> -----Original Message-----
> From: Alexander Graf [mailto:ag...@suse.de]
> Sent: Thursday, May 02, 2013 4:35 PM
> To: Bhushan Bharat-R65777
> Cc: kvm-...@vger.kernel.org; kvm@vger.kernel.org; Wood Scott-B07421
> Subject: Re: [PATCH 7/7 v3] KVM: PPC: Add userspace debug stub support
>
>
> On 02.05.2013, at 11:46, Bhushan Bharat-R65777 wrote:
>
> >
> >
> >> -----Original Message-----
> >> From: Alexander Graf [mailto:ag...@suse.de]
> >> Sent: Friday, April 26, 2013 4:46 PM
> >> To: Bhushan Bharat-R65777
> >> Cc: kvm-...@vger.kernel.org; kvm@vger.kernel.org; Wood Scott-B07421;
> >> Bhushan
> >> Bharat-R65777
> >> Subject: Re: [PATCH 7/7 v3] KVM: PPC: Add userspace debug stub
> >> support
> >>
> >>
> >> On 08.04.2013, at 12:32, Bharat Bhushan wrote:
> >>
> >>> From: Bharat Bhushan <bharat.bhus...@freescale.com>
> >>>
> >>> This patch adds the debug stub support on booke/bookehv.
> >>> Now QEMU debug stub can use hw breakpoint, watchpoint and software
> >>> breakpoint to debug guest.
> >>>
> >>> Debug registers are saved/restored on vcpu_put()/vcpu_get().
> >>> Also the debug registers are saved restored only if guest is using
> >>> debug resources.
> >>>
> >>> Currently we do not support debug resource emulation to guest, so
> >>> always exit to user space irrespective of user space is expecting
> >>> the debug exception or not. This is unexpected event and let us
> >>> leave the action on user space. This is similar to what it was
> >>> before, only thing is that now we have proper exit state available to user
> space.
> >>>
> >>> Signed-off-by: Bharat Bhushan <bharat.bhus...@freescale.com>
> >>> ---
> >>> arch/powerpc/include/asm/kvm_host.h | 8 +
> >>> arch/powerpc/include/uapi/asm/kvm.h | 22 +++-
> >>> arch/powerpc/kvm/booke.c | 242
> >>> ++++++++++++++++++++++++++++++++-
> --
> >>> arch/powerpc/kvm/booke.h | 5 +
> >>> 4 files changed, 255 insertions(+), 22 deletions(-)
> >>>
> >>> diff --git a/arch/powerpc/include/asm/kvm_host.h
> >> b/arch/powerpc/include/asm/kvm_host.h
> >>> index e34f8fe..b9ad20f 100644
> >>> --- a/arch/powerpc/include/asm/kvm_host.h
> >>> +++ b/arch/powerpc/include/asm/kvm_host.h
> >>> @@ -505,7 +505,15 @@ struct kvm_vcpu_arch {
> >>> u32 mmucfg;
> >>> u32 epr;
> >>> u32 crit_save;
> >>> +
> >>> + /* Flag indicating that debug registers are used by guest */
> >>> + bool debug_active;
> >>> + /* for save/restore thread->dbcr0 on vcpu run/heavyweight_exit */
> >>> + u32 saved_dbcr0;
> >>> + /* guest debug registers*/
> >>> struct kvmppc_booke_debug_reg dbg_reg;
> >>> + /* shadow debug registers */
> >>> + struct kvmppc_booke_debug_reg shadow_dbg_reg;
> >>> #endif
> >>> gpa_t paddr_accessed;
> >>> gva_t vaddr_accessed;
> >>> diff --git a/arch/powerpc/include/uapi/asm/kvm.h
> >> b/arch/powerpc/include/uapi/asm/kvm.h
> >>> index c0c38ed..d7ce449 100644
> >>> --- a/arch/powerpc/include/uapi/asm/kvm.h
> >>> +++ b/arch/powerpc/include/uapi/asm/kvm.h
> >>> @@ -25,6 +25,7 @@
> >>> /* Select powerpc specific features in <linux/kvm.h> */ #define
> >>> __KVM_HAVE_SPAPR_TCE #define __KVM_HAVE_PPC_SMT
> >>> +#define __KVM_HAVE_GUEST_DEBUG
> >>>
> >>> struct kvm_regs {
> >>> __u64 pc;
> >>> @@ -267,7 +268,24 @@ struct kvm_fpu {
> >>> __u64 fpr[32];
> >>> };
> >>>
> >>> +/*
> >>> + * Defines for h/w breakpoint, watchpoint (read, write or both) and
> >>> + * software breakpoint.
