From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f201.google.com (mail-pf1-f201.google.com [209.85.210.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5037D1384B6 for ; Mon, 3 Jun 2024 23:43:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717458181; cv=none; b=O/3I8QtlAKsmSvYi82Mp567Iv5VHzfb4glq+5NAxYRCwyYAXFUWXTlkq82qnehvWAsUH8P1oYCO8pj7QSTFNm0n5BPC6DaE68E7/Acz24VPrnCr3KuqMscKZ+3j+4qYDlMnW14pseEfe+0TBN99s7VtO8wqviLbRZDJHosj/tgQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717458181; c=relaxed/simple; bh=V3fEIuQymV976CLe41KoEQSFCwFNlwcObBa1MX7WNZM=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=CUjxVqXtQ0YZAXS6bAwqJcDvuM2PIXq5qU0FQiGt6IacgFITEFt+t9uG/9O8PSV+2NjIOQs1LIKgwSXzaShP0mKCuTDWAPhX4BYbmpXZdExEVvH7PcP64qNwRK1efbj7BrYpcSMFmykCMMH+S7NPjvUuZuI7glh2pkBsK4jaMPs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=hYd2cOdp; arc=none smtp.client-ip=209.85.210.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="hYd2cOdp" Received: by mail-pf1-f201.google.com with SMTP id d2e1a72fcca58-702543bf7bbso2858312b3a.2 for ; Mon, 03 Jun 2024 16:43:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1717458180; x=1718062980; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=Ix1wBJXtB+Dz1uENt+vCOboXGMIz++QIsMDaGY5XcG0=; b=hYd2cOdpnCzmLdJLRRINBKE9ll/K0coq7EHE01h2Kr7JbF0I7lp7qVDOyu2jYXl3Vc 4HWppem3GP2StIs0KtnUNVN0Nw7AASYRN08pheXyVX90hM5sc1DNxxAwrneiFF7EXQIF 3U0VmiusJiuzZMe0lBnemMDPG/yW34VEM6qpW3Q29bvv0WPnu3q0UhTGLkLjQa4ULAj4 oIJs56oGOn9PaPUYf1MV7u0uG6ugHHkCG53/TAyTTkx6Ec3YJloky1d6Cik7ocZd9Yqi 5Yv2zBM/ulvMXm5MI91wm3Y69czS10eLIuvChTXz/h7I3sYgG5grRI+RTynx2GRdsQk+ 9LBw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1717458180; x=1718062980; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=Ix1wBJXtB+Dz1uENt+vCOboXGMIz++QIsMDaGY5XcG0=; b=kkAd4esnQxk7/gyNSJHJg/oorP/ce13cBwysZg0/0Mdxk8QJXpF2lfA2QttXj3qZQW FzmFuu0wa51fl8dWmY1j/gU1kXJuvajAXY+9bKopNDNmvpVsKcrNpiuMNTAcTnEpgskt dF4e+nAFo6Cqk7oRdUkB8qKKxGUdVduU+6lFsyGo5eNdNo6UeLpkPjdz0mZGDm6BuF4r JetHttQ2VdsUGhZTSFjyNP3zgexXZtzBUtD6paFiVnCjaE0uzuK8axRGbS/h9PNUygKB yTrXLGxE3DLJB+uiSiP+j7NMyYRyoUcV7op/X7ZrXFPFE8CO3Qv5UppDHMp4Qm7mzWv6 lc4g== X-Forwarded-Encrypted: i=1; AJvYcCWCA7g0SG5A87r6AndUS9AR/aQBrCqqKYMbVhCZqcdyQzpT6ZMVDzS/uew+7TGwYGgTgYr+7BFJdMeOZW3njm20yLac X-Gm-Message-State: AOJu0YzOwTCHNPhNUAZckWU0NRrd9FQ6gxrhALSnKqbuz4pw9wkODENI A4w1GJZzCoLzOO1oLRDjPCwMEauMtyb56PVryQ6O9UaSK599A/yMhZ/g4eJZejUL0I0gqY1IGrD WuQ== X-Google-Smtp-Source: AGHT+IHqaNu096+Zwzp8CVw1P6SzEE6P0P87czRc7jhnRB8aCHCFmhBfG3lGqTDH2L6pdWw4pe0K6jzFHnw= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6a00:847:b0:6f4:47dd:5f41 with SMTP id d2e1a72fcca58-70247a9eb6bmr511116b3a.6.1717458179407; Mon, 03 Jun 2024 16:42:59 -0700 (PDT) Date: Mon, 3 Jun 2024 16:42:57 -0700 In-Reply-To: <20240503142548.194585-1-wei.w.wang@intel.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240503142548.194585-1-wei.w.wang@intel.com> Message-ID: Subject: Re: [PATCH v1] KVM: x86: 0-initialize kvm_caps.supported_xss on definition From: Sean Christopherson To: Wei Wang Cc: pbonzini@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Fri, May 03, 2024, Wei Wang wrote: > 0-initialize kvm_caps.supported_xss on definition, so that it doesn't > need to be explicitly zero-ed either in the common x86 or VMX/SVM > initialization paths. This simplifies the code and reduces LOCs. Heh, nope, see commit 40269c03fdbf ("KVM: x86: Explicitly zero kvm_caps during vendor module load"). I do agree the code in kvm_x86_vendor_init() in particular is a bit odd, but it's there because KVM support for XSAVES could be cleared by ->hardware_setup() (XSAVES has a VMX knob, XSAVE for XCR0 does not). And while I agree it's also odd that vendor code explicitly zeros supported_xss, that too serves a purpose. It reduces the probability of advertising XSS support in vendor code that doesn't yet fully support the feature, e.g. if KVM VMX supports CET before KVM SVM, then KVM SVM "needs" to clear supported_xss. In quotes because common KVM should also do the clearing based on CET CPUID features. But, it's still a nice reminder that vendor code likely needs additional support. > No functional changes intended. > > Signed-off-by: Wei Wang > --- > arch/x86/kvm/svm/svm.c | 1 - > arch/x86/kvm/vmx/vmx.c | 2 -- > arch/x86/kvm/x86.c | 4 +--- > 3 files changed, 1 insertion(+), 6 deletions(-) > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index 9aaf83c8d57d..8105e5383b62 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -5092,7 +5092,6 @@ static __init void svm_set_cpu_caps(void) > kvm_set_cpu_caps(); > > kvm_caps.supported_perf_cap = 0; > - kvm_caps.supported_xss = 0; > > /* CPUID 0x80000001 and 0x8000000A (SVM features) */ > if (nested) { > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 22411f4aff53..495125723c15 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -7952,8 +7952,6 @@ static __init void vmx_set_cpu_caps(void) > if (vmx_umip_emulated()) > kvm_cpu_cap_set(X86_FEATURE_UMIP); > > - /* CPUID 0xD.1 */ > - kvm_caps.supported_xss = 0; > if (!cpu_has_vmx_xsaves()) > kvm_cpu_cap_clear(X86_FEATURE_XSAVES); > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 91478b769af0..6a97592950ff 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -94,6 +94,7 @@ > > struct kvm_caps kvm_caps __read_mostly = { > .supported_mce_cap = MCG_CTL_P | MCG_SER_P, > + .supported_xss = 0, > }; > EXPORT_SYMBOL_GPL(kvm_caps); > > @@ -9795,9 +9796,6 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops) > > kvm_register_perf_callbacks(ops->handle_intel_pt_intr); > > - if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES)) > - kvm_caps.supported_xss = 0; > - > #define __kvm_cpu_cap_has(UNUSED_, f) kvm_cpu_cap_has(f) > cr4_reserved_bits = __cr4_reserved_bits(__kvm_cpu_cap_has, UNUSED_); > #undef __kvm_cpu_cap_has > > base-commit: 16c20208b9c2fff73015ad4e609072feafbf81ad > -- > 2.27.0 >