>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);
...
> 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;
The new KVM_RUN flag isn't necessary. Vendor code can directly check
switch_db_regs to decide whether to load the guest dr6 into hardware.
In svm_vcpu_run(), referencing both run_flags and switch_db_regs is confusing.
The following logic is much clearer:
if (likely(!(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT)))
svm_set_dr6(vcpu, DR6_ACTIVE_LOW);
else
svm_set_dr6(vcpu, vcpu->arch.dr6);
> } else if (unlikely(hw_breakpoint_active())) {
> set_debugreg(0, 7);
> }
>--
>2.46.0
>
>