> >>> + * These are used as "type" in KVM_SET_GUEST_DEBUG ioctl and "status"
> >>> + * for KVM_DEBUG_EXIT.
> >>> + */
> >>> +#define KVMPPC_DEBUG_NONE 0x0
> >>> +#define KVMPPC_DEBUG_BREAKPOINT (1UL << 1)
> >>> +#define KVMPPC_DEBUG_WATCH_WRITE (1UL << 2)
> >>> +#define KVMPPC_DEBUG_WATCH_READ (1UL << 3)
> >>> struct kvm_debug_exit_arch {
> >>> + __u64 address;
> >>> + /*
> >>> + * exiting to userspace because of h/w breakpoint, watchpoint
> >>> + * (read, write or both) and software breakpoint.
> >>> + */
> >>> + __u32 status;
> >>> + __u32 reserved;
> >>> };
> >>>
> >>> /* for KVM_SET_GUEST_DEBUG */
> >>> @@ -279,10 +297,6 @@ struct kvm_guest_debug_arch {
> >>> * Type denotes h/w breakpoint, read watchpoint, write
> >>> * watchpoint or watchpoint (both read and write).
> >>> */
> >>> -#define KVMPPC_DEBUG_NONE 0x0
> >>> -#define KVMPPC_DEBUG_BREAKPOINT (1UL << 1)
> >>> -#define KVMPPC_DEBUG_WATCH_WRITE (1UL << 2)
> >>> -#define KVMPPC_DEBUG_WATCH_READ (1UL << 3)
> >>> __u32 type;
> >>> __u32 reserved;
> >>> } bp[16];
> >>> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
> >>> index 97ae158..0e93416 100644
> >>> --- a/arch/powerpc/kvm/booke.c
> >>> +++ b/arch/powerpc/kvm/booke.c
> >>> @@ -133,6 +133,29 @@ static void kvmppc_vcpu_sync_fpu(struct
> >>> kvm_vcpu *vcpu) #endif }
> >>>
> >>> +static void kvmppc_vcpu_sync_debug(struct kvm_vcpu *vcpu) {
> >>> + /* Synchronize guest's desire to get debug interrupts into shadow
> >>> +MSR */ #ifndef CONFIG_KVM_BOOKE_HV
> >>> + vcpu->arch.shadow_msr &= ~MSR_DE;
> >>> + vcpu->arch.shadow_msr |= vcpu->arch.shared->msr & MSR_DE; #endif
> >>> +
> >>> + /* Force enable debug interrupts when user space wants to debug */
> >>> + if (vcpu->guest_debug) {
> >>> +#ifdef CONFIG_KVM_BOOKE_HV
> >>> + /*
> >>> + * Since there is no shadow MSR, sync MSR_DE into the guest
> >>> + * visible MSR.
> >>> + */
> >>> + vcpu->arch.shared->msr |= MSR_DE; #else
> >>> + vcpu->arch.shadow_msr |= MSR_DE;
> >>> + vcpu->arch.shared->msr &= ~MSR_DE; #endif
> >>> + }
> >>> +}
> >>> +
> >>> /*
> >>> * Helper function for "full" MSR writes. No need to call this if
> >>> only
> >>> * EE/CE/ME/DE/RI are changing.
> >>> @@ -150,6 +173,7 @@ void kvmppc_set_msr(struct kvm_vcpu *vcpu, u32
> >>> new_msr)
> >>> kvmppc_mmu_msr_notify(vcpu, old_msr);
> >>> kvmppc_vcpu_sync_spe(vcpu);
> >>> kvmppc_vcpu_sync_fpu(vcpu);
> >>> + kvmppc_vcpu_sync_debug(vcpu);
> >>> }
> >>>
> >>> static void kvmppc_booke_queue_irqprio(struct kvm_vcpu *vcpu, @@
> >>> -646,6 +670,46 @@ int kvmppc_core_check_requests(struct kvm_vcpu *vcpu)
> >>> return r;
> >>> }
> >>>
> >>> +static void kvmppc_load_usespace_gebug(void)
> >>
> >> ...
