RE: [PATCH] KVM: PPC: Add userspace debug stub support

Bhushan Bharat-R65777
2013-05-10T17:31:46Z

> -----Original Message-----
> From: Alexander Graf [mailto:agraf@suse.de]
> Sent: Friday, May 10, 2013 3:48 PM
> To: Bhushan Bharat-R65777
> Cc: kvm-ppc@vger.kernel.org; kvm@vger.kernel.org; Wood Scott-B07421;
> tiejun.chen@windriver.com; Bhushan Bharat-R65777
> Subject: Re: [PATCH] KVM: PPC: Add userspace debug stub support
>
>
> On 07.05.2013, at 11:40, Bharat Bhushan wrote:
>
> > 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.
> >
> > This is how we save/restore debug register context when switching
> > between guest, userspace and kernel user-process:
> >
> > When QEMU is running
> > -> thread->debug_reg = QEMU debug register context.
> > -> Kernel will handle switching the debug register on context switch.
> > -> no vcpu_load() called
> >
> > QEMU makes ioctls (except RUN)
> > -> This will call vcpu_load()
> > -> should not change context.
> > -> Some ioctls can change vcpu debug register, context saved in
> > -> vcpu->debug_regs
> >
> > QEMU Makes RUN ioctl
> > -> Save thread->debug_reg on STACK
> > -> Store thread->debug_reg = vcpu->debug_reg load thread->debug_reg
> > -> RUN VCPU ( So thread points to vcpu context )
> >
> > Context switch happens When VCPU running
> > -> makes vcpu_load() should not load any context kernel loads the vcpu
> > -> context as thread->debug_regs points to vcpu context.
> >
> > On heavyweight_exit
> > -> Load the context saved on stack in thread->debug_reg
> >
> > Currently we do not support debug resource emulation to guest, On
> > debug exception, always exit to user space irrespective of user space
> > is expecting the debug exception or not. If this is unexpected
> > exception (breakpoint/watchpoint event not set by
> > userspace) then 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.bhushan@freescale.com>
> > ---
> > arch/powerpc/include/asm/kvm_host.h | 3 +
> > arch/powerpc/include/uapi/asm/kvm.h | 1 +
> > arch/powerpc/kvm/booke.c | 242 ++++++++++++++++++++++++++++++++---
> > arch/powerpc/kvm/booke.h | 5 +
> > 4 files changed, 233 insertions(+), 18 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/kvm_host.h
> > b/arch/powerpc/include/asm/kvm_host.h
> > index 838a577..1b29945 100644
> > --- a/arch/powerpc/include/asm/kvm_host.h
> > +++ b/arch/powerpc/include/asm/kvm_host.h
> > @@ -524,7 +524,10 @@ struct kvm_vcpu_arch {
> > u32 eptcfg;
> > u32 epr;
> > u32 crit_save;
> > + /* guest debug registers*/
> > struct debug_reg dbg_reg;
> > + /* shadow debug registers */
>
> Please be more verbose here. What exactly does this contain? Why do we need
> shadow and non-shadow registers? The comment as it is reads like
>
> /* Add one plus one */
> x = 1 + 1;

/*
* Shadow debug registers hold the debug register content
* to be written in h/w debug register on behalf of guest
* written value or user space written value.
*/

>
> > + struct 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 ded0607..f5077c2 100644
> > --- a/arch/powerpc/include/uapi/asm/kvm.h
> > +++ b/arch/powerpc/include/uapi/asm/kvm.h
> > @@ -27,6 +27,7 @@
> > #define __KVM_HAVE_PPC_SMT
> > #define __KVM_HAVE_IRQCHIP
> > #define __KVM_HAVE_IRQ_LINE
> > +#define __KVM_HAVE_GUEST_DEBUG
> >
> > struct kvm_regs {
> > __u64 pc;
> > diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c index
> > ef99536..6a44ad4 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, @@
> > -655,6 +679,7 @@ int kvmppc_core_check_requests(struct kvm_vcpu *vcpu)
> > int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu) {
> > int ret, s;
> > + struct debug_reg debug;
> > #ifdef CONFIG_PPC_FPU
> > unsigned int fpscr;
> > int fpexc_mode;
> > @@ -699,11 +724,27 @@ 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.
> > + */
>
> Incorrect comment?

Leftover from previous code, will remove this.

