Re: [PATCH 2/3] KVM: x86: handle hardware breakpoints during emulation

Gleb Natapov
2013-07-31T10:00:41Z

On Tue, Jul 30, 2013 at 05:11:35PM +0200, Paolo Bonzini wrote:
> This lets debugging work better during emulation of invalid
> guest state.
>
> The check is done before emulating the instruction, and (in the case
> of guest debugging) reuses EMULATE_DO_MMIO to exit with KVM_EXIT_DEBUG.
>
Not EMULATE_DO_MMIO any more. Otherwise looks good.

> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> arch/x86/kvm/x86.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 66 insertions(+)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c2a0674..1368cf5 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4956,6 +4956,62 @@ static bool retry_instruction(struct x86_emulate_ctxt *ctxt,
> static int complete_emulated_mmio(struct kvm_vcpu *vcpu);
> static int complete_emulated_pio(struct kvm_vcpu *vcpu);
>
> +static int kvm_vcpu_check_hw_bp(unsigned long addr, u32 type, u32 dr7,
> + unsigned long *db)
> +{
> + u32 dr6 = 0;
> + int i;
> + u32 enable, rwlen;
> +
> + enable = dr7;
> + rwlen = dr7 >> 16;
> + for (i = 0; i < 4; i++, enable >>= 2, rwlen >>= 4)
> + if ((enable & 3) && (rwlen & 15) == type && db[i] == addr)
> + dr6 |= (1 << i);
> + return dr6;
> +}
> +
> +static bool kvm_vcpu_check_breakpoint(struct kvm_vcpu *vcpu, int *r)
> +{
> + struct kvm_run *kvm_run = vcpu->run;
> + unsigned long eip = vcpu->arch.emulate_ctxt.eip;
> + u32 dr6 = 0;
> +
> + if (unlikely(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) &&
> + (vcpu->arch.guest_debug_dr7 & DR7_BP_EN_MASK)) {
> + dr6 = kvm_vcpu_check_hw_bp(eip, 0,
> + vcpu->arch.guest_debug_dr7,
> + vcpu->arch.eff_db);
> +
> + if (dr6 != 0) {
> + kvm_run->debug.arch.dr6 = dr6 | DR6_FIXED_1;
> + kvm_run->debug.arch.pc = kvm_rip_read(vcpu) +
> + get_segment_base(vcpu, VCPU_SREG_CS);
> +
> + kvm_run->debug.arch.exception = DB_VECTOR;
> + kvm_run->exit_reason = KVM_EXIT_DEBUG;
> + *r = EMULATE_USER_EXIT;
> + return true;
> + }
> + }
> +
> + if (unlikely(vcpu->arch.dr7 & DR7_BP_EN_MASK)) {
> + dr6 = kvm_vcpu_check_hw_bp(eip, 0,
> + vcpu->arch.dr7,
> + vcpu->arch.db);
> +
> + if (dr6 != 0) {
> + vcpu->arch.dr6 &= ~15;
> + vcpu->arch.dr6 |= dr6;
> + kvm_queue_exception(vcpu, DB_VECTOR);
> + *r = EMULATE_DONE;
> + return true;
> + }
> + }
> +
> + return false;
> +}
> +
> int x86_emulate_instruction(struct kvm_vcpu *vcpu,
> unsigned long cr2,
> int emulation_type,
> @@ -4976,6 +5032,16 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
>
> if (!(emulation_type & EMULTYPE_NO_DECODE)) {
> init_emulate_ctxt(vcpu);
> +
> + /*
> + * We will reenter on the same instruction since
> + * we do not set complete_userspace_io. This does not
> + * handle watchpoints yet, those would be handled in
> + * the emulate_ops.
> + */
> + if (kvm_vcpu_check_breakpoint(vcpu, &r))
> + return r;
> +
> ctxt->interruptibility = 0;
> ctxt->have_exception = false;
> ctxt->perm_ok = false;
> --
> 1.8.1.4
>

--
Gleb.