> >
> > Please tell What does "..." mean. Does that mean next comment is about the
> above function?
>
> It means "this one is so obvious I don't even have to write anything here".
> Usespace? Gebug? Seriously? :)
ehhh, kicking myself
>
> >
> >>
> >>> +{
> >>> + switch_booke_debug_regs(¤t->thread);
> >>> +}
> >>> +
> >>> +static void kvmppc_booke_vcpu_load_debug_regs(struct kvm_vcpu
> >>> +*vcpu) {
> >>> + if (!vcpu->arch.debug_active)
> >>> + return;
> >>> +
> >>> + /* Disable all debug events and clead pending debug events */
> >>> + mtspr(SPRN_DBCR0, 0x0);
> >>> + kvmppc_clear_dbsr();
> >>> +
> >>> + /*
> >>> + * Check whether guest still need debug resource, if not then there
> >>> + * is no need to restore guest context.
> >>> + */
> >>> + if (!vcpu->arch.shadow_dbg_reg.dbcr0)
> >>> + return;
> >>> +
> >>> + /* Load Guest Context */
> >>> + mtspr(SPRN_DBCR1, vcpu->arch.shadow_dbg_reg.dbcr1);
> >>> + mtspr(SPRN_DBCR2, vcpu->arch.shadow_dbg_reg.dbcr2); #ifdef
> >>> +CONFIG_KVM_E500MC
> >>> + mtspr(SPRN_DBCR4, vcpu->arch.shadow_dbg_reg.dbcr4);
> >>
> >> You need to make sure DBCR4 is 0 when you leave things back to normal
> >> user space. Otherwise guest debug can interfere with host debug.
> >
> >
> > ok
> >
> >>
> >>> +#endif
> >>> + mtspr(SPRN_IAC1, vcpu->arch.shadow_dbg_reg.iac[0]);
> >>> + mtspr(SPRN_IAC2, vcpu->arch.shadow_dbg_reg.iac[1]);
> >>> +#if CONFIG_PPC_ADV_DEBUG_IACS > 2
> >>> + mtspr(SPRN_IAC3, vcpu->arch.shadow_dbg_reg.iac[2]);
> >>> + mtspr(SPRN_IAC4, vcpu->arch.shadow_dbg_reg.iac[3]);
> >>> +#endif
> >>> + mtspr(SPRN_DAC1, vcpu->arch.shadow_dbg_reg.dac[0]);
> >>> + mtspr(SPRN_DAC2, vcpu->arch.shadow_dbg_reg.dac[1]);
> >>> +
> >>> + /* Enable debug events after other debug registers restored */
> >>> + mtspr(SPRN_DBCR0, vcpu->arch.shadow_dbg_reg.dbcr0); }
> >>
> >> All of the code above looks suspiciously similar to
> >> prime_debug_regs();. Can't we somehow reuse that?
> >
> > I think we can if
> > - Save thread->debug_regs in local data structure
>
> Yes, it can even be on the stack.
Thread->denug_regs is not struct , so memcpy() will not work, it is assigning
all registers one by one.
>
> > - Load vcpu->arch->debug_regs in thread->debug_regs
> > - Call prime_debug_regs();
> > - Restore thread->debug_regs from local save values in first step
>
> On heavyweight exit, based on the values on stack, yes.
>
> >
> >>
> >>> +
> >>> int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
> >>> {
> >>> int ret, s;
> >>> @@ -693,11 +757,25 @@ int kvmppc_vcpu_run(struct kvm_run *kvm_run,
> >>> struct
> >> kvm_vcpu *vcpu)
> >>> kvmppc_load_guest_fp(vcpu);
> >>> #endif
> >>>
> >>> + /*
> >>> + * Clear current->thread.dbcr0 so that kernel does not
> >>> + * restore h/w registers on context switch in vcpu running state.
