..e73c1d5ba6c4 100644 >> --- a/arch/x86/kvm/vmx/vmx.c >> +++ b/arch/x86/kvm/vmx/vmx.c >> @@ -380,7 +380,7 @@ static __always_inline void vmx_disable_fb_clear(struct vcpu_vmx *vmx) >> if (!vmx->disable_fb_clear) >> return; >> >> - msr = __rdmsr(MSR_IA32_MCU_OPT_CTRL); >> + msr = native_rdmsrq(MSR_IA32_MCU_OPT_CTRL); >> msr |= FB_CLEAR_DIS; >> native_wrmsrq(MSR_IA32_MCU_OPT_CTRL, msr); >> /* Cache the MSR value to avoid reading it later */ >> @@ -7307,7 +7307,7 @@ void noinstr vmx_spec_ctrl_restore_host(struct vcpu_vmx *vmx, >> return; >> >> if (flags & VMX_RUN_SAVE_SPEC_CTRL) >> - vmx->spec_ctrl = __rdmsr(MSR_IA32_SPEC_CTRL); >> + vmx->spec_ctrl = native_rdmsrq(MSR_IA32_SPEC_CTRL); > > And what guarantees that native_rdmsrq() won't have tracing? Ugh, a later patch > renames native_rdmsrq() => native_rdmsrq_no_trace(). > > I really don't like this. It makes simple and obvious code: > > vmx->spec_ctrl = __rdmsr(MSR_IA32_SPEC_CTRL); > > so much harder to read: > > vmx->spec_ctrl = native_rdmsrq_no_trace(MSR_IA32_SPEC_CTRL); > > and does so in a way that is difficult to review, e.g. I have to peek ahead to > understand that this is even ok. > > I strongly prefer that we find a way to not require such verbose APIs, especially > if KVM ends up using native variants throughout. Xen PV is supposed to be the > odd one out, yet native code is what suffers. Blech. Will try to figure out how to name the APIs. One reason I chose verbose names is that short names are in use and renaming needs to touch a lot of files (and not fun at all). Thanks! Xin