From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f47.google.com (mail-wr1-f47.google.com [209.85.221.47]) (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 CCC1E31E848 for ; Fri, 19 Jun 2026 15:06:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.47 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781881610; cv=none; b=h3PTEWzE1jQ0LlQ5fl+Jq52a4pqOiGS6NIRRBTmD1DC87sA1WqH21IeNIebhsEwXfv8kK4FJnD8j+4eC3RhlFfzBbvdtMUA9zBKLtHokSyMHbV7S+g1rn9E0px4bnq6VfrYO+RlzFL2Sdk8+ZD64koiCA3KH99tuMEZfTbKjDBg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781881610; c=relaxed/simple; bh=6pKJbGXD3BjzZ6jiJgE2wbpszsCFCKqrbr9eZJ+4bJI=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=a2BPEA+emLFYc9oXkItv2NP0PezyHywH1Wnsmq9UcH2qFzJNGtMytcETYmhJUQM86W7f5nCSFqhI/ERQOWwgQFapgbH2DpBjPG1mK3fPyIKtzZKr/mxnVhaTcSbuS+JdSICpRtKQ0pxlpWydiFcB47EaRP7f5OHBhIYrcUZk/pE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=ml5PIyXh; arc=none smtp.client-ip=209.85.221.47 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ml5PIyXh" Received: by mail-wr1-f47.google.com with SMTP id ffacd0b85a97d-45fe59255beso1228947f8f.1 for ; Fri, 19 Jun 2026 08:06:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1781881607; x=1782486407; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=E5kDXUnyJJXjz/qiqqJglYFwJpL0mExjzODZMSDh1B8=; b=ml5PIyXhow2fCugjtwMLgU11fcd5bblay2/DgtT+1CODVIBs5aRxXlnE6nfh3J2qup rQKY+poOgZhKmNGa3W9cDzJWOPIZhE3AkSZ88L9y+6SVWjfBdpLd69HG6O2P70ZW6Nuh o6AascNR2h5VnSDkoNBNrP47+SEXgJxn9SstXN+7U0YOeX8A1J4CByEhKd5on/wr3Yuv nheJQqumv7GENKqVsy2MHofZ5E25dzKVOp5vH/H5UQsoHnP+NAOPQGZciCtq0UDMyBr7 la/kLxMX1s6WLnTOSE7mQzblr97QVeNF5FJm/vM9aNZ+zlNefR5jjBtviHNmd0/M92lh sVUA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1781881607; x=1782486407; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=E5kDXUnyJJXjz/qiqqJglYFwJpL0mExjzODZMSDh1B8=; b=fbW8DMnw1jj/1DMvd+RrKoqsYtBEmHFKLQ9SPQa/MDG60tdI75o9t+0iy+bT+KoYb/ cnjBoF/M5W0kYsWyi1AGXvA5J5e748r7Vp7T2tkcWRStTJYLnnFIPg5j0GRWxcTLNfs/ 5dPW3kHvTF5Cd0MO8wua7lXNybMlAdHUmJ+jTp4NunK53G06vAbafI3LN2VHCLlfqUSf D3b4P6rHPZaOEAkBv+6zqQ3onuhkNTS1pNL5HNm5LOamtZSiLL8IRhLE6s/MlqqPcCDu qXUuy/f6RfsZ6EDYGBPXUxUtvpN35LuI9yg2APBoT/Myzm8dnLBgp1Ww/GyzhzgyRfXA EfTw== X-Forwarded-Encrypted: i=1; AFNElJ9i4ZmATJNpiX4TTvvEXsL1RPkCAtb1ALbfEwfsF4YnNoU9xKhqKBQKJF155AVbm27GLMKRVPWqF9OPKbo=@vger.kernel.org X-Gm-Message-State: AOJu0YwEfwcf7RgbVpTW/zKXYNM7oURPQTlxbv0EHDHQTBnANCsZa/eU EEYcmITVDYJrHuhpDVNJ/GdRRsQvbAVmzQpGAnUmp1NEKhmk5ur6uHbK X-Gm-Gg: AfdE7cmlC5b0QKIDdQRKJ1dPNEBBMbRAC2kRtyxAusBc79T8V5NfT2N7+iqEYTvom/a 4Ttx/MNedODRKMlbmGvni2Mh9vxNO4uR8/K9OosblRHtzywTX6TwcTV0g0HpsBe9fNgfJ5bsyFu EEcqxCSexW0qW+t4n72aFYiTmSw+Jq4nFrcouxbTBWrvz1FYQAKi2MUB6UFFupADu3lNGY0mAq/ EUi84CEURuV3Sb7WSG0L7dHOPA/cqKFwuyGTjzkSde40DYUh9mw3Az3ZnOdYs1A+pY3abn9Uubq syaJFjly2r/yiVzOCU0vA8zquuhGg8facjJHZXbAo3NAFN8ktdcEQ6m7yTToAv7ROejvpdnvopl 4edtWkxp8I6MEicGquHt5KrVnRrLEOI27jSrgBxhiAsLfnK1b5dYFX8dQo1edsyadRP3niIsyL0 BVn2vwKfwH/s9h527fAsyUs16Ppozf7lil/Iq1yls99Mk+mzrTbQ== X-Received: by 2002:a5d:5f96:0:b0:462:d07e:4bc4 with SMTP id ffacd0b85a97d-4656d643ccamr4620478f8f.7.1781881607111; Fri, 19 Jun 2026 08:06:47 -0700 (PDT) Received: from pumpkin (82-69-66-36.dsl.in-addr.zen.co.uk. [82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-46508a0473bsm10004425f8f.1.2026.06.19.08.06.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Jun 2026 08:06:46 -0700 (PDT) Date: Fri, 19 Jun 2026 16:06:45 +0100 From: David Laight To: Sean Christopherson Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: x86: Replace BUG_ON() with WARN_ON_ONCE() on "bad" nested GPA translation Message-ID: <20260619160645.57f4e325@pumpkin> In-Reply-To: <20260618185746.2023283-1-seanjc@google.com> References: <20260618185746.2023283-1-seanjc@google.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 18 Jun 2026 11:57:45 -0700 Sean Christopherson wrote: > If KVM attempts to translate what it thinks is an L2 GPA with a non-nested > MMU, simply WARN and return the GPA, i.e. trust the MMU more than the > caller, as there is zero reason to potentially panic the host kernel just > because KVM misused an API. Except that PANIC_ON_WARN stands a reasonable chance of being set. So it makes little difference. David > > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/svm/nested.c | 3 ++- > arch/x86/kvm/vmx/nested.c | 3 ++- > 2 files changed, 4 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c > index 9aedb88c832d..3e6c671a8dc2 100644 > --- a/arch/x86/kvm/svm/nested.c > +++ b/arch/x86/kvm/svm/nested.c > @@ -2152,7 +2152,8 @@ static gpa_t svm_translate_nested_gpa(struct kvm_vcpu *vcpu, gpa_t gpa, > struct vcpu_svm *svm = to_svm(vcpu); > struct kvm_mmu *mmu = vcpu->arch.mmu; > > - BUG_ON(!mmu_is_nested(vcpu)); > + if (WARN_ON_ONCE(!mmu_is_nested(vcpu))) > + return gpa; > > /* Non-GMET walks are always user-walks */ > if (!(svm->nested.ctl.misc_ctl & SVM_MISC_ENABLE_GMET)) > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c > index 3a293640d58c..6957bb6f5cf7 100644 > --- a/arch/x86/kvm/vmx/nested.c > +++ b/arch/x86/kvm/vmx/nested.c > @@ -7470,7 +7470,8 @@ static gpa_t vmx_translate_nested_gpa(struct kvm_vcpu *vcpu, gpa_t gpa, > { > struct kvm_mmu *mmu = vcpu->arch.mmu; > > - BUG_ON(!mmu_is_nested(vcpu)); > + if (WARN_ON_ONCE(!mmu_is_nested(vcpu))) > + return gpa; > > /* > * MBEC differentiates based on the effective U/S bit of > > base-commit: 9d4853b044beefa21c4ee3e18c40653601a64ced