> >>> + */
> >>> + vcpu->arch.debug_active = 1;
> >>
> >> = true;
> >
> > Ok
> >
> >>
> >>> + vcpu->arch.saved_dbcr0 = current->thread.dbcr0;
> >>> + current->thread.dbcr0 = 0;
> >>> + kvmppc_booke_vcpu_load_debug_regs(vcpu);
> >>
> >> static void switch_booke_debug_regs(struct thread_struct *new_thread)
> >> {
> >> if ((current->thread.dbcr0 & DBCR0_IDM)
> >> || (new_thread->dbcr0 & DBCR0_IDM))
> >> prime_debug_regs(new_thread); }
> >>
> >> The kernel will also restore debug state if the process we come from
> >> has debugging enabled. Please adjust the comment accordingly.
> >
> > kvmppc_booke_vcpu_load_debug_regs(vcpu); cleares DBSR and DBCR0, even if
> previous process have used debug registers. Is not that sufficient? I do not
> think we should load all other registers.
>
> It's sufficient, but the comment is wrong.
ok
>
> >
> >>
> >>> +
> >>> ret = __kvmppc_vcpu_run(kvm_run, vcpu);
> >>>
> >>> /* No need for kvm_guest_exit. It's done in handle_exit.
> >>> We also get here with interrupts enabled. */
> >>>
> >>> + /* Restore thread->dbcr0 */
> >>> + vcpu->arch.debug_active = 0;
> >>> + current->thread.dbcr0 = vcpu->arch.saved_dbcr0;
> >>> + kvmppc_load_usespace_gebug();
> >>> +
> >>> #ifdef CONFIG_PPC_FPU
> >>> kvmppc_save_guest_fp(vcpu);
> >>>
> >>> @@ -753,6 +831,36 @@ static int emulation_exit(struct kvm_run *run,
> >>> struct
> >> kvm_vcpu *vcpu)
> >>> }
> >>> }
> >>>
> >>> +/*
> >>> + * Currently we do not support debug resource emulation to guest,
> >>> + * so always exit to user space irrespective of user space is
> >>> + * expecting the debug exception or not. This is unexpected event
> >>> + * and let us leave the action on user space.
> >>> + */
> >>> +static int kvmppc_handle_debug(struct kvm_run *run, struct kvm_vcpu
> >>> +*vcpu) {
> >>> + u32 dbsr = mfspr(SPRN_DBSR);
> >>> +
> >>> + kvmppc_clear_dbsr();
> >>> + run->debug.arch.status = 0;
> >>> + run->debug.arch.address = vcpu->arch.pc;
> >>> +
> >>> + if (dbsr & (DBSR_IAC1 | DBSR_IAC2 | DBSR_IAC3 | DBSR_IAC4)) {
> >>> + run->debug.arch.status |= KVMPPC_DEBUG_BREAKPOINT;
> >>> + } else {
> >>> + if (dbsr & (DBSR_DAC1W | DBSR_DAC2W))
> >>> + run->debug.arch.status |= KVMPPC_DEBUG_WATCH_WRITE;
> >>> + else if (dbsr & (DBSR_DAC1R | DBSR_DAC2R))
> >>> + run->debug.arch.status |= KVMPPC_DEBUG_WATCH_READ;
> >>> + if (dbsr & (DBSR_DAC1R | DBSR_DAC1W))
> >>> + run->debug.arch.address =
> >>> vcpu->arch.shadow_dbg_reg.dac[0];
> >>> + else if (dbsr & (DBSR_DAC2R | DBSR_DAC2W))
> >>> + run->debug.arch.address =
> >>> vcpu->arch.shadow_dbg_reg.dac[1];
> >>> + }
> >>> +
> >>> + return RESUME_HOST;
> >>> +}
> >>> +
> >>> static void kvmppc_fill_pt_regs(struct pt_regs *regs) {
> >>> ulong r1, ip, msr, lr;
> >>> @@ -1112,18 +1220,10 @@ int kvmppc_handle_exit(struct kvm_run *run,
> >>> struct
> >> kvm_vcpu *vcpu,
> >>> }
> >>>
> >>> case BOOKE_INTERRUPT_DEBUG: {
> >>> - u32 dbsr;
> >>> -
> >>> - vcpu->arch.pc = mfspr(SPRN_CSRR0);
> >>> -
> >>> - /* clear IAC events in DBSR register */
