On 2013-12-31 16:28, Paolo Bonzini wrote: > Il 27/12/2013 19:17, Jan Kiszka ha scritto: >> >> From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> >> >> In contrast to VMX, SVM dose not automatically transfer DR6 into the >> VCPU's arch.dr6. So if we face a DR6 read, we must consult a new vendor >> hook to obtain the current value. And as SVM now picks the DR6 state >> from its VMCB, we also need a set callback in order to write updates of >> DR6 back. >> >> Fixes a regression of 020df0794f. >> >> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> >> --- >> arch/x86/include/asm/kvm_host.h | 2 ++ >> arch/x86/kvm/svm.c | 18 ++++++++++++++++++ >> arch/x86/kvm/vmx.c | 11 +++++++++++ >> arch/x86/kvm/x86.c | 3 ++- >> 4 files changed, 33 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h >> index ae5d783..e73651b 100644 >> --- a/arch/x86/include/asm/kvm_host.h >> +++ b/arch/x86/include/asm/kvm_host.h >> @@ -699,6 +699,8 @@ struct kvm_x86_ops { >> void (*set_idt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt); >> void (*get_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt); >> void (*set_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt); >> + u64 (*get_dr6)(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.c b/arch/x86/kvm/svm.c >> index c7168a5..5987414 100644 >> --- a/arch/x86/kvm/svm.c >> +++ b/arch/x86/kvm/svm.c >> @@ -1671,6 +1671,22 @@ static void new_asid(struct vcpu_svm *svm, struct svm_cpu_data *sd) >> mark_dirty(svm->vmcb, VMCB_ASID); >> } >> >> +static u64 svm_get_dr6(struct kvm_vcpu *vcpu) >> +{ >> + if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) >> + return vcpu->arch.dr6; >> + else >> + return to_svm(vcpu)->vmcb->save.dr6; >> +} >> + >> +static void svm_set_dr6(struct kvm_vcpu *vcpu, unsigned long value) >> +{ >> + struct vcpu_svm *svm = to_svm(vcpu); >> + >> + svm->vmcb->save.dr6 = value; >> + mark_dirty(svm->vmcb, VMCB_DR); > > The code here is a bit different from the existing DR7 hooks. Why isn't > get_dr7 needed? I cannot find anything in the AMD manuals that suggests > a difference between DR6 and DR7. DR7 doesn't change while the guest is running, only when the guest writes to it, and we intercept that. > > Also, set_dr7 is only called when !(vcpu->guest_debug & > KVM_GUESTDBG_USE_HW_BP). I think it makes sense to do the same for all > the new hooks you need to introduce (get_dr6, set_dr6 and possibly get_dr7). We could make set_dr6 conditional, but it doesn't make a difference in practice. If guest debugging is enabled, we effectively only use DR6 when leaving the guest, i.e. when the hardware defined DR6. Hmm, SVM is not updating kvm_run::debug.arch.dr6/7... There might be more broken, need to check. But that would not be guest visible then. > > And finally, is it necessary to write to both vcpu->arch.dr6/7 and > svm->vmcb->save.dr6/7, or is it simply okay to do that? arch.dr6/7 holds the guest visible state, save.dr6/7 the effective one. Jan PS: I'll look into a kvm unit test for hardware debugging features these days. Guest-side at least, no idea yet how to implement host-side debugging with unit tests.
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