>
> > + /* Save thread->debug context on stack */
>
> /* Switch to guest debug context */
>
> > + memcpy(&debug, &current->thread.debug, sizeof(struct debug_reg));
>
> debug = current->thread.debug;
>
> > + /* Load vcpu debug context in thread->debug */
> > + memcpy(&current->thread.debug, &vcpu->arch.shadow_dbg_reg,
> > + sizeof(struct debug_reg));
>
> current->thread.debug = vcpu->arch.shadow_dbg_reg;
>
> > +
> > + switch_booke_debug_regs(&current->thread);
> > +
> > 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 userspace context in thread->dbcr0 from stack*/
>
> /* Switch back to user space debug context */
>
> > + memcpy(&current->thread.debug, &debug, sizeof(struct debug_reg));
>
> current->thread.debug = debug;
>
> > + switch_booke_debug_regs(&current->thread);
> > +
> > #ifdef CONFIG_PPC_FPU
> > kvmppc_save_guest_fp(vcpu);
> >
> > @@ -759,6 +800,36 @@ 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.
>
> Please rework your wording.
>
> > + */
> > +static int kvmppc_handle_debug(struct kvm_run *run, struct kvm_vcpu
> > +*vcpu) {
> > + struct debug_reg *dbg_reg = &(vcpu->arch.shadow_dbg_reg);
> > + u32 dbsr = vcpu->arch.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 = dbg_reg->dac1;
> > + else if (dbsr & (DBSR_DAC2R | DBSR_DAC2W))
> > + run->debug.arch.address = dbg_reg->dac2;
> > + }
> > +
> > + return RESUME_HOST;
> > +}
> > +
> > static void kvmppc_fill_pt_regs(struct pt_regs *regs) {
> > ulong r1, ip, msr, lr;
> > @@ -819,6 +890,11 @@ static void kvmppc_restart_interrupt(struct kvm_vcpu
> *vcpu,
> > case BOOKE_INTERRUPT_CRITICAL:
> > unknown_exception(&regs);
> > break;
> > + case BOOKE_INTERRUPT_DEBUG:
> > + /* Save DBSR before preemption is enabled */
> > + vcpu->arch.dbsr = mfspr(SPRN_DBSR);
> > + kvmppc_clear_dbsr();
> > + break;
> > }
> > }
> >
> > @@ -1118,18 +1194,10 @@ 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;
> > }
> >
> > @@ -1180,7 +1248,7 @@ 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
> > @@ -1557,12 +1625,6 @@ 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;
> > @@ -1668,6 +1730,145 @@ void kvmppc_decrementer_func(unsigned long data)
> > kvmppc_set_tsr_bits(vcpu, TSR_DIS);
> > }
> >
> > +static int kvmppc_booke_set_breakpoint(struct kvm_vcpu *vcpu,
> > +uint64_t addr,
>
> s/set/add/
>
> > + int index)
> > +{
> > + struct debug_reg *dbg_reg = &(vcpu->arch.shadow_dbg_reg);
> > +
> > + switch (index) {
> > + case 0:
> > + dbg_reg->dbcr0 |= DBCR0_IAC1 | DBCR0_IDM;
> > + dbg_reg->iac1 = addr;
> > + break;
> > + case 1:
> > + dbg_reg->dbcr0 |= DBCR0_IAC2 | DBCR0_IDM;
> > + dbg_reg->iac2 = addr;
> > + break;
> > +#if CONFIG_PPC_ADV_DEBUG_IACS > 2
> > + case 2:
> > + dbg_reg->dbcr0 |= DBCR0_IAC3 | DBCR0_IDM;
> > + dbg_reg->iac3 = addr;
> > + break;
> > + case 3:
> > + dbg_reg->dbcr0 |= DBCR0_IAC4 | DBCR0_IDM;
> > + dbg_reg->iac4 = addr;
> > + break;
> > +#endif
> > + default:
> > + return -EINVAL;
> > + }
>
> dbg_reg->dbcr0 |= DBCR0_IDM;
>
> > + return 0;
> > +}
> > +
> > +static int kvmppc_booke_set_watchpoint(struct kvm_vcpu *vcpu,
> > +uint64_t addr,
>
> s/set/add/
>
> > + int type, int index)
> > +{
> > + struct debug_reg *dbg_reg = &(vcpu->arch.shadow_dbg_reg);
> > +
> > + switch (index) {
> > + case 0:
> > + if (type & KVMPPC_DEBUG_WATCH_READ)
> > + dbg_reg->dbcr0 |= DBCR0_DAC1R | DBCR0_IDM;
> > + if (type & KVMPPC_DEBUG_WATCH_WRITE)
> > + dbg_reg->dbcr0 |= DBCR0_DAC1W | DBCR0_IDM;
> > + dbg_reg->dac1 = addr;
> > + break;
> > + case 1:
> > + if (type & KVMPPC_DEBUG_WATCH_READ)
> > + dbg_reg->dbcr0 |= DBCR0_DAC2R | DBCR0_IDM;
> > + if (type & KVMPPC_DEBUG_WATCH_WRITE)
> > + dbg_reg->dbcr0 |= DBCR0_DAC2W | DBCR0_IDM;
> > + dbg_reg->dac2 = addr;
> > + break;
> > + default:
> > + return -EINVAL;
> > + }
>
> dbg_reg->dbcr0 |= DBCR0_IDM;
>
> > + return 0;
> > +}
> > +
> > +int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
> > + struct kvm_guest_debug *dbg)
> > +{
> > + struct debug_reg *dbg_reg;
> > + int n, b = 0, w = 0;
> > +
> > + 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
>
> guest_may_set_msr_de(vcpu, true);
>
> > + 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;
> > +#endif
>
> guest_may_set_msr_de(vcpu, false);
>
> > + 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))
> > + return 0;
> > +
> > + /* Code below handles only HW breakpoints */
> > + 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).