> >>> - dbsr = mfspr(SPRN_DBSR);
> >>> - dbsr &= DBSR_IAC1 | DBSR_IAC2 | DBSR_IAC3 | DBSR_IAC4;
> >>> - mtspr(SPRN_DBSR, dbsr);
> >>> -
> >>> - run->exit_reason = KVM_EXIT_DEBUG;
> >>> + r = kvmppc_handle_debug(run, vcpu);
> >>> + if (r == RESUME_HOST)
> >>> + run->exit_reason = KVM_EXIT_DEBUG;
> >>> kvmppc_account_exit(vcpu, DEBUG_EXITS);
> >>> - r = RESUME_HOST;
> >>> break;
> >>> }
> >>>
> >>> @@ -1174,7 +1274,7 @@ int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
> >>> kvmppc_set_msr(vcpu, 0);
> >>>
> >>> #ifndef CONFIG_KVM_BOOKE_HV
> >>> - vcpu->arch.shadow_msr = MSR_USER | MSR_DE | MSR_IS | MSR_DS;
> >>> + vcpu->arch.shadow_msr = MSR_USER | MSR_IS | MSR_DS;
> >>> vcpu->arch.shadow_pid = 1;
> >>> vcpu->arch.shared->msr = 0;
> >>> #endif
> >>> @@ -1529,12 +1629,6 @@ int kvm_vcpu_ioctl_set_one_reg(struct
> >>> kvm_vcpu *vcpu,
> >> struct kvm_one_reg *reg)
> >>> return r;
> >>> }
> >>>
> >>> -int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
> >>> - struct kvm_guest_debug *dbg)
> >>> -{
> >>> - return -EINVAL;
> >>> -}
> >>> -
> >>> int kvm_arch_vcpu_ioctl_get_fpu(struct kvm_vcpu *vcpu, struct
> >>> kvm_fpu *fpu) {
> >>> return -ENOTSUPP;
> >>> @@ -1640,16 +1734,128 @@ void kvmppc_decrementer_func(unsigned long data)
> >>> kvmppc_set_tsr_bits(vcpu, TSR_DIS); }
> >>>
> >>> +static void kvmppc_booke_vcpu_put_debug_regs(struct kvm_vcpu *vcpu)
> >>> +{
> >>> + /* Disable all debug events First */
> >>
> >> first
> >>
> >>> + mtspr(SPRN_DBCR0, 0x0);
> >>> + /* Disable pending debug event by clearing DBSR */
> >>> + kvmppc_clear_dbsr();
> >>
> >> kvmppc_handle_debug() happens with preemption enabled, no?
> >
> > Want to clarify, preemption will be enabled on calling local_irq_enable();
> > in
> kvmppc_handle_exit()?
>
> Yes. Implicitly :).
>
> >
> >> So we can have a
> >> debug event that gets cleared on preempt by this.
> >
> > Should we read the DBSR in before local_irq_enable() in
> > kvmppc_handle_exit()?
>
> We have to, yes. Otherwise we could get preempted in between and get bogus
> data
> I presume.
Ok
Thanks
-Bharat
>
> >
> >>
> >>> +}
> >>> +
> >>> +int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
> >>> + struct kvm_guest_debug *dbg)
> >>> +{
> >>> + struct kvmppc_booke_debug_reg *dbg_reg;
> >>> + int n, b = 0, w = 0;
> >>> + const u32 bp_code[] = {
> >>> + DBCR0_IAC1 | DBCR0_IDM,
> >>> + DBCR0_IAC2 | DBCR0_IDM,
> >>> + DBCR0_IAC3 | DBCR0_IDM,
> >>> + DBCR0_IAC4 | DBCR0_IDM
> >>> + };
> >>> + const u32 wp_code[] = {
> >>> + DBCR0_DAC1W | DBCR0_IDM,
> >>> + DBCR0_DAC2W | DBCR0_IDM,
> >>> + DBCR0_DAC1R | DBCR0_IDM,
> >>> + DBCR0_DAC2R | DBCR0_IDM
> >>> + };
> >>> +
> >>> + if (!(dbg->control & KVM_GUESTDBG_ENABLE)) {
> >>> + /* Clear All debug events */
> >>> + vcpu->arch.shadow_dbg_reg.dbcr0 = 0;
> >>> + vcpu->guest_debug = 0;
> >>> +#ifdef CONFIG_KVM_BOOKE_HV
> >>> + /*
> >>> + * When user space is not using the debug resources
> >>> + * then allow guest to change the MSR.DE.
