From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [134.134.136.31]) (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 70B5BF9D5 for ; Thu, 17 Aug 2023 23:14:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1692314074; x=1723850074; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=HPtftuttc3nnrGELFH+bHrdAFWcXr46RVKvnOFRQIDI=; b=ghrd9sE6inxB6eL9YzTov5N9008en5IYqEXlCZElxp5GXLLlH7JoPRs+ EYgG8OQf4QdySY6kRwk+qPPI0PBI2CuUVYjSBDNwNqInf/R6nE2U0ecx2 2DP7sH/ImmDuQ7sSB9/N6WOMoE4AiiexDbXlWGMXy8YiCibtiofoaRC9t Msm5nXHGOPQrcoTV3HWzRlSx060b4wDm20WBVPWYfWSj+SEUztPf4hfG7 DKfSjSD9U/TpdzEMBffTGWe2tycJ6sLz6YEdMSZ3ADMBCYkHCN/+IU6JS V2tfMpO/+7m68LpmHarjw9bKhcViLHxCmq1cgBQsNJpT6PamBxCwcHskK Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10805"; a="436872060" X-IronPort-AV: E=Sophos;i="6.01,181,1684825200"; d="scan'208";a="436872060" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Aug 2023 16:14:33 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10805"; a="824863019" X-IronPort-AV: E=Sophos;i="6.01,181,1684825200"; d="scan'208";a="824863019" Received: from lacoffin-mobl.amr.corp.intel.com (HELO [10.212.196.192]) ([10.212.196.192]) by fmsmga003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Aug 2023 16:14:31 -0700 Message-ID: <0d18816a-c46e-ac7e-b98f-ef3dba1c356e@intel.com> Date: Thu, 17 Aug 2023 16:14:32 -0700 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v2 02/15] mshyperv: Introduce hv_get_hypervisor_version function Content-Language: en-US To: Nuno Das Neves , 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> From: Dave Hansen In-Reply-To: <1692309711-5573-3-git-send-email-nunodasneves@linux.microsoft.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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. 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.