From: Sean Christopherson <seanjc@google.com>
To: Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Yosry Ahmed <yosry@kernel.org>,
Shivansh Dhiman <shivansh.dhiman@amd.com>,
Nikunj A Dadhania <nikunj@amd.com>,
Ravi Bangoria <ravi.bangoria@amd.com>,
Tom Lendacky <thomas.lendacky@amd.com>
Subject: [PATCH v6 04/12] KVM: x86: Force fixed-1 bits in DR6 after synchronizing with hardware
Date: Wed, 30 Sep 2026 12:36:26 -0700 [thread overview]
Message-ID: <20260930193634.3415089-5-seanjc@google.com> (raw)
In-Reply-To: <20260930193634.3415089-1-seanjc@google.com>
Set all fixed-1 bits in KVM's version of DR6 after synchronizing with
hardware to paper over as much of the virtualization hole as possible.
Because KVM dynamically disables DR interception, a guest can write any
DR6 bit that isn't fixed in bare metal, even if the bit is supposed to be
fixed from the guest's perspective.
In addition to providing some amount of consistency in KVM, this will allow
adding sanity checks that KVM never ends up with fixed-1 bits clear in its
version of DR6.
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/regs.c | 2 +-
arch/x86/kvm/regs.h | 1 +
arch/x86/kvm/x86.c | 1 +
3 files changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/regs.c b/arch/x86/kvm/regs.c
index f74a29621661..db43ade8ceb1 100644
--- a/arch/x86/kvm/regs.c
+++ b/arch/x86/kvm/regs.c
@@ -772,7 +772,7 @@ void kvm_update_dr7(struct kvm_vcpu *vcpu)
}
EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_update_dr7);
-static unsigned long kvm_get_dr6_fixed_1(struct kvm_vcpu *vcpu)
+unsigned long kvm_get_dr6_fixed_1(struct kvm_vcpu *vcpu)
{
unsigned long fixed = DR6_FIXED_1;
diff --git a/arch/x86/kvm/regs.h b/arch/x86/kvm/regs.h
index 447f0ec3e63e..3ca5cd8a8d95 100644
--- a/arch/x86/kvm/regs.h
+++ b/arch/x86/kvm/regs.h
@@ -62,6 +62,7 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
int kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8);
int kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val);
unsigned long kvm_get_dr(struct kvm_vcpu *vcpu, int dr);
+unsigned long kvm_get_dr6_fixed_1(struct kvm_vcpu *vcpu);
unsigned long kvm_get_cr8(struct kvm_vcpu *vcpu);
void kvm_lmsw(struct kvm_vcpu *vcpu, unsigned long msw);
int load_pdptrs(struct kvm_vcpu *vcpu, unsigned long cr3);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ea1406c3b260..99518e3265b4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8417,6 +8417,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
WARN_ON(vcpu->arch.switch_db_regs & KVM_DEBUGREG_AUTO_SWITCH);
kvm_x86_call(sync_dirty_debug_regs)(vcpu);
kvm_update_dr0123(vcpu);
+ vcpu->arch.dr6 |= kvm_get_dr6_fixed_1(vcpu);
kvm_update_dr7(vcpu);
}
--
2.56.0.rc1.315.gc6ed9934b7-goog
next prev parent reply other threads:[~2026-09-30 19:36 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-30 19:36 [PATCH v6 00/12] KVM: x86: Bus Lock Detect fixes and SVM support Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 01/12] KVM: x86: Preserve DR6.BLD (Bus Lock Detect) when delivering #DB payload Sean Christopherson
2026-09-30 23:46 ` Shivansh Dhiman
2026-09-30 19:36 ` [PATCH v6 02/12] KVM: x86: Rename kvm_dr6_fixed() => kvm_get_dr6_fixed_1() Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 03/12] KVM: Return an "unsigned long", not "u64" for the fixed-1 DR6 bits Sean Christopherson
2026-09-30 19:36 ` Sean Christopherson [this message]
2026-09-30 19:36 ` [PATCH v6 05/12] KVM: x86: Set guest's fixed-1 DR6 bits when delivering #DB payload Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 06/12] KVM: x86: Kill off DR6_FIXED_1 to prevent future misuse Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 07/12] KVM: SVM: Add helper to query if LBR virtualization needs to be enabled Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 08/12] KVM: nSVM: Disable LBRV in nested control cache when unsupported Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 09/12] KVM: nSVM: Open code check on LBR virtualization being enabled in vmcb12 Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 10/12] KVM: nSVM: Don't assume all active-low bits DR6 are fixed-1 Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 11/12] KVM: SVM: Add a vCPU-aware helper to get supported DEBUGCTL bits Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 12/12] KVM: SVM: Add support for virtualizating Bus Lock Detect Sean Christopherson
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