From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f44.google.com (mail-wr1-f44.google.com [209.85.221.44]) (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 F3E0F2853F3 for ; Fri, 19 Jun 2026 15:06:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.44 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781881610; cv=none; b=LW+Yha1hSyESpr31rqkhYGd+3WrI35vSdfLq6m4e1PPy83vig30TgT2C0n5kH6H4id6e6j+Z83FaeLhFzd/BbLXpmrgc9l/mdNHrQiweLUDNreKU6jA+EdbuHbxbteknUnP2nV/3o2ld+nU3TIZEJua2u7rogqHthyHxhzQ/Tq0= 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=209.85.221.44 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-f44.google.com with SMTP id ffacd0b85a97d-4601949975dso372728f8f.0 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=iP9yrvKyXk3NMLzjPdjiNYpwJFRYwvOSZTxnvT8HRg3Ol4EJTnlFW6d8mWLC1H67CQ tidV3g36YwYrY816Hew0o/68kAIoEkndBB2PdYhCOl2yxi1ucqAmrlLo43OgJDAgpot6 xA2Xray3aubB0e2eFemMmSzOxP16cD2Jhj6s0GtePJGm2oTwofedmQYiyJase6Jf50lX /W/jUuXZW8iFyANsfsfQHhY/lEA4lKXjgBG5JLitiP49mHGQ5Uhg7sDoyuPcqTdESxm2 iuB52NFSAkKSvbsLgLBIY+miGSxNpuYQdbU+IULgyRSw9fnNmosngaIvUhHU91Lvccj9 CP3w== X-Forwarded-Encrypted: i=1; AFNElJ92pl9Vy4mneenycgJvcGG1udUgn0K92Z6Ncif0vsiTIr4zKtVJF+6knoiOXImgfiNPzZk=@vger.kernel.org X-Gm-Message-State: AOJu0Yw88sw/sh1SNgLkk/BJ1kznv28reSBxl/YIWHPpg8UgFQF6sE1o uzPT0gY5X7YjXKp/1oCWWf5JZ6i+SjsHEVCkxobqJD42ZnJR45V8cvpX X-Gm-Gg: AfdE7clkolNFFmLKdbhKmKDppote8ZaFD7clSirKkYM+JVL1hIYEHIJoVLAjBYW7VjV xm6sFQhQEvn7AzH9ZmlCMVcS2pOW/IsTVt1RbbcsxZz0CPoX4BZRblIT8goyLLVK7+k1DJ+Vu5c pvD6f3bUPzHxqxxxU8QY+Rj+4JSE7N0dJe5DD4hA2pgZ+yDH6XZ+SOqt9V0iQnEbjzYmWnhBIUT dhlCET1bZA54pljE64eo91dApR4iC9StZCpQ7zXCv33o/247YSnWguCgwk71/EjTiJXpFGdldVS lyIqouFYgNaTdxDEsYyPNR06FPl9WnmpErOtO+6mQy8hqEgGQgK6r4ts6zGl3hrYuxqH8r41lpv 0FKUW0uaUiQYTJxT8eCS7yP3u6zLsz7ciONWpe2nE9cIVshPSOpiaqPeiS/qXvHGDVa8Ytl3OSy tUc5Ny7F26p4e7icWXo2r34lQuSh2vpxGBu4Rt0RCVWPECE0ezLQ== 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: kvm@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