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

Alexander Graf
2013-05-10T10:18:17Z

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;

> + 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?

> + /* 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).

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.

> + */
> +#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?

> + /* 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.

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

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
>
>