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Message-ID: <20130604114731.GN4725@redhat.com>
Date: Tue, 4 Jun 2013 14:47:32 +0300
From: Gleb Natapov <gleb@...hat.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
jan.kiszka@...mens.com
Subject: Re: [PATCH 1/2] KVM: x86: handle hardware breakpoints during
emulation
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@...hat.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.
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