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 v5 06/12] KVM: x86: Kill off DR6_FIXED_1 to prevent future misuse
Date: Tue, 29 Sep 2026 18:13:07 -0700 [thread overview]
Message-ID: <20260930011313.3197688-7-seanjc@google.com> (raw)
In-Reply-To: <20260930011313.3197688-1-seanjc@google.com>
Now that the only user of DR6_FIXED_1 is kvm_get_dr6_fixed_1(), drop the
hardcoded macro to force all references to fixed-1 bits to use the vCPU-
aware helper.
Opportunistically reword the comment about DR6_ACTIVE_LOW to explain why
treating fixed-1 bits as active-low is correct (barring a *very* egregious
architectural goof).
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/regs.c | 2 +-
arch/x86/kvm/regs.h | 10 ++++------
2 files changed, 5 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kvm/regs.c b/arch/x86/kvm/regs.c
index db43ade8ceb1..0c76cf17e884 100644
--- a/arch/x86/kvm/regs.c
+++ b/arch/x86/kvm/regs.c
@@ -774,7 +774,7 @@ EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_update_dr7);
unsigned long kvm_get_dr6_fixed_1(struct kvm_vcpu *vcpu)
{
- unsigned long fixed = DR6_FIXED_1;
+ unsigned long fixed = DR6_ACTIVE_LOW & ~DR6_VOLATILE;
if (!guest_cpu_cap_has(vcpu, X86_FEATURE_RTM))
fixed |= DR6_RTM;
diff --git a/arch/x86/kvm/regs.h b/arch/x86/kvm/regs.h
index 3ca5cd8a8d95..97c17b120a57 100644
--- a/arch/x86/kvm/regs.h
+++ b/arch/x86/kvm/regs.h
@@ -38,16 +38,14 @@ static_assert(!(KVM_POSSIBLE_CR0_GUEST_BITS & X86_CR0_PDPTR_BITS));
#define DR6_BT (1 << 15)
#define DR6_RTM (1 << 16)
/*
- * DR6_ACTIVE_LOW combines fixed-1 and active-low bits.
- * We can regard all the bits in DR6_FIXED_1 as active_low bits;
- * they will never be 0 for now, but when they are defined
- * in the future it will require no code change.
+ * DR6_ACTIVE_LOW combines fixed-1 and active-low bits (bits that are currently
+ * fixed-1 are guaranteed to have active-low semantics if they are ever used to
+ * support a new feature).
*
- * DR6_ACTIVE_LOW is also used as the init/reset value for DR6.
+ * Note, DR6_ACTIVE_LOW is also the INIT/RESET value for DR6.
*/
#define DR6_ACTIVE_LOW 0xffff0ff0
#define DR6_VOLATILE 0x0001e80f
-#define DR6_FIXED_1 (DR6_ACTIVE_LOW & ~DR6_VOLATILE)
#define DR7_BP_EN_MASK 0x000000ff
#define DR7_GE (1 << 9)
--
2.56.0.rc1.315.gc6ed9934b7-goog
next prev parent reply other threads:[~2026-09-30 1:13 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-30 1:13 [PATCH v5 00/12] KVM: x86: Bus Lock Detect fixes and SVM support Sean Christopherson
2026-09-30 1:13 ` [PATCH v5 01/12] KVM: x86: Preserve DR6.BLD (Bus Lock Detect) when delivering #DB payload Sean Christopherson
2026-09-30 1:13 ` [PATCH v5 02/12] KVM: x86: Rename kvm_dr6_fixed() => kvm_get_dr6_fixed_1() Sean Christopherson
2026-09-30 1:13 ` [PATCH v5 03/12] KVM: Return an "unsigned long", not "u64" for the fixed-1 DR6 bits Sean Christopherson
2026-09-30 1:13 ` [PATCH v5 04/12] KVM: x86: Force fixed-1 bits in DR6 after synchronizing with hardware Sean Christopherson
2026-09-30 1:13 ` [PATCH v5 05/12] KVM: x86: WARN if fixed-1 DR6 bits aren't already set when delivering payload Sean Christopherson
2026-09-30 1:13 ` Sean Christopherson [this message]
2026-09-30 1:13 ` [PATCH v5 07/12] KVM: SVM: Add helper to query if LBR virtualization needs to be enabled Sean Christopherson
2026-09-30 1:13 ` [PATCH v5 08/12] KVM: nSVM: Disable LBRV in nested control cache when unsupported Sean Christopherson
2026-09-30 1:13 ` [PATCH v5 09/12] KVM: nSVM: Open code check on LBR virtualization being enabled in vmcb12 Sean Christopherson
2026-09-30 1:13 ` [PATCH v5 10/12] KVM: nSVM: Don't assume all active-low bits DR6 are fixed-1 Sean Christopherson
2026-09-30 1:13 ` [PATCH v5 11/12] KVM: SVM: Add a vCPU-aware helper to get supported DEBUGCTL bits Sean Christopherson
2026-09-30 1:13 ` [PATCH v5 12/12] KVM: SVM: Add support for virtualizating Bus Lock Detect Sean Christopherson
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