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 ED383224F0; Tue, 3 Dec 2024 04:10:56 +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=1733199058; cv=none; b=uP6DqtJBrMfJwphOpoJX45JeOsYmOw5pvWRrlWc9zuM+KByMpvWfwd5sLKSAtOWI0MSHAXWzjKHuf1pPsBBh2wRxHHA5y8j/iogGkZHm9QH797qTU0m1v9TXGCWi+WnoZlcI4ZpF3hNQEdGIgQ8D5lDRpows5qU63xhY7XdnqxM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733199058; c=relaxed/simple; bh=ZS7LsGI2ul6edG42PbeSQS1Vzo9+Aq9rtIMK9K3/9jw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=oMDPggJmslILiGoC7z9ALQv4m1iMo8YcaIw23YmxHY3oQxM4e1wUDZ4F017gD+ZeyoUOxLJvp4381dgswNOwYxj6mOh11WqFoNpOZiE2Vy7StleYRqL2tRrTD8GrklJmn0MmruzA7noQ9kqP9nSEv43stbN+S2/JmvpGtZvddfg= ARC-Authentication-Results:i=1; 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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=RDSHn9YgbMj/SGP9f25WYjgOkPbspINuSTcqQC3Xn+QMx9ncZZeAsFmGs09JHNZtN 6IeBjOt9WIiegvHcSkw/6rp+CwdoraHSEI8mISCic+C6z7LhE6UEIUMC9fjJJPpL3u dU7IxTRlEhh73Pwh1BsbLXECyGA7jocz2SR47GxukMlxWavs5sH9kGA/dcrqNggUAA /1X4gR402tHq67Cb5GPgcMexk9W8p63VCgtmRZGkc4STwEneVaK/sdxH8ZiszXd2iu 6dm3uvrouJ8CeaUYvDMH3hAJtNISHNOO2X0feQTYDC1eCHKD4CzX/oROXoD6QksjbP j4ykXHguONibg== Message-ID: Date: Mon, 2 Dec 2024 20:09:49 -0800 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 1/2] x86, lib, xenpv: Add WBNOINVD helper functions To: Kevin Loughlin , Andrew Cooper Cc: linux-kernel@vger.kernel.org, seanjc@google.com, pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, kvm@vger.kernel.org, thomas.lendacky@amd.com, pgonda@google.com, sidtelang@google.com, mizhang@google.com, virtualization@lists.linux.dev, xen-devel@lists.xenproject.org, bcm-kernel-feedback-list@broadcom.com References: <20241203005921.1119116-1-kevinloughlin@google.com> <20241203005921.1119116-2-kevinloughlin@google.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 12/2/2024 5:44 PM, Kevin Loughlin wrote: > On Mon, Dec 2, 2024 at 5:28 PM Andrew Cooper wrote: >> >> On 03/12/2024 12:59 am, Kevin Loughlin wrote: >>> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h >>> index d4eb9e1d61b8..c040af2d8eff 100644 >>> --- a/arch/x86/include/asm/paravirt.h >>> +++ b/arch/x86/include/asm/paravirt.h >>> @@ -187,6 +187,13 @@ static __always_inline void wbinvd(void) >>> PVOP_ALT_VCALL0(cpu.wbinvd, "wbinvd", ALT_NOT_XEN); >>> } >>> >>> +extern noinstr void pv_native_wbnoinvd(void); >>> + >>> +static __always_inline void wbnoinvd(void) >>> +{ >>> + PVOP_ALT_VCALL0(cpu.wbnoinvd, "wbnoinvd", ALT_NOT_XEN); >>> +} >> >> Given this, ... >> >>> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c >>> index fec381533555..a66b708d8a1e 100644 >>> --- a/arch/x86/kernel/paravirt.c >>> +++ b/arch/x86/kernel/paravirt.c >>> @@ -149,6 +154,7 @@ struct paravirt_patch_template pv_ops = { >>> .cpu.write_cr0 = native_write_cr0, >>> .cpu.write_cr4 = native_write_cr4, >>> .cpu.wbinvd = pv_native_wbinvd, >>> + .cpu.wbnoinvd = pv_native_wbnoinvd, >>> .cpu.read_msr = native_read_msr, >>> .cpu.write_msr = native_write_msr, >>> .cpu.read_msr_safe = native_read_msr_safe, >> >> this, and ... >> >>> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c >>> index d6818c6cafda..a5c76a6f8976 100644 >>> --- a/arch/x86/xen/enlighten_pv.c >>> +++ b/arch/x86/xen/enlighten_pv.c >>> @@ -1162,6 +1162,7 @@ static const typeof(pv_ops) xen_cpu_ops __initconst = { >>> .write_cr4 = xen_write_cr4, >>> >>> .wbinvd = pv_native_wbinvd, >>> + .wbnoinvd = pv_native_wbnoinvd, >>> >>> .read_msr = xen_read_msr, >>> .write_msr = xen_write_msr, >> >> this, what is the point having a paravirt hook which is wired to >> native_wbnoinvd() in all cases? >> >> That just seems like overhead for overhead sake. > > I'm mirroring what's done for WBINVD here, which was changed to a > paravirt hook in 10a099405fdf ("cpuidle, xenpv: Make more PARAVIRT_XXL > noinstr clean") in order to avoid calls out to instrumented code as > described in the commit message in more detail. I believe a hook is > similarly required for WBNOINVD, but please let me know if you > disagree. Thanks! Then the question is why we need to add WBINVD/WBNOINVD to the paravirt hooks.