Will rework the above comment as discussed.

>
> This is still wrong. We want to trap in PR=1. It's what PR KVM does, it's what
> TCG does. There is no point in making HV KVM behave differently.

This comment is not valid.

>
> > + */
> > +#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++) {
> > + uint64_t addr = dbg->arch.bp[n].addr;
> > + uint32_t type = dbg->arch.bp[n].type;
> > +
> > + if (type = KVMPPC_DEBUG_NONE)
> > + continue;
> > +
> > + if (type & !(KVMPPC_DEBUG_WATCH_READ |
> > + KVMPPC_DEBUG_WATCH_WRITE |
> > + KVMPPC_DEBUG_BREAKPOINT))
> > + return -EINVAL;
> > +
> > + if (type & KVMPPC_DEBUG_BREAKPOINT) {
> > + /* Setting H/W breakpoint */
> > + if (kvmppc_booke_set_breakpoint(vcpu, addr, b++))
>
> Please pass dbg_reg into the function
>
> > + return -EINVAL;
> > + } else {
> > + /* Setting H/W watchpoint */
> > + if (kvmppc_booke_set_watchpoint(vcpu, addr, type, w++))
>
> here too
>
> > + return -EINVAL;
> > + }
> > + }
> > +
> > + return 0;
> > +}
> > +
> > void kvmppc_booke_vcpu_load(struct kvm_vcpu *vcpu, int cpu) {
> > vcpu->cpu = smp_processor_id();
> > @@ -1678,6 +1879,11 @@ void kvmppc_booke_vcpu_put(struct kvm_vcpu
> > *vcpu) {
> > current->thread.kvm_vcpu = NULL;
> > vcpu->cpu = -1;
> > +
> > + /* Disable all debug events */
> > + mtspr(SPRN_DBCR0, 0x0);
>
> Why? Wouldn't normal preemption handling take care of this already?

Yes, normal preemption will take care. On vcpu_put we do not clear EPCR.DUVD and DBCR1/2.
So debug event will not be taken in host.

So yes, it is not needed here.

>
> > + /* Clear pending debug event in DBSR */
> > + kvmppc_clear_dbsr();
>
> Is there a chance we will ever have to do this? On debug exits from guest
> context we already clear dbsr.

DBSR can have events captured but not delivered as interrupt if MSR.DE is clear. I know with qemu debug stub we do not allow msr.de to be cleared by guest.

>
> My question from the last review round still stands. What if a breakpoint for
> guest address 0xc0001234 is active and on the host 0xc0001234 happens to be at
> kvm_run? Will we get a breakpoint inside of the host context? That would be bad.
> We only want to get debug events when
>
> e500v2: MSR.PR = 1
> e500mc: MSR.GS = 1

I responded last time also when you asked this question. Here I am pasting same answer again:
"No,
On e500v2, we uses DBCR1 and DBCR2 to not allow debug events when MSR.PR = 0 On e500mc+, we uses EPCR.DUVD to not allow debug events when in hypervisor mode.
"

This answer to your question as we discussed on IRC.

-Bharat

>
>
> Alex
>
> > }
> >
> > int __init kvmppc_booke_init(void)
> > diff --git a/arch/powerpc/kvm/booke.h b/arch/powerpc/kvm/booke.h index
> > 5fd1ba6..a1ff67d 100644
> > --- a/arch/powerpc/kvm/booke.h
> > +++ b/arch/powerpc/kvm/booke.h
> > @@ -129,4 +129,9 @@ static inline void kvmppc_save_guest_fp(struct kvm_vcpu
> *vcpu)
> > giveup_fpu(current);
> > #endif
> > }
> > +
> > +static inline void kvmppc_clear_dbsr(void) {
> > + mtspr(SPRN_DBSR, mfspr(SPRN_DBSR));
> > +}
> > #endif /* __KVM_BOOKE_H__ */
> > --
> > 1.5.6.5
> >
> >
>