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

[Paolo Bonzini]

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.

>> 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.

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.
> 

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