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Message-ID: <20250815005725.2386187-3-seanjc@google.com>
Date: Thu, 14 Aug 2025 17:57:20 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: stable@...r.kernel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Sasha Levin <sashal@...nel.org>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 6.12.y 2/7] KVM: x86: Drop kvm_x86_ops.set_dr6() in favor of a
new KVM_RUN flag
[ Upstream commit 80c64c7afea1da6a93ebe88d3d29d8a60377ef80 ]
Instruct vendor code to load the guest's DR6 into hardware via a new
KVM_RUN flag, and remove kvm_x86_ops.set_dr6(), whose sole purpose was to
load vcpu->arch.dr6 into hardware when DR6 can be read/written directly
by the guest.
Note, TDX already WARNs on any run_flag being set, i.e. will yell if KVM
thinks DR6 needs to be reloaded. TDX vCPUs force KVM_DEBUGREG_AUTO_SWITCH
and never clear the flag, i.e. should never observe KVM_RUN_LOAD_GUEST_DR6.
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/r/20250610232010.162191-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
[sean: drop TDX changes]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
arch/x86/include/asm/kvm-x86-ops.h | 1 -
arch/x86/include/asm/kvm_host.h | 2 +-
arch/x86/kvm/svm/svm.c | 10 ++++++----
arch/x86/kvm/vmx/main.c | 1 -
arch/x86/kvm/vmx/vmx.c | 9 +++------
arch/x86/kvm/x86.c | 2 +-
6 files changed, 11 insertions(+), 14 deletions(-)
diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index cfb22f8c451a..861d080ed4c6 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -47,7 +47,6 @@ KVM_X86_OP(set_idt)
KVM_X86_OP(get_gdt)
KVM_X86_OP(set_gdt)
KVM_X86_OP(sync_dirty_debug_regs)
-KVM_X86_OP(set_dr6)
KVM_X86_OP(set_dr7)
KVM_X86_OP(cache_reg)
KVM_X86_OP(get_rflags)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index cccc8cbe72db..2ed05925d9d5 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1629,6 +1629,7 @@ static inline u16 kvm_lapic_irq_dest_mode(bool dest_mode_logical)
enum kvm_x86_run_flags {
KVM_RUN_FORCE_IMMEDIATE_EXIT = BIT(0),
+ KVM_RUN_LOAD_GUEST_DR6 = BIT(1),
};
struct kvm_x86_ops {
@@ -1679,7 +1680,6 @@ struct kvm_x86_ops {
void (*get_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
void (*set_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
void (*sync_dirty_debug_regs)(struct kvm_vcpu *vcpu);
- void (*set_dr6)(struct kvm_vcpu *vcpu, unsigned long value);
void (*set_dr7)(struct kvm_vcpu *vcpu, unsigned long value);
void (*cache_reg)(struct kvm_vcpu *vcpu, enum kvm_reg reg);
unsigned long (*get_rflags)(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 7d1b871cfc02..800f781475c0 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4270,10 +4270,13 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)
svm_hv_update_vp_id(svm->vmcb, vcpu);
/*
- * Run with all-zero DR6 unless needed, so that we can get the exact cause
- * of a #DB.
+ * Run with all-zero DR6 unless the guest can write DR6 freely, so that
+ * KVM can get the exact cause of a #DB. Note, loading guest DR6 from
+ * KVM's snapshot is only necessary when DR accesses won't exit.
*/
- if (likely(!(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT)))
+ if (unlikely(run_flags & KVM_RUN_LOAD_GUEST_DR6))
+ svm_set_dr6(vcpu, vcpu->arch.dr6);
+ else if (likely(!(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT)))
svm_set_dr6(vcpu, DR6_ACTIVE_LOW);
clgi();
@@ -5084,7 +5087,6 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
.set_idt = svm_set_idt,
.get_gdt = svm_get_gdt,
.set_gdt = svm_set_gdt,
- .set_dr6 = svm_set_dr6,
.set_dr7 = svm_set_dr7,
.sync_dirty_debug_regs = svm_sync_dirty_debug_regs,
.cache_reg = svm_cache_reg,
diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
index 47476fcc179a..7668e2fb8043 100644
--- a/arch/x86/kvm/vmx/main.c
+++ b/arch/x86/kvm/vmx/main.c
@@ -60,7 +60,6 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
.set_idt = vmx_set_idt,
.get_gdt = vmx_get_gdt,
.set_gdt = vmx_set_gdt,
- .set_dr6 = vmx_set_dr6,
.set_dr7 = vmx_set_dr7,
.sync_dirty_debug_regs = vmx_sync_dirty_debug_regs,
.cache_reg = vmx_cache_reg,
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 2a977cdfcd0c..b9c7940feac6 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5630,12 +5630,6 @@ void vmx_sync_dirty_debug_regs(struct kvm_vcpu *vcpu)
set_debugreg(DR6_RESERVED, 6);
}
-void vmx_set_dr6(struct kvm_vcpu *vcpu, unsigned long val)
-{
- lockdep_assert_irqs_disabled();
- set_debugreg(vcpu->arch.dr6, 6);
-}
-
void vmx_set_dr7(struct kvm_vcpu *vcpu, unsigned long val)
{
vmcs_writel(GUEST_DR7, val);
@@ -7400,6 +7394,9 @@ fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)
vmcs_writel(GUEST_RIP, vcpu->arch.regs[VCPU_REGS_RIP]);
vcpu->arch.regs_dirty = 0;
+ if (run_flags & KVM_RUN_LOAD_GUEST_DR6)
+ set_debugreg(vcpu->arch.dr6, 6);
+
/*
* Refresh vmcs.HOST_CR3 if necessary. This must be done immediately
* prior to VM-Enter, as the kernel may load a new ASID (PCID) any time
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 44ab46f2a2d2..7beea8fb6ea6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10977,7 +10977,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
set_debugreg(vcpu->arch.eff_db[3], 3);
/* When KVM_DEBUGREG_WONT_EXIT, dr6 is accessible in guest. */
if (unlikely(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT))
- kvm_x86_call(set_dr6)(vcpu, vcpu->arch.dr6);
+ run_flags |= KVM_RUN_LOAD_GUEST_DR6;
} else if (unlikely(hw_breakpoint_active())) {
set_debugreg(DR7_FIXED_1, 7);
}
--
2.51.0.rc1.163.g2494970778-goog
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