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Message-ID: <20250515005353.952707-3-mlevitsk@redhat.com>
Date: Wed, 14 May 2025 20:53:51 -0400
From: Maxim Levitsky <mlevitsk@...hat.com>
To: kvm@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
Sean Christopherson <seanjc@...gle.com>,
Borislav Petkov <bp@...en8.de>,
x86@...nel.org,
Ingo Molnar <mingo@...hat.com>,
linux-kernel@...r.kernel.org,
"H. Peter Anvin" <hpa@...or.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH v4 2/4] KVM: x86: Drop kvm_x86_ops.set_dr6() in favor of a new KVM_RUN flag
From: Sean Christopherson <seanjc@...gle.com>
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.
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 | 9 ---------
arch/x86/kvm/vmx/vmx.c | 9 +++------
arch/x86/kvm/x86.c | 2 +-
6 files changed, 11 insertions(+), 22 deletions(-)
diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index 79406bf07a1c..a2248817470c 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -49,7 +49,6 @@ 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 c04f73cf062f..d2ad31a1628e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1672,6 +1672,7 @@ 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 {
@@ -1724,7 +1725,6 @@ 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 c8b8a9947057..026b28051fff 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4308,10 +4308,13 @@ 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();
@@ -5119,7 +5122,6 @@ 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 a8e80d66e77a..28f854055e2c 100644
--- a/arch/x86/kvm/vmx/main.c
+++ b/arch/x86/kvm/vmx/main.c
@@ -498,14 +498,6 @@ static void vt_set_gdt(struct kvm_vcpu *vcpu, struct desc_ptr *dt)
vmx_set_gdt(vcpu, dt);
}
-static void vt_set_dr6(struct kvm_vcpu *vcpu, unsigned long val)
-{
- if (is_td_vcpu(vcpu))
- return;
-
- vmx_set_dr6(vcpu, val);
-}
-
static void vt_set_dr7(struct kvm_vcpu *vcpu, unsigned long val)
{
if (is_td_vcpu(vcpu))
@@ -945,7 +937,6 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
.set_idt = vt_set_idt,
.get_gdt = vt_get_gdt,
.set_gdt = vt_set_gdt,
- .set_dr6 = vt_set_dr6,
.set_dr7 = vt_set_dr7,
.sync_dirty_debug_regs = vt_sync_dirty_debug_regs,
.cache_reg = vt_cache_reg,
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 609563da270c..9953de0cb32a 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5611,12 +5611,6 @@ 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);
@@ -7371,6 +7365,9 @@ 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 25de78cdab42..684b8047e0f2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11019,7 +11019,7 @@ 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(0, 7);
}
--
2.46.0
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