From nobody Sun Feb 8 23:04:19 2026 Received: from out-178.mta0.migadu.com (out-178.mta0.migadu.com [91.218.175.178]) (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 1EC442798EA for ; Thu, 15 Jan 2026 01:14:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.178 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768439655; cv=none; b=Yodoy1sfGvRpY1/h1phGM5HmAsLa+DUqth5FEvFYjBxiFViBBxPB7qQ4xIFPOcKK5RalpkW1LznB9OWk/lDgEMh0OBwYMrmL7S+/fKk8ZNylMiip/cGJRAf6P7ZMZNH8zQiu1lguOHEq30MUOFq6g/pHDvwMJSas8nVbfIs0pdM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768439655; c=relaxed/simple; bh=UVpG+EowREj/Awus5qFoFw4/iJjJS9YFFtLxBIvxXkM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OROTxY7nbaUEnAY2vR0w5T9WudVkvrNHpIT9NI1vYpqwFvBSA9rORcHl6MX6WtA/C7+QOi49wnITBJBLPHYgLSsJYXo4EZy5wmnT5NfVREBUooD2t2qZy1kUGThVegmAL4TbUgAKMuUSG4QuEBPTHE0N4lgnC3jU82Mb1t7dGQ0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=LxWrpQ9X; arc=none smtp.client-ip=91.218.175.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="LxWrpQ9X" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1768439652; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6ldoCItHVLee7RyUR5hi7FAn/d6Xlp6dLDsYhKHH3XQ=; b=LxWrpQ9XUl9FttggHFtQ2DYhNp+ZOR2KUSQotMhpunpoxMut278NYtUHMlMBc7Maf9xNBu QkiKLVEdSeNk3J9qeFQ8nQD+fipOski4fAW5LXRrnN+Dgj/cxt8o5GNNPB4zIFUyXbkov5 NLzCa2MvBjtD6UmULJfN8it4iPPnzA8= From: Yosry Ahmed To: Sean Christopherson Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Yosry Ahmed , Jim Mattson Subject: [PATCH v4 26/26] KVM: nSVM: Only copy NP_ENABLE from VMCB01's misc_ctl Date: Thu, 15 Jan 2026 01:13:12 +0000 Message-ID: <20260115011312.3675857-27-yosry.ahmed@linux.dev> In-Reply-To: <20260115011312.3675857-1-yosry.ahmed@linux.dev> References: <20260115011312.3675857-1-yosry.ahmed@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" The 'misc_ctl' field in VMCB02 is taken as-is from VMCB01. However, the only bit that needs to copied is NP_ENABLE, as all other known bits in misc_ctl are related to SEV guests, and KVM doesn't support nested virtualization for SEV guests. Only copy NP_ENABLE to harden against future bugs if/when other bits are set for L1 but should not be set for L2. Opportunistically add a comment explaining why NP_ENABLE is taken from VMCB01 and not VMCB02. Suggested-by: Jim Mattson Signed-off-by: Yosry Ahmed --- arch/x86/kvm/svm/nested.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index e62fd6524feb..b3a90ff262d5 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -856,8 +856,16 @@ static void nested_vmcb02_prepare_control(struct vcpu_= svm *svm, V_NMI_BLOCKING_MASK); } =20 - /* Copied from vmcb01. msrpm_base can be overwritten later. */ - vmcb02->control.misc_ctl =3D vmcb01->control.misc_ctl; + /* + * Copied from vmcb01. msrpm_base can be overwritten later. + * + * NP_ENABLE in vmcb12 is only used for consistency checks. If L1 + * enables NPTs, KVM shadows L1's NPTs and uses those to run L2. If L1 + * disables NPT, KVM runs L2 with the same NPTs used to run L1. For the + * latter, L1 runs L2 with shadow page tables that translate L2 GVAs to + * L1 GPAs, so the same NPTs can be used for L1 and L2. + */ + vmcb02->control.misc_ctl =3D vmcb01->control.misc_ctl & SVM_MISC_CTL_NP_E= NABLE; vmcb02->control.iopm_base_pa =3D vmcb01->control.iopm_base_pa; vmcb02->control.msrpm_base_pa =3D vmcb01->control.msrpm_base_pa; vmcb_mark_dirty(vmcb02, VMCB_PERM_MAP); --=20 2.52.0.457.g6b5491de43-goog