On Wed, May 06, 2015 at 05:23:21PM +0100, Alex Bennée wrote:
> This adds support for SW breakpoints inserted by userspace.
>
> We do this by trapping all guest software debug exceptions to the
> hypervisor (MDCR_EL2.TDE). The exit handler sets an exit reason of
> KVM_EXIT_DEBUG with the kvm_debug_exit_arch structure holding the
> exception syndrome information.
>
> It will be up to userspace to extract the PC (via GET_ONE_REG) and
> determine if the debug event was for a breakpoint it inserted. If not
> userspace will need to re-inject the correct exception restart the
> hypervisor to deliver the debug exception to the guest.
>
> Any other guest software debug exception (e.g. single step or HW
> assisted breakpoints) will cause an error and the VM to be killed. This
> is addressed by later patches which add support for the other debug
> types.
>
> Signed-off-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
>
> ---
> v2
> - update to use new exit struct
> - tweak for C setup
> - do our setup in debug_setup/clear code
> - fixed up comments
> v3:
> - fix spacing in KVM_GUESTDBG_VALID_MASK
> - fix and clarify wording on kvm_handle_guest_debug
> - handle error case in kvm_handle_guest_debug
> - re-word the commit message
>
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index 4b0132f..5ef937c 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -2667,7 +2667,7 @@ when running. Common control bits are:
> The top 16 bits of the control field are architecture specific control
> flags which can include the following:
>
> - - KVM_GUESTDBG_USE_SW_BP: using software breakpoints [x86]
> + - KVM_GUESTDBG_USE_SW_BP: using software breakpoints [x86, arm64]
> - KVM_GUESTDBG_USE_HW_BP: using hardware breakpoints [x86, s390]
> - KVM_GUESTDBG_INJECT_DB: inject DB type exception [x86]
> - KVM_GUESTDBG_INJECT_BP: inject BP type exception [x86]
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index 4a274e1..064c105 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -302,7 +302,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
> kvm_arm_set_running_vcpu(NULL);
> }
>
> -#define KVM_GUESTDBG_VALID_MASK (KVM_GUESTDBG_ENABLE)
> +#define KVM_GUESTDBG_VALID_MASK (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP)
>
> /**
> * kvm_arch_vcpu_ioctl_set_guest_debug - set up guest debugging
> diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
> index b1f8731..5bee676 100644
> --- a/arch/arm64/kvm/debug.c
> +++ b/arch/arm64/kvm/debug.c
> @@ -75,6 +75,12 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
> else
> vcpu->arch.mdcr_el2 &= ~MDCR_EL2_TDA;
>
> + /* Trap breakpoints? */
> + if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)
> + vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
> + else
> + vcpu->arch.mdcr_el2 &= ~MDCR_EL2_TDE;
> +
I also don't think you need the else-clause here.
> }
>
> void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 524fa25..27f38a9 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -82,6 +82,40 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run)
> return 1;
> }
>
> +/**
> + * kvm_handle_guest_debug - handle a debug exception instruction
> + *
> + * @vcpu: the vcpu pointer
> + * @run: access to the kvm_run structure for results
> + *
> + * We route all debug exceptions through the same handler. If both the
> + * guest and host are using the same debug facilities it will be up to
> + * userspace to re-inject the correct exception for guest delivery.
> + *
> + * @return: 0 (while setting run->exit_reason), -1 for error
> + */
> +static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu, struct kvm_run *run)
> +{
> + u32 hsr = kvm_vcpu_get_hsr(vcpu);
> + int ret = 0;
> +
> + run->exit_reason = KVM_EXIT_DEBUG;
> + run->debug.arch.hsr = hsr;
> +
> + switch (hsr >> ESR_ELx_EC_SHIFT) {
> + case ESR_ELx_EC_BKPT32:
> + case ESR_ELx_EC_BRK64:
> + break;
> + default:
> + kvm_err("%s: un-handled case hsr: %#08x\n",
> + __func__, (unsigned int) hsr);
> + ret = -1;
> + break;
> + }
> +
> + return ret;
> +}
> +
> static exit_handle_fn arm_exit_handlers[] = {
> [ESR_ELx_EC_WFx] = kvm_handle_wfx,
> [ESR_ELx_EC_CP15_32] = kvm_handle_cp15_32,
> @@ -96,6 +130,8 @@ static exit_handle_fn arm_exit_handlers[] = {
> [ESR_ELx_EC_SYS64] = kvm_handle_sys_reg,
> [ESR_ELx_EC_IABT_LOW] = kvm_handle_guest_abort,
> [ESR_ELx_EC_DABT_LOW] = kvm_handle_guest_abort,
> + [ESR_ELx_EC_BKPT32] = kvm_handle_guest_debug,
> + [ESR_ELx_EC_BRK64] = kvm_handle_guest_debug,
> };
>
> static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu)
> --
> 2.3.5
>
Besides the nit:
Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
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