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

[Gleb Natapov <gleb@redhat.com>]

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@redhat.com>
> >> ---
> >>  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);

> 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.

> 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.