From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f72.google.com (mail-pj1-f72.google.com [209.85.216.72]) (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 32F8250B41B for ; Fri, 18 Sep 2026 15:56:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.72 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789746963; cv=none; b=rOcTHmDlsOPJ0VVHoHEqRPXjFXljw2zEbs9syNL8V6E7SgLtW4aTlzYENDN/izjsnRULcw4k3dJ8mgskuTmvW4B5Plm4oleIRZinFAI6aCeVxH8zJYfG/jKFIZxSCVccmqouG7IWktFk0Mq65HO+KkaWa+fxbSCE7nlXo65IIs0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789746963; c=relaxed/simple; bh=VzBIg2DX36nG7X+/n7IlCo2fJMZUGrggpdgEwOAV7I0=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=cqXk14XAvG4dEhRS858SEyjMaAYdzC24w9x87L7Qg9aLc5Zw5AbCQ5vaZG/ve88T2xfEKVVr0l0QjBtfi+cd0Nj6txmmI2IRIs09QY8z0KzNH10jrEjd/xO14pmKL+phJ0n6KRHz+DGSRHljy1JWGc+OeMlQrSYqaWcHR1DBQsw= 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=p2hMNglS; arc=none smtp.client-ip=209.85.216.72 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="p2hMNglS" Received: by mail-pj1-f72.google.com with SMTP id 98e67ed59e1d1-3968bb86fb7so1234073a91.2 for ; Fri, 18 Sep 2026 08:56:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1789746961; x=1790351761; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=iBkctlRBevMkXW3iFcvrG/AH6FpsnkeJtwK+1UWTkNM=; b=p2hMNglSnFx7HTcQKFe5jAbvd0RDevERIaZMchDjV3AmlsWBJJu/N2yL0Skxy8KB26 ei2XPZi9h+A99UmHIPYtRc+/W5P2ADr9G0QzLFoux5P0wEqWs8aX1ww3JoREuFV8p8zl yKlOp+OW3qGNf6rQK4n079oV8pV/HuuznElZxq0atQTA8o2sXmitrRzCShjRGZ+0dEhH TI3odKSDrvLNrXkDvm2waaNNnrGd4H4t6jVsiaWbK9dtanC/xeWDDk79xXHImYOqWYyv WpIiJV2o9bYhDFMu88uyyXuRUvplX6ZnVZmwMrTRGSpUeCnVRnGp2jDXXMuhhS3nAk1n 7GOw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1789746961; x=1790351761; h=content-type: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:content-type; bh=iBkctlRBevMkXW3iFcvrG/AH6FpsnkeJtwK+1UWTkNM=; b=SSCDEL5+F4wIDYA3UpY99OuxHxHKg/4gV9enho5coXlrG6UhVDHsB2RLbTukb+o/rf ufOSkOlSjXTBCRSvkJPIDjpiKiYqTq+Dl4u2Wk36AcIWMSZndhSapKGB6qWvFDvRYa/5 YjsiqyjUcZbGU1NeMr9d3iHnUNFXbgds/9vHu2QFzaLx7ge3wUOpBQ3UneLj4PdgsVrW /sC2HZH4mPGP7P0QM0iec+6l8fPu5aS6hJ6IDLKU0aNsXDQO58I3fzC+9dIk8+UoQ8DR KduCWsk9lJCrFbgONHTLanNtvx56u+3UTXzKaJc8DFRvihoPOHt19jxLHcpHMPjvyxjm wxFg== X-Forwarded-Encrypted: i=1; AKwUvBwXNHCYTjIq8E9XPunLRanUc6sTLeTe1zDHQrL9rSyeWEeT6rClMnmpx4KQEf1Xxanqfvg3E5wbPyCEJH0=@vger.kernel.org X-Gm-Message-State: AFuF++mKqD2fmYNxsiboCaOn1nCJWnOOoowq7vpA+VB38gBMZZUZ8RZe 4VzAIjRAvgcc6SbO6KhzFcPKVJGyMdeYrTYbifR4yowFUDCpxDLh+Uj4PGc2WcldzIMyVAlxNRq 4wjXmeg== X-Received: from pjbpm7.prod.google.com ([2002:a17:90b:3c47:b0:39e:64b2:d2e7]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:50cc:b0:39d:e43c:5a0d with SMTP id 98e67ed59e1d1-39e54ce0f4cmr7161460a91.8.1789746961199; Fri, 18 Sep 2026 08:56:01 -0700 (PDT) Date: Fri, 18 Sep 2026 08:56:00 -0700 In-Reply-To: <20260918154530.4129698-1-jmattson@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260918154530.4129698-1-jmattson@google.com> Message-ID: Subject: Re: [PATCH] KVM: x86: Disallow EFER.LMSLE when EferLmsleUnsupported is set in guest CPUID From: Sean Christopherson To: Jim Mattson Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Nikunj A Dadhania , Yosry Ahmed Content-Type: text/plain; charset="us-ascii" On Fri, Sep 18, 2026, Jim Mattson wrote: > Reject guest writes to EFER (and nested VMRUN with VMCB12 EFER) that set > EFER.LMSLE when CPUID.80000008H:EBX.EferLmsleUnsupported[bit 20] is set > in the guest's CPUID. > > Commit c53c632592a4 ("KVM: SVM: Disallow EFER.LMSLE when not supported by > hardware") prevented EFER.LMSLE from being enabled in supported_efer_bits > on hosts that set EferLmsleUnsupported, but missed checking the guest > CPUID capability in __kvm_valid_efer(). As a result, on a host that > supports EFER.LMSLE (e.g. Rome), a guest whose userspace VMM sets > EferLmsleUnsupported in guest CPUID (e.g. for migration compatibility > with Milan, Genoa, or Turin) can still set EFER.LMSLE without triggering > a #GP. > > Fixes: c53c632592a4 ("KVM: SVM: Disallow EFER.LMSLE when not supported by hardware") > Assisted-by: LLM > Signed-off-by: Jim Mattson > --- > arch/x86/kvm/msrs.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/msrs.c b/arch/x86/kvm/msrs.c > index dd3bb04878ca..6dbaf063cc8d 100644 > --- a/arch/x86/kvm/msrs.c > +++ b/arch/x86/kvm/msrs.c > @@ -598,8 +598,11 @@ static bool __kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer) > if (efer & EFER_NX && !guest_cpu_cap_has(vcpu, X86_FEATURE_NX)) > return false; > > - return true; > + if (efer & EFER_LMSLE && > + guest_cpu_cap_has(vcpu, X86_FEATURE_EFER_LMSLE_MBZ)) > + return false; > > + return true; In case anyone else was wondering, this is NOT whitespace damage, the "movement" of the "return true" is due to deleting a trailing spurious newline, e.g. my configuration of diff yeilds: diff --git a/arch/x86/kvm/msrs.c b/arch/x86/kvm/msrs.c index dd3bb04878ca..6dbaf063cc8d 100644 --- a/arch/x86/kvm/msrs.c +++ b/arch/x86/kvm/msrs.c @@ -598,8 +598,11 @@ static bool __kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer) if (efer & EFER_NX && !guest_cpu_cap_has(vcpu, X86_FEATURE_NX)) return false; + if (efer & EFER_LMSLE && + guest_cpu_cap_has(vcpu, X86_FEATURE_EFER_LMSLE_MBZ)) + return false; + return true; - } bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer) {