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KVM: x86: Drop kvm_x86_ops.set_dr6() in favor of a new KVM_RUN flag

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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@vger.kernel.org
Link: https://lore.kernel.org/r/20250610232010.162191-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2025-06-10 16:20:05 -07:00
parent 2478b1b220
commit 80c64c7afe
6 changed files with 11 additions and 22 deletions
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1
arch/x86/include/asm/kvm-x86-ops.h
View File

@ -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)

2
arch/x86/include/asm/kvm_host.h
View File

@ -1676,6 +1676,7 @@ 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 {
@ -1728,7 +1729,6 @@ 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);

10
arch/x86/kvm/svm/svm.c
View File

@ -4438,10 +4438,13 @@ 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();
@ -5252,7 +5255,6 @@ 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,

9
arch/x86/kvm/vmx/main.c
View File

@ -489,14 +489,6 @@ 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))
@ -943,7 +935,6 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
.set_idt = vt_op(set_idt),
.get_gdt = vt_op(get_gdt),
.set_gdt = vt_op(set_gdt),
.set_dr6 = vt_op(set_dr6),
.set_dr7 = vt_op(set_dr7),
.sync_dirty_debug_regs = vt_op(sync_dirty_debug_regs),
.cache_reg = vt_op(cache_reg),

9
arch/x86/kvm/vmx/vmx.c
View File

@ -5606,12 +5606,6 @@ 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);
@ -7370,6 +7364,9 @@ 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

2
arch/x86/kvm/x86.c
View File

@ -11046,7 +11046,7 @@ 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);
}