From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 061E935A940; Fri, 9 Jan 2026 12:21:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767961300; cv=none; b=DIfujyTXHOtTEJgUVkY7zEIwC67/7gir13BK7Sg7KKiiXMhowOuoudPU0s+kv0iT/TD3sJtbNRKlH++cB2bHYp685InKGPfQaCW6KYIglHfFt5fW2iUwvNybJqJcTvgDaDuc2D9eR+8rHTx7GshUFKSE/93FlYo+BkReNSkSsZs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767961300; c=relaxed/simple; bh=vCMssklsHuH5FMddwSdr/g25RnRFLkahil41csLkGBE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Kg/V/X6wLukTgLK4mfMX/RMN8A1Lxbm6p1WuvQ5ruJOlw/2UqHhowo00LHaNhJ14bbXRF5Ag6fa3OYag8hiJk1iB0LXpet1gxuRoCLXK4LvjWwYvDRUXCayf3u7HlBOXGAAENkLPkwYE1TTuYPNrowvz3ksuP5kkXu5SGYzksGU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=D/+Jzg8K; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="D/+Jzg8K" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 84804C4CEF1; Fri, 9 Jan 2026 12:21:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1767961299; bh=vCMssklsHuH5FMddwSdr/g25RnRFLkahil41csLkGBE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=D/+Jzg8KJjpZfOQSazHI7bGngJOFuJJDLSjm7RCi2krHcCTwllsrBcWAxjHgXxj1Y 5vF8kHHHNCGbL0LBz+aTCtJJihjX5OkP9rnDP6nJeT30OgT4s/U2Db0V8XUjaQPywQ yLMgqs4kAmhOhNwNVScwvCOFZbKHnniDLiCi/n7w= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yosry Ahmed , Paolo Bonzini Subject: [PATCH 6.6 703/737] KVM: nSVM: Always recalculate LBR MSR intercepts in svm_update_lbrv() Date: Fri, 9 Jan 2026 12:44:02 +0100 Message-ID: <20260109112200.518591575@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260109112133.973195406@linuxfoundation.org> References: <20260109112133.973195406@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yosry Ahmed commit fbe5e5f030c22ae717ee422aaab0e00ea84fab5e upstream. svm_update_lbrv() is called when MSR_IA32_DEBUGCTLMSR is updated, and on nested transitions where LBRV is used. It checks whether LBRV enablement needs to be changed in the current VMCB, and if it does, it also recalculate intercepts to LBR MSRs. However, there are cases where intercepts need to be updated even when LBRV enablement doesn't. Example scenario: - L1 has MSR_IA32_DEBUGCTLMSR cleared. - L1 runs L2 without LBR_CTL_ENABLE (no LBRV). - L2 sets DEBUGCTLMSR_LBR in MSR_IA32_DEBUGCTLMSR, svm_update_lbrv() sets LBR_CTL_ENABLE in VMCB02 and disables intercepts to LBR MSRs. - L2 exits to L1, svm_update_lbrv() is not called on this transition. - L1 clears MSR_IA32_DEBUGCTLMSR, svm_update_lbrv() finds that LBR_CTL_ENABLE is already cleared in VMCB01 and does nothing. - Intercepts remain disabled, L1 reads to LBR MSRs read the host MSRs. Fix it by always recalculating intercepts in svm_update_lbrv(). Fixes: 1d5a1b5860ed ("KVM: x86: nSVM: correctly virtualize LBR msrs when L2 is running") Cc: stable@vger.kernel.org Signed-off-by: Yosry Ahmed Link: https://patch.msgid.link/20251108004524.1600006-3-yosry.ahmed@linux.dev Signed-off-by: Paolo Bonzini Signed-off-by: Yosry Ahmed Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/svm/svm.c | 29 +++++++++++++++++++---------- 1 file changed, 19 insertions(+), 10 deletions(-) --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -1031,26 +1031,30 @@ static void svm_recalc_lbr_msr_intercept !intercept, !intercept); } -void svm_enable_lbrv(struct kvm_vcpu *vcpu) +static void __svm_enable_lbrv(struct kvm_vcpu *vcpu) { struct vcpu_svm *svm = to_svm(vcpu); svm->vmcb->control.virt_ext |= LBR_CTL_ENABLE_MASK; - svm_recalc_lbr_msr_intercepts(vcpu); /* Move the LBR msrs to the vmcb02 so that the guest can see them. */ if (is_guest_mode(vcpu)) svm_copy_lbrs(svm->vmcb, svm->vmcb01.ptr); } -static void svm_disable_lbrv(struct kvm_vcpu *vcpu) +void svm_enable_lbrv(struct kvm_vcpu *vcpu) +{ + __svm_enable_lbrv(vcpu); + svm_recalc_lbr_msr_intercepts(vcpu); +} + +static void __svm_disable_lbrv(struct kvm_vcpu *vcpu) { struct vcpu_svm *svm = to_svm(vcpu); KVM_BUG_ON(sev_es_guest(vcpu->kvm), vcpu->kvm); svm->vmcb->control.virt_ext &= ~LBR_CTL_ENABLE_MASK; - svm_recalc_lbr_msr_intercepts(vcpu); /* * Move the LBR msrs back to the vmcb01 to avoid copying them @@ -1079,13 +1083,18 @@ void svm_update_lbrv(struct kvm_vcpu *vc (is_guest_mode(vcpu) && guest_can_use(vcpu, X86_FEATURE_LBRV) && (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK)); - if (enable_lbrv == current_enable_lbrv) - return; + if (enable_lbrv && !current_enable_lbrv) + __svm_enable_lbrv(vcpu); + else if (!enable_lbrv && current_enable_lbrv) + __svm_disable_lbrv(vcpu); - if (enable_lbrv) - svm_enable_lbrv(vcpu); - else - svm_disable_lbrv(vcpu); + /* + * During nested transitions, it is possible that the current VMCB has + * LBR_CTL set, but the previous LBR_CTL had it cleared (or vice versa). + * In this case, even though LBR_CTL does not need an update, intercepts + * do, so always recalculate the intercepts here. + */ + svm_recalc_lbr_msr_intercepts(vcpu); } void disable_nmi_singlestep(struct vcpu_svm *svm)