On Tue, Nov 25, 2014 at 04:10:03PM +0000, Alex Bennée wrote:
> This adds support for single-stepping the guest. As userspace can and
> will manipulate guest registers before restarting any tweaking of the
> registers has to occur just before control is passed back to the guest.
> Furthermore while guest debugging is in effect we need to squash the
> ability of the guest to single-step itself as we have no easy way of
> re-entering the guest after the exception has been delivered to the
> hypervisor.
>
> Signed-off-by: Alex Bennée <alex.ben...@linaro.org>
>
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index 48d26bb..a76daae 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -38,6 +38,7 @@
> #include <asm/tlbflush.h>
> #include <asm/cacheflush.h>
> #include <asm/virt.h>
> +#include <asm/debug-monitors.h>
> #include <asm/kvm_arm.h>
> #include <asm/kvm_asm.h>
> #include <asm/kvm_mmu.h>
> @@ -300,6 +301,17 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
> kvm_arm_set_running_vcpu(NULL);
> }
>
> +/**
> + * kvm_arch_vcpu_ioctl_set_guest_debug - Setup guest debugging
> + * @kvm: pointer to the KVM struct
> + * @kvm_guest_debug: the ioctl data buffer
> + *
> + * This sets up the VM for guest debugging. Care has to be taken when
> + * manipulating guest registers as these will be set/cleared by the
> + * hyper-visor controller, typically before each kvm_run event. As a
> + * result modification of the guest registers needs to take place
> + * after they have been restored in the hyp.S trampoline code.
> + */
> int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
> struct kvm_guest_debug *dbg)
> {
> @@ -317,8 +329,8 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu
> *vcpu,
>
> /* Single Step */
> if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
> - kvm_info("SS requested, not yet implemented\n");
> - return -EINVAL;
> + kvm_info("SS requested\n");
> + route_el2 = true;
> }
>
> /* Software Break Points */
> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> index 8da1043..78e5ae1 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -121,6 +121,7 @@ int main(void)
> DEFINE(VCPU_FAR_EL2, offsetof(struct kvm_vcpu,
> arch.fault.far_el2));
> DEFINE(VCPU_HPFAR_EL2, offsetof(struct kvm_vcpu,
> arch.fault.hpfar_el2));
> DEFINE(VCPU_DEBUG_FLAGS, offsetof(struct kvm_vcpu, arch.debug_flags));
> + DEFINE(GUEST_DEBUG, offsetof(struct kvm_vcpu, guest_debug));
> DEFINE(VCPU_HCR_EL2, offsetof(struct kvm_vcpu,
> arch.hcr_el2));
> DEFINE(VCPU_MDCR_EL2, offsetof(struct kvm_vcpu, arch.mdcr_el2));
> DEFINE(VCPU_IRQ_LINES, offsetof(struct kvm_vcpu, arch.irq_lines));
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 28dc92b..6def054 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -91,6 +91,25 @@ static int kvm_handle_bkpt(struct kvm_vcpu *vcpu, struct
> kvm_run *run)
> return 0;
> }
>
> +/**
> + * kvm_handle_ss - handle single step exceptions
> + *
> + * @vcpu: the vcpu pointer
same @run comment as other handler header in previous patch
> + *
> + * See: ARM ARM D2.12 for the details. While the host is routing debug
> + * exceptions to it's handlers we have to suppress the ability of the
> + * guest to trigger exceptions.
> + */
> +static int kvm_handle_ss(struct kvm_vcpu *vcpu, struct kvm_run *run)
> +{
> + WARN_ON(!(vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP));
I'm not sure about this WARN_ON. Is there some scenario you were
thinking of when you put it here? Is there some scenario where this
could trigger so frequently we kill the log buffer?
