From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964794AbdIYM73 (ORCPT ); Mon, 25 Sep 2017 08:59:29 -0400 Received: from mga01.intel.com ([192.55.52.88]:38585 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934840AbdIYM72 (ORCPT ); Mon, 25 Sep 2017 08:59:28 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.42,436,1500966000"; d="scan'208";a="1018116727" Message-ID: <59C8FE6E.7070503@intel.com> Date: Mon, 25 Sep 2017 21:02:38 +0800 From: Wei Wang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Paolo Bonzini , virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mst@redhat.com, rkrcmar@redhat.com, ak@linux.intel.com, mingo@redhat.com Subject: Re: [PATCH v1 1/4] KVM/vmx: re-write the msr auto switch feature References: <1506314696-4632-1-git-send-email-wei.w.wang@intel.com> <1506314696-4632-2-git-send-email-wei.w.wang@intel.com> <7f9d54dd-546a-548f-5425-e4151e09fbdc@redhat.com> In-Reply-To: <7f9d54dd-546a-548f-5425-e4151e09fbdc@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/25/2017 07:54 PM, Paolo Bonzini wrote: > On 25/09/2017 06:44, Wei Wang wrote: >> >> +static void update_msr_autoload_count_max(void) >> +{ >> + u64 vmx_msr; >> + int n; >> + >> + /* >> + * According to the Intel SDM, if Bits 27:25 of MSR_IA32_VMX_MISC is >> + * n, then (n + 1) * 512 is the recommended max number of MSRs to be >> + * included in the VMExit and VMEntry MSR auto switch list. >> + */ >> + rdmsrl(MSR_IA32_VMX_MISC, vmx_msr); >> + n = ((vmx_msr & 0xe000000) >> 25) + 1; >> + msr_autoload_count_max = n * KVM_VMX_DEFAULT_MSR_AUTO_LOAD_COUNT; >> +} >> + > > Any reasons to do this if it's unlikely that we'll ever update more than > 512 MSRs? > > Paolo It isn't a must to allocate memory for 512 MSRs, but I think it would be good to allocate memory at least for 128 MSRs, because on skylake we have 32 triplets of MSRs (FROM/TO/INFO), which are 96 in total already. The disadvantage is that developers would need to manually calculate and change the number carefully when they need to add new MSRs for auto switching in the future. So, if consuming a little bit more memory isn't a concern, I think we can directly allocate memory based on what's recommended by the hardware. Best, Wei