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

[Gleb Natapov]

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?

>  	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();

>  };
>  
>  #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.
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