> +
> + run->exit_reason = KVM_EXIT_DEBUG;
> + run->debug.arch.exit_type = KVM_DEBUG_EXIT_SINGLE_STEP;
> + run->debug.arch.address = *vcpu_pc(vcpu);
> + return 0;
> +}
> +
> static exit_handle_fn arm_exit_handlers[] = {
> [ESR_EL2_EC_WFI] = kvm_handle_wfx,
> [ESR_EL2_EC_CP15_32] = kvm_handle_cp15_32,
> @@ -105,6 +124,7 @@ static exit_handle_fn arm_exit_handlers[] = {
> [ESR_EL2_EC_SYS64] = kvm_handle_sys_reg,
> [ESR_EL2_EC_IABT] = kvm_handle_guest_abort,
> [ESR_EL2_EC_DABT] = kvm_handle_guest_abort,
> + [ESR_EL2_EC_SOFTSTP] = kvm_handle_ss,
> [ESR_EL2_EC_BKPT32] = kvm_handle_bkpt,
> [ESR_EL2_EC_BRK64] = kvm_handle_bkpt,
> };
> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
> index 3c733ea..c0bc218 100644
> --- a/arch/arm64/kvm/hyp.S
> +++ b/arch/arm64/kvm/hyp.S
> @@ -16,6 +16,7 @@
> */
>
> #include <linux/linkage.h>
> +#include <linux/kvm.h>
>
> #include <asm/assembler.h>
> #include <asm/memory.h>
> @@ -168,6 +169,31 @@
> // x19-x29, lr, sp*, elr*, spsr*
> restore_common_regs
>
> + // After restoring the guest registers but before we return to the guest
> + // we may want to make some final tweaks to support guest debugging.
> + ldr x3, [x0, #GUEST_DEBUG]
> + tbz x3, #KVM_GUESTDBG_ENABLE_SHIFT, 2f // No guest debug
> +
> + // x0 - preserved as VCPU ptr
> + // x1 - spsr
> + // x2 - mdscr
> + mrs x1, spsr_el2
> + mrs x2, mdscr_el1
> +
> + // See ARM ARM D2.12.3 The software step state machine
> + // If we are doing Single Step - set MDSCR_EL1.SS and PSTATE.SS
> + orr x1, x1, #DBG_SPSR_SS
> + orr x2, x2, #DBG_MDSCR_SS
> + tbnz x3, #KVM_GUESTDBG_SINGLESTEP_SHIFT, 1f
> + // If we are not doing Single Step we want to prevent the guest doing so
> + // as otherwise we will have to deal with the re-routed exceptions as we
> + // are doing other guest debug related things
> + eor x1, x1, #DBG_SPSR_SS
> + eor x2, x2, #DBG_MDSCR_SS
> +1:
> + msr spsr_el2, x1
> + msr mdscr_el1, x2
> +2:
> // Last bits of the 64bit state
> pop x2, x3
> pop x0, x1
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 523f476..347e5b0 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -7,6 +7,8 @@
> * Note: you must update KVM_API_VERSION if you change this interface.
> */
>
> +#ifndef __ASSEMBLY__
> +
> #include <linux/types.h>
> #include <linux/compiler.h>
> #include <linux/ioctl.h>
> @@ -515,11 +517,6 @@ struct kvm_s390_irq {
> } u;
> };
>
> -/* for KVM_SET_GUEST_DEBUG */
> -
> -#define KVM_GUESTDBG_ENABLE 0x00000001
> -#define KVM_GUESTDBG_SINGLESTEP 0x00000002
> -
> struct kvm_guest_debug {
> __u32 control;
> __u32 pad;
> @@ -1189,4 +1186,15 @@ struct kvm_assigned_msix_entry {
> __u16 padding[3];
> };
>
> +#endif /* __ASSEMBLY__ */
> +
> +/* for KVM_SET_GUEST_DEBUG */
> +
> +#define KVM_GUESTDBG_ENABLE_SHIFT 0
> +#define KVM_GUESTDBG_ENABLE (1 << KVM_GUESTDBG_ENABLE_SHIFT)
> +#define KVM_GUESTDBG_SINGLESTEP_SHIFT 1
> +#define KVM_GUESTDBG_SINGLESTEP (1 << KVM_GUESTDBG_SINGLESTEP_SHIFT)
EALIGN: we can tab these defines up better
> +
> +
> +
> #endif /* __LINUX_KVM_H */
> --
> 2.1.3
>
> _______________________________________________
> kvmarm mailing list
> kvm...@lists.cs.columbia.edu
> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
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