Re: [PATCH 1/2] KVM: x86: handle hardware breakpoints duringemulation

From: Gleb Natapov
Date: Tue Jun 04 2013 - 08:53:22 EST

On Tue, Jun 04, 2013 at 02:19:13PM +0200, Paolo Bonzini wrote:
> Il 04/06/2013 13:47, Gleb Natapov ha scritto:
> > On Tue, Jun 04, 2013 at 01:33:20PM +0200, Paolo Bonzini wrote:
> >> Il 04/06/2013 13:28, Gleb Natapov ha scritto:
> >>> On Thu, May 30, 2013 at 06:00:30PM +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.
> >>>>
> >>>> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> >>>> ---
> >>>> arch/x86/include/asm/kvm_host.h | 3 +-
> >>>> arch/x86/kvm/x86.c | 65 +++++++++++++++++++++++++++++++++++++++++
> >>>> 2 files changed, 67 insertions(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> >>>> index e2e09f3..aefd8c2 100644
> >>>> --- a/arch/x86/include/asm/kvm_host.h
> >>>> +++ b/arch/x86/include/asm/kvm_host.h
> >>>> @@ -788,9 +788,10 @@ extern u32 kvm_min_guest_tsc_khz;
> >>>> extern u32 kvm_max_guest_tsc_khz;
> >>>>
> >>>> enum emulation_result {
> >>>> - EMULATE_DONE, /* no further processing */
> >>>> - EMULATE_DO_MMIO, /* kvm_run filled with mmio request */
> >>>> + EMULATE_DONE, /* no further processing */
> >>>> + EMULATE_DO_MMIO, /* kvm_run ready for userspace exit */
> >>> If it no longer means MMIO (or PIO) lest rename it to something more
> >>> meaningful. EMULATE_EXIT? EMULATE_USER_EXIT?
> >>
> >> I'll go with EMULATE_USER_EXIT.
> >>
> >>>> EMULATE_FAIL, /* can't emulate this instruction */
> >>>> + EMULATE_PROCEED, /* proceed with rest of emulation */
> >>> I think we can do without this. Have to function: check_bp(),
> >>> handle_bp(). Do:
> >>>
> >>> if (check_bp())
> >>> return handle_bp();
> >>
> >> I tried this, but it doesn't work because you need to pass the computed
> >> dr6 from check_bp to handle_bp. It becomes really ugly.
> >>
> > Can't check_bp() return dr6?
> >
> > if ((dr6 = check_bp())
> > return handle_bp(dr6);
>
> It also needs to know if debugging the guest vs. in the guest. Thus
> there is duplicate code between check and handle.
>
Yeah. What about:
if ((dr6 = guest_debug()))
return handle_gues_debug();
else if ((dr6 = check_bp()))
return handle_bp(dr6);

> >> If you do not want EMULATE_PROCEED, I can just use -1 instead in
> >> kvm_vcpu_check_breakpoint, and return if r < 0.
> >>
> > But you need to know what to return EMULATE_DONE or EMULATE_USER_EXIT.
>
> Sorry, _not_ return if r < 0.
>
Function that returns enum or -1? This is worse IMO. Return
EMULATE_DONE/EMULATE_USER_EXIT via a pointer will be better.

> Paolo
>
> >> Paolo
> >>
> >>>> };
> >>>>
> >>>> #define EMULTYPE_NO_DECODE (1 << 0)
> >>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >>>> index 1d928af..33b51bc 100644
> >>>> --- a/arch/x86/kvm/x86.c
> >>>> +++ b/arch/x86/kvm/x86.c
> >>>> @@ -4872,6 +4872,60 @@ 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 int kvm_vcpu_check_breakpoint(struct kvm_vcpu *vcpu)
> >>>> +{
> >>>> + 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;
> >>>> + return EMULATE_DO_MMIO;
> >>>> + }
> >>>> + }
> >>>> +
> >>>> + 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);
> >>>> + return EMULATE_DONE;
> >>>> + }
> >>>> + }
> >>>> +
> >>>> + return EMULATE_PROCEED;
> >>>> +}
> >>>> +
> >>>> int x86_emulate_instruction(struct kvm_vcpu *vcpu,
> >>>> unsigned long cr2,
> >>>> int emulation_type,
> >>>> @@ -4892,6 +4946,17 @@ 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.
> >>>> + */
> >>>> + r = kvm_vcpu_check_breakpoint(vcpu);
> >>>> + if (r != EMULATE_PROCEED)
> >>>> + return r;
> >>>> +
> >>>> ctxt->interruptibility = 0;
> >>>> ctxt->have_exception = false;
> >>>> ctxt->perm_ok = false;
> >>>> --
> >>>> 1.8.1.4
> >>>>
> >>>
> >>> --
> >>> Gleb.
> >>>
> >
> > --
> > Gleb.
> >

--
Gleb.
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