> >>> + */
> >>> + vcpu->arch.shadow_msrp &= ~MSRP_DEP; #endif
> >>> + return 0;
> >>> + }
> >>> +
> >>> +#ifdef CONFIG_KVM_BOOKE_HV
> >>> + /*
> >>> + * When user space is using the debug resource then
> >>> + * do not allow guest to change the MSR.DE.
> >>> + */
> >>> + vcpu->arch.shadow_msrp &= ~MSRP_DEP;
> >>
> >> This is supposed to be |= right?
> >
> > Yes :-)
> >
> >>
> >>> +#endif
> >>> + vcpu->guest_debug = dbg->control;
> >>> + vcpu->arch.shadow_dbg_reg.dbcr0 = 0;
> >>> + /* Set DBCR0_EDM in guest visible DBCR0 register. */
> >>> + vcpu->arch.dbg_reg.dbcr0 = DBCR0_EDM;
> >>> +
> >>> + if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
> >>> + vcpu->arch.shadow_dbg_reg.dbcr0 |= DBCR0_IDM | DBCR0_IC;
> >>> +
> >>> + if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP))
> >>> + /* Code below handles only HW breakpoints */
> >>
> >> Please move the comment out of the one-lined branch. Just put it
> >> below the return.
> >
> > Ok
> >
> >>
> >>> + return 0;
> >>> +
> >>> + dbg_reg = &(vcpu->arch.shadow_dbg_reg);
> >>> +
> >>> + /*
> >>> + * On BOOKE (e500v2); Set DBCR1 and DBCR2 to allow debug events
> >>> + * to occur when MSR.PR is set.
> >>> + * On BOOKE-HV (e500mc+); MSR.PR = 0 when guest is running. So we
> >>> + * should clear DBCR1 and DBCR2. And EPCR.DUVD is used to control
> >>> + * that debug events will not come in hypervisor (GS = 0).
> >>> + */
> >>> +#ifdef CONFIG_KVM_BOOKE_HV
> >>> + dbg_reg->dbcr1 = 0;
> >>> + dbg_reg->dbcr2 = 0;
> >>> +#else
> >>> + dbg_reg->dbcr1 = DBCR1_IAC1US | DBCR1_IAC2US | DBCR1_IAC3US |
> >>> + DBCR1_IAC4US;
> >>> + dbg_reg->dbcr2 = DBCR2_DAC1US | DBCR2_DAC2US; #endif
> >>> +
> >>> + for (n = 0; n < (KVMPPC_BOOKE_IAC_NUM + KVMPPC_BOOKE_DAC_NUM); n++) {
> >>> + u32 type = dbg->arch.bp[n].type;
> >>> +
> >>> + if (!type)
> >>> + continue;
> >>
> >> Scott's comment on why a zero-type is different from any other
> >> invalid type is still outstanding I think.
> >
> > Userspce does following
> > - dbg->arch.bp[] is first zero initialized. So dbg->arch.bp[n].type is
> > 0 (KVMPPC_DEBUG_NONE)
> > - Then set following for valid breakpoints/watchpoints:
> > -- dbg->arch.bp[n].type (KVMPPC_DEBUG_BREAKPOINT or
> > KVMPPC_DEBUG_WATCH_WRITE
> or KVMPPC_DEBUG_WATCH_READ)
> > -- dbg->arch.bp[n].addr
> >
> > I tried to avoid loop when type is 0 (probably saying type ==
> KVMPPC_DEBUG_NONE should be more clear).
>
> That works, yes.
>
> > if type is invalid then should we return -EINVAL.
>
> Yes.
>
>
> Alex
>
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