From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 6D6C9C678DD for ; Thu, 17 Aug 2023 23:44:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To: Subject:MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=rnI2v1nPLKGBlNA8UQs7aOfCabFNntaoqdRHZE61R+I=; b=LHhvyw1dO5ugvG MfqRfdZbG5ZQa+SG9iT9TvnO62C0kDVX3+6pFnDlOsW3wle/TcmbdC9IDmnzEJgv3OlAsnqBImfBC KhN8CzmcdNFTlhnDpyIqgjGfbMSGrBck0HUbltRVx6VjXyDFF8ibaSa2aoGx4Y0kwKLOscUCvMp0p RAIBDScoYvRN+RpPzz4dRO1ixAKshV32tozJBrVZp+Ae9UsGkY4sR53+MmNYurcmJdLe9BZu/Oeup ygBbnQ/dpvRBE8NhsrwajYVlmPF/Rat6uw0vonNIbI6b/OG+2U0QEobHGqi7qqbLLan24ONszpGtZ b2T+rcR+p1CxcX126Xxg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qWmeh-007LCc-2M; Thu, 17 Aug 2023 23:43:55 +0000 Received: from linux.microsoft.com ([13.77.154.182]) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qWmee-007LB1-0a for linux-arm-kernel@lists.infradead.org; Thu, 17 Aug 2023 23:43:53 +0000 Received: from [10.16.85.5] (unknown [131.107.8.5]) by linux.microsoft.com (Postfix) with ESMTPSA id 1B4BF211F7BF; Thu, 17 Aug 2023 16:43:50 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 1B4BF211F7BF DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1692315830; bh=SvpYja/c9jhYTVgBr6bqBPMX6EwsdHtUjssCTNc905I=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=n54pAAluDm4ITp73Rwu5QC1UVpr0ytnb154C4vANZa0ThPTwOXUHMGp8stqYQrTo/ 5ZVc3nOqbPxZiRy0C/mguB8JIF8Wx5Wzl32jAMcquOFhnTHjFLQG76pw37YL7j4Ol4 5k0v96Q76WcxGyqavWhYM24cLUTMvDeN4oNlOab8= Message-ID: Date: Thu, 17 Aug 2023 16:43:49 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 02/15] mshyperv: Introduce hv_get_hypervisor_version function Content-Language: en-US To: Dave Hansen , linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org Cc: patches@lists.linux.dev, mikelley@microsoft.com, kys@microsoft.com, wei.liu@kernel.org, haiyangz@microsoft.com, decui@microsoft.com, apais@linux.microsoft.com, Tianyu.Lan@microsoft.com, ssengar@linux.microsoft.com, mukeshrathor@microsoft.com, stanislav.kinsburskiy@gmail.com, jinankjain@linux.microsoft.com, vkuznets@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, will@kernel.org, catalin.marinas@arm.com References: <1692309711-5573-1-git-send-email-nunodasneves@linux.microsoft.com> <1692309711-5573-3-git-send-email-nunodasneves@linux.microsoft.com> <0d18816a-c46e-ac7e-b98f-ef3dba1c356e@intel.com> From: Nuno Das Neves In-Reply-To: <0d18816a-c46e-ac7e-b98f-ef3dba1c356e@intel.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230817_164352_243285_66B0B765 X-CRM114-Status: GOOD ( 16.97 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 8/17/2023 4:14 PM, Dave Hansen wrote: > On 8/17/23 15:01, Nuno Das Neves wrote: >> +int hv_get_hypervisor_version(union hv_hypervisor_version_info *info) >> +{ >> + hv_get_vpreg_128(HV_REGISTER_HYPERVISOR_VERSION, >> + (struct hv_get_vp_registers_output *)info); >> + >> + return 0; >> +} > ... >> +int hv_get_hypervisor_version(union hv_hypervisor_version_info *info) >> +{ >> + unsigned int hv_max_functions; >> + >> + hv_max_functions = cpuid_eax(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS); >> + if (hv_max_functions < HYPERV_CPUID_VERSION) { >> + pr_err("%s: Could not detect Hyper-V version\n", >> + __func__); >> + return -ENODEV; >> + } >> + >> + info->eax = cpuid_eax(HYPERV_CPUID_VERSION); >> + info->ebx = cpuid_ebx(HYPERV_CPUID_VERSION); >> + info->ecx = cpuid_ecx(HYPERV_CPUID_VERSION); >> + info->edx = cpuid_edx(HYPERV_CPUID_VERSION); >> + >> + return 0; >> +} > > I can't help but notice that the ARM version does *one* call to the > hardware while the x86 version does CPUID four different times, once to > get *EACH* register and throwing away the other three registers each > time. Also recall that CPUID is a big, fat architecturally serializing > instruction. This isn't a fast path, but CPUID is about as slow as you get. > Good point, it is quite wasteful. I just went and checked cpuid.h, and of course there is a generic cpuid() function that can get all 4 at once. I will update it to use this in the next version. Thanks! > Is there any reason you can't just have an x86 version of > hv_get_vpreg_128() that gets the 128 bits bytes of data that comes back > in the 4 CPUID registers? > > That might even let you share some more code. Unfortunately, for some reason the hypervisor only lets you get this data via CPUID on x86_64, and via hypercall - i.e. hv_get_vpreg_128() - on ARM64. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel