From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (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 C0DAF286424; Mon, 15 Sep 2025 17:05:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757955915; cv=none; b=WHmEA47to1NhEcRpY6ohhhULM9Inj1v2Qt3vAXiQ7KSjMeK3wqyuEEFCX/+YqvimNWosZNKsM13dwXTDkzWNeuzXBghEEgNym5XrZ3SMF7gEYxii7+rz9xNlexV31+L/jo2pUKgoxZTRfRW3OTCi3UmrfzHCJnHEsYM9zZ/HfpA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757955915; c=relaxed/simple; bh=UYHu4XvkaRjYogwIfNpvwksawDBauQBnyHYV6E8cpTo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=VFNiogxGUpXV5S1zgyUwqw6okGsptCVPsX8P2bMcb1CFyGk0adkp66v0OJaC+LWP82waytil5vJODFlslpy54NzIKze1exhOpxReLdSKXip7P7Zo8PFIYSUxWsiQjtKtv7UV1qCUeDqzPHtLZwZFFn5JgymDEgWBrEbOLMvO1CI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=PswIMUK7; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="PswIMUK7" Received: from [0.0.0.0] ([134.134.137.72]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 58FH4vE22801932 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Mon, 15 Sep 2025 10:04:57 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 58FH4vE22801932 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025082201; t=1757955898; bh=JbWMiStndH0zdL0jqV2oFj5rZ7N3e7IVzr7NBcUkyX0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=PswIMUK7RLrOYL724NWLO+FU07YSavIOCsEN0Lo3+H1kLXvlqoAAziDmyUeHPrE7i 1TLh7s91nbQh/4uA+p7cLa5LY7e9/WOzOLv/2Nb/08l2Nkf5zagSiskgeSrKKXIffS DBjc+m3khQq0wLBsjBMRITk1MaGkH5/Q3SmQt+vHPDYat77jP2m4urEyW5MOL65NoJ wOokMJ2IpYolNK9TWk2lFWPf+d6OaztfznYv/FFdNPZJLHjR4hj8qqnRn8Nx08k6Nr alrKEX9VPXbMUG25G+QZWak9FXaAjpumFnFt0FI8USzG8u9oHbm3C1tGgkfYSYz0M1 JDoRQq0MWQ05g== Message-ID: <65184bb3-0a36-49c3-b212-4b19f2df7092@zytor.com> Date: Mon, 15 Sep 2025 10:04:51 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v15 09/41] KVM: x86: Load guest FPU state when access XSAVE-managed MSRs To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Tom Lendacky , Mathias Krause , John Allen , Rick Edgecombe , Chao Gao , Maxim Levitsky , Xiaoyao Li , Zhang Yi Z References: <20250912232319.429659-1-seanjc@google.com> <20250912232319.429659-10-seanjc@google.com> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; keydata= xsDNBGUPz1cBDACS/9yOJGojBFPxFt0OfTWuMl0uSgpwk37uRrFPTTLw4BaxhlFL0bjs6q+0 2OfG34R+a0ZCuj5c9vggUMoOLdDyA7yPVAJU0OX6lqpg6z/kyQg3t4jvajG6aCgwSDx5Kzg5 Rj3AXl8k2wb0jdqRB4RvaOPFiHNGgXCs5Pkux/qr0laeFIpzMKMootGa4kfURgPhRzUaM1vy bsMsL8vpJtGUmitrSqe5dVNBH00whLtPFM7IbzKURPUOkRRiusFAsw0a1ztCgoFczq6VfAVu raTye0L/VXwZd+aGi401V2tLsAHxxckRi9p3mc0jExPc60joK+aZPy6amwSCy5kAJ/AboYtY VmKIGKx1yx8POy6m+1lZ8C0q9b8eJ8kWPAR78PgT37FQWKYS1uAroG2wLdK7FiIEpPhCD+zH wlslo2ETbdKjrLIPNehQCOWrT32k8vFNEMLP5G/mmjfNj5sEf3IOKgMTMVl9AFjsINLHcxEQ 6T8nGbX/n3msP6A36FDfdSEAEQEAAc0WWGluIExpIDx4aW5Aenl0b3IuY29tPsLBDQQTAQgA NxYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89XBQkFo5qAAhsDBAsJCAcFFQgJCgsFFgID AQAACgkQa70OVx2uN1HUpgv/cM2fsFCQodLArMTX5nt9yqAWgA5t1srri6EgS8W3F+3Kitge tYTBKu6j5BXuXaX3vyfCm+zajDJN77JHuYnpcKKr13VcZi1Swv6Jx1u0II8DOmoDYLb1Q2ZW v83W55fOWJ2g72x/UjVJBQ0sVjAngazU3ckc0TeNQlkcpSVGa/qBIHLfZraWtdrNAQT4A1fa sWGuJrChBFhtKbYXbUCu9AoYmmbQnsx2EWoJy3h7OjtfFapJbPZql+no5AJ3Mk9eE5oWyLH+ QWqtOeJM7kKvn/dBudokFSNhDUw06e7EoVPSJyUIMbYtUO7g2+Atu44G/EPP0yV0J4lRO6EA wYRXff7+I1jIWEHpj5EFVYO6SmBg7zF2illHEW31JAPtdDLDHYcZDfS41caEKOQIPsdzQkaQ oW2hchcjcMPAfyhhRzUpVHLPxLCetP8vrVhTvnaZUo0xaVYb3+wjP+D5j/3+hwblu2agPsaE vgVbZ8Fx3TUxUPCAdr/p73DGg57oHjgezsDNBGUPz1gBDAD4Mg7hMFRQqlzotcNSxatlAQNL MadLfUTFz8wUUa21LPLrHBkUwm8RujehJrzcVbPYwPXIO0uyL/F///CogMNx7Iwo6by43KOy g89wVFhyy237EY76j1lVfLzcMYmjBoTH95fJC/lVb5Whxil6KjSN/R/y3jfG1dPXfwAuZ/4N cMoOslWkfZKJeEut5aZTRepKKF54T5r49H9F7OFLyxrC/uI9UDttWqMxcWyCkHh0v1Di8176 jjYRNTrGEfYfGxSp+3jYL3PoNceIMkqM9haXjjGl0W1B4BidK1LVYBNov0rTEzyr0a1riUrp Qk+6z/LHxCM9lFFXnqH7KWeToTOPQebD2B/Ah5CZlft41i8L6LOF/LCuDBuYlu/fI2nuCc8d m4wwtkou1Y/kIwbEsE/6RQwRXUZhzO6llfoN96Fczr/RwvPIK5SVMixqWq4QGFAyK0m/1ap4 bhIRrdCLVQcgU4glo17vqfEaRcTW5SgX+pGs4KIPPBE5J/ABD6pBnUUAEQEAAcLA/AQYAQgA JhYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89ZBQkFo5qAAhsMAAoJEGu9DlcdrjdR4C0L /RcjolEjoZW8VsyxWtXazQPnaRvzZ4vhmGOsCPr2BPtMlSwDzTlri8BBG1/3t/DNK4JLuwEj OAIE3fkkm+UG4Kjud6aNeraDI52DRVCSx6xff3bjmJsJJMb12mWglN6LjdF6K+PE+OTJUh2F dOhslN5C2kgl0dvUuevwMgQF3IljLmi/6APKYJHjkJpu1E6luZec/lRbetHuNFtbh3xgFIJx 2RpgVDP4xB3f8r0I+y6ua+p7fgOjDLyoFjubRGed0Be45JJQEn7A3CSb6Xu7NYobnxfkwAGZ Q81a2XtvNS7Aj6NWVoOQB5KbM4yosO5+Me1V1SkX2jlnn26JPEvbV3KRFcwV5RnDxm4OQTSk PYbAkjBbm+tuJ/Sm+5Yp5T/BnKz21FoCS8uvTiziHj2H7Cuekn6F8EYhegONm+RVg3vikOpn gao85i4HwQTK9/D1wgJIQkdwWXVMZ6q/OALaBp82vQ2U9sjTyFXgDjglgh00VRAHP7u1Rcu4 l75w1xInsg== In-Reply-To: <20250912232319.429659-10-seanjc@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/12/2025 4:22 PM, Sean Christopherson wrote: > Load the guest's FPU state if userspace is accessing MSRs whose values > are managed by XSAVES. Introduce two helpers, kvm_{get,set}_xstate_msr(), > to facilitate access to such kind of MSRs. > > If MSRs supported in kvm_caps.supported_xss are passed through to guest, > the guest MSRs are swapped with host's before vCPU exits to userspace and > after it reenters kernel before next VM-entry. > > Because the modified code is also used for the KVM_GET_MSRS device ioctl(), > explicitly check @vcpu is non-null before attempting to load guest state. > The XSAVE-managed MSRs cannot be retrieved via the device ioctl() without > loading guest FPU state (which doesn't exist). > > Note that guest_cpuid_has() is not queried as host userspace is allowed to > access MSRs that have not been exposed to the guest, e.g. it might do > KVM_SET_MSRS prior to KVM_SET_CPUID2. > > The two helpers are put here in order to manifest accessing xsave-managed > MSRs requires special check and handling to guarantee the correctness of > read/write to the MSRs. > > Co-developed-by: Yang Weijiang > Signed-off-by: Yang Weijiang > Reviewed-by: Maxim Levitsky > Tested-by: Mathias Krause > Tested-by: John Allen > Tested-by: Rick Edgecombe > Signed-off-by: Chao Gao > [sean: drop S_CET, add big comment, move accessors to x86.c] > Signed-off-by: Sean Christopherson Reviewed-by: Xin Li (Intel) > --- > arch/x86/kvm/x86.c | 86 +++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 85 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index c5e38d6943fe..a95ca2fbd3a9 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -3801,6 +3804,66 @@ static void record_steal_time(struct kvm_vcpu *vcpu) > mark_page_dirty_in_slot(vcpu->kvm, ghc->memslot, gpa_to_gfn(ghc->gpa)); > } > > +/* > + * Returns true if the MSR in question is managed via XSTATE, i.e. is context > + * switched with the rest of guest FPU state. Note! S_CET is _not_ context > + * switched via XSTATE even though it _is_ saved/restored via XSAVES/XRSTORS. > + * Because S_CET is loaded on VM-Enter and VM-Exit via dedicated VMCS fields, > + * the value saved/restored via XSTATE is always the host's value. That detail > + * is _extremely_ important, as the guest's S_CET must _never_ be resident in > + * hardware while executing in the host. Loading guest values for U_CET and > + * PL[0-3]_SSP while executing in the kernel is safe, as U_CET is specific to > + * userspace, and PL[0-3]_SSP are only consumed when transitioning to lower > + * privilegel levels, i.e. are effectively only consumed by userspace as well. > + */ > +static bool is_xstate_managed_msr(struct kvm_vcpu *vcpu, u32 msr) > +{ > + if (!vcpu) > + return false; > + > + switch (msr) { > + case MSR_IA32_U_CET: > + return guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK) || > + guest_cpu_cap_has(vcpu, X86_FEATURE_IBT); > + case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP: > + return guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK); > + default: > + return false; > + } > +} With this new version of is_xstate_managed_msr(), which checks against vcpu capabilities instead of KVM, patch 9 of KVM FRED patches[1] no longer needs to make any change to it. And this is the only conflict when I apply KVM FRED patches on top of this v15 mega-CET patch series. [1] https://lore.kernel.org/lkml/20250829153149.2871901-10-xin@zytor.com/