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 X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7CBADC33C9E for ; Fri, 17 Jan 2020 18:32:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4E0882082F for ; Fri, 17 Jan 2020 18:32:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729148AbgAQScp (ORCPT ); Fri, 17 Jan 2020 13:32:45 -0500 Received: from mga03.intel.com ([134.134.136.65]:14707 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726603AbgAQSco (ORCPT ); Fri, 17 Jan 2020 13:32:44 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 17 Jan 2020 10:31:53 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,331,1574150400"; d="scan'208";a="227299845" Received: from ray.jf.intel.com (HELO [10.7.201.139]) ([10.7.201.139]) by orsmga006.jf.intel.com with ESMTP; 17 Jan 2020 10:31:53 -0800 Subject: Re: [PATCH 1/4] KVM: x86: Handle TIF_NEED_FPU_LOAD in kvm_{load,put}_guest_fpu() To: Sean Christopherson , Paolo Bonzini Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Derek Yerger , kernel@najdan.com, Thomas Lambertz , Rik van Riel , Sebastian Andrzej Siewior , Borislav Petkov , Thomas Gleixner References: <20200117062628.6233-1-sean.j.christopherson@intel.com> <20200117062628.6233-2-sean.j.christopherson@intel.com> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20200117062628.6233-2-sean.j.christopherson@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/16/20 10:26 PM, Sean Christopherson wrote: > Handle TIF_NEED_FPU_LOAD similar to how fpu__copy() handles the flag > when duplicating FPU state to a new task struct. TIF_NEED_FPU_LOAD can > be set any time control is transferred out of KVM, be it voluntarily, > e.g. if I/O is triggered during a KVM call to get_user_pages, or > involuntarily, e.g. if softirq runs after an IRQ occurs. Therefore, > KVM must account for TIF_NEED_FPU_LOAD whenever it is (potentially) > accessing CPU FPU state. > > Fixes: 5f409e20b7945 ("x86/fpu: Defer FPU state load until return to userspace") > Cc: stable@vger.kernel.org > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/x86.c | 27 ++++++++++++++++++++++++--- > 1 file changed, 24 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index cf917139de6b..0c7211491f98 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -8476,8 +8476,20 @@ static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu) > { > fpregs_lock(); > > - copy_fpregs_to_fpstate(vcpu->arch.user_fpu); > - /* PKRU is separately restored in kvm_x86_ops->run. */ > + /* > + * If userspace's FPU state is not resident in the CPU registers, just > + * memcpy() from current, else save CPU state directly to user_fpu. > + */ > + if (test_thread_flag(TIF_NEED_FPU_LOAD)) > + memcpy(&vcpu->arch.user_fpu->state, ¤t->thread.fpu.state, > + fpu_kernel_xstate_size); > + else > + copy_fpregs_to_fpstate(vcpu->arch.user_fpu); > + > + /* > + * Load guest's FPU state to the CPU registers. PKRU is separately > + * loaded in kvm_x86_ops->run. > + */ > __copy_kernel_to_fpregs(&vcpu->arch.guest_fpu->state, > ~XFEATURE_MASK_PKRU); Nit: it took me a minute to realize that there is both: vcpu->arch.user_fpu and vcpu->arch.guest_fpu It might help readability to have local variables for those, or at least a comment to help differentiate the two. > @@ -8492,7 +8504,16 @@ static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu) > { > fpregs_lock(); > > - copy_fpregs_to_fpstate(vcpu->arch.guest_fpu); > + /* > + * If guest's FPU state is not resident in the CPU registers, just > + * memcpy() from current, else save CPU state directly to guest_fpu. > + */ > + if (test_thread_flag(TIF_NEED_FPU_LOAD)) > + memcpy(&vcpu->arch.guest_fpu->state, ¤t->thread.fpu.state, > + fpu_kernel_xstate_size); > + else > + copy_fpregs_to_fpstate(vcpu->arch.guest_fpu); > + > copy_kernel_to_fpregs(&vcpu->arch.user_fpu->state); > > fpregs_mark_activate(); This also makes me wonder if we want to have copy_fpregs_to_fpstate() check for TIF_NEED_FPU_LOAD and complain if it's set.