From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f197.google.com (mail-pl1-f197.google.com [209.85.214.197]) (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 14E4F352C5B for ; Wed, 30 Sep 2026 01:13:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.197 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790730806; cv=none; b=JQmlP7l2uhomSlm54zadwuX9yYIU50O6ONuud2VMqfOMv1vloYLXYY++qRwC2kB2Gh5y3iWI9UFqkYobD0lWRJMLowMFUGgARPkIQuBKQ4K1vAyP1GpnXmiQFKtlL+m+gYmkQ2ZkjyJE6ncVnjsjmNa/68Qj8rKrhQiXstU+WZM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790730806; c=relaxed/simple; bh=WJS4SSOV19T6Dt7ROA/A7jK4hLXZXWPr57+NbXRProQ=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=PYd/VgDOeOX83maHTI09wbnnOrFVouSOv6fZ3ynJrUMG2v+VqzxG+y9pTOFIjpSrwA+jTaGGb7Z29C4L4trpVvPPPfqfpwlNEUclQTp8eYuPqYLQ7wPLsnsQBQo8XcHAYZhOxJH8Nyz+r2Sva+RZlb7owIbnFchtwAUdL9PJozU= 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=Y+MFe/jc; arc=none smtp.client-ip=209.85.214.197 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="Y+MFe/jc" Received: by mail-pl1-f197.google.com with SMTP id d9443c01a7336-2cec4226c70so37707345ad.1 for ; Tue, 29 Sep 2026 18:13:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1790730801; x=1791335601; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:reply-to:from:to:cc:subject:date:message-id :reply-to:content-type; bh=aGX1aS7+VbzdnFj570TKAEc3vWnkvcXC0Vr+dYTn8FA=; b=Y+MFe/jcAn0KQjq3QsApAHzXslTOfTVmkNABntEMzZbqzkhrs9JrGFYrrebDvfM1cp 1kb0M4kmGJYVjI3y9eXwkHV3zqoR/2z6KFr2rFCLg3BDA4Z0GE3n7wnAIUgW/HaPhpZn Q7rW+EBTxPGqcU2SBa0gQHDhMu86xvd+GOoBwUgHwkDOtDfF+XRi7brDPenDmqlRyi6x Kb6a/7OTPd7hzqgkjCcUU0jCdUWCO9mDE0rRiDsZXkqxOf0Mbq+cWw5jr5DXFuz+vr2f cTXBQbbMnAES1EdFQLuBHgqv4n1DzkP6dQX2qoV3bBrZIE+V/fp2GZntPLkm37q7AHBi gtuw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1790730801; x=1791335601; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:reply-to:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to:content-type; bh=aGX1aS7+VbzdnFj570TKAEc3vWnkvcXC0Vr+dYTn8FA=; b=GKDxm2oAFbIpXvde6gWyAVnT0JEyLT3+U0ZvZyr6pV2DUj5ozWAkiJjJUHqd0mje04 +oGlcKbgZxHaXCDncrFOHucf7nIg4KRWGM1LfhKWbMYj1VCoyChEptS8eVADGKwALx9/ oUlAfjZz6x0VkvJv5yf86NHPYwZpTl141p0MHxyL5ya6XBHfUt7n9C0rxJQF4KXjLwB3 mWyFMu6E9akb6Q9vfMU3y/KcpIYQXmWmGAFihimCqPTbm8mBtYq8fC7/+Va5smUVkGyZ 2UI1I97hXGnt8QZL6V84wYM+DZb0adZu9zPwOqmB4GmS5vjA1pAg3j8caWt66nYt0VSH nPug== X-Forwarded-Encrypted: i=1; AKwUvBzIr9R9R2YEfzVIwyz0ePyYQKdXToHgLhQuxceY3qd0UoCoYXvbkTk06EQrNsf1mHv5Rg1cId+NKr53SMk=@vger.kernel.org X-Gm-Message-State: AFq9FYIhq1hfLqTcbaWSEBKYWEOk1VwJEaD1hYUkyY5XW6ROpIOxFWkC 6T0m1zjTwBTX4sm/aOt/LpmGAy2atiqEWZpRevgG1qiGWcGoqHEM047QOOw4f12WFQq0R4sR8dA 4DMSSXw== X-Received: from plbg20.prod.google.com ([2002:a17:902:d1d4:b0:2dd:6c51:6e21]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:fc87:b0:2db:5f8c:b81c with SMTP id d9443c01a7336-2e2de52d09fmr6371215ad.19.1790730801141; Tue, 29 Sep 2026 18:13:21 -0700 (PDT) Reply-To: Sean Christopherson Date: Tue, 29 Sep 2026 18:13:06 -0700 In-Reply-To: <20260930011313.3197688-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260930011313.3197688-1-seanjc@google.com> X-Mailer: git-send-email 2.56.0.rc1.315.gc6ed9934b7-goog Message-ID: <20260930011313.3197688-6-seanjc@google.com> Subject: [PATCH v5 05/12] KVM: x86: WARN if fixed-1 DR6 bits aren't already set when delivering payload From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Yosry Ahmed , Shivansh Dhiman , Nikunj A Dadhania , Ravi Bangoria , Tom Lendacky Content-Type: text/plain; charset="UTF-8" WARN if the fixed-1 bits in DR6 aren't already set when delivering a #DB payload, as (stating the obvious) KVM should never clear fixed-1 bits. Opportunistically switch to kvm_get_dr6_fixed_1() instead using the more conservative DR6_FIXED_1, to ensure that bits that are fixed-1 from the guest's perspective are indeed '1'. In practice, this aspect should be a glorified nop specifically because fixed-1 bits should already be set. Signed-off-by: Sean Christopherson --- arch/x86/kvm/x86.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 99518e3265b4..5b3918a4ed52 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -399,7 +399,9 @@ void kvm_deliver_exception_payload(struct kvm_vcpu *vcpu, return; switch (ex->vector) { - case DB_VECTOR: + case DB_VECTOR: { + unsigned long dr6_fixed_1 = kvm_get_dr6_fixed_1(vcpu); + /* * DR6 is a mess. Reserved/unused bits are fixed-to-1, and so * to maintain backwards compatibility with existing software, @@ -426,7 +428,7 @@ void kvm_deliver_exception_payload(struct kvm_vcpu *vcpu, * 2. Clear active-low bits that are present in the payload. * 3. Set active-high bits that are present in the payload. * 4. Clear fixed-0 bits. - * 5. Set fixed-1 bits. + * 5. Sanity check (and set, if necessary) fixed-1 bits. */ vcpu->arch.dr6 &= ~DR_TRAP_BITS; vcpu->arch.dr6 |= DR6_RTM; @@ -440,8 +442,10 @@ void kvm_deliver_exception_payload(struct kvm_vcpu *vcpu, * breakpoint), it is reserved and must be zero in DR6. */ vcpu->arch.dr6 &= ~BIT(12); - vcpu->arch.dr6 |= DR6_FIXED_1; + if (WARN_ON_ONCE((vcpu->arch.dr6 & dr6_fixed_1) != dr6_fixed_1)) + vcpu->arch.dr6 |= dr6_fixed_1; break; + } case PF_VECTOR: vcpu->arch.cr2 = ex->payload; break; -- 2.56.0.rc1.315.gc6ed9934b7-goog