[PATCH v2 06/10] KVM: arm64: guest debug, add SW break point support

Alex Bennée
2015-03-31T15:01:21Z

This adds support for SW breakpoints inserted by userspace.

We do this by trapping all BKPT exceptions in the
hypervisor (MDCR_EL2_TDE). The kvm_debug_exit_arch carries the address
of the exception. If user-space doesn't know of the breakpoint then we
have a guest inserted breakpoint and the hypervisor needs to start again
and deliver the exception to guest.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

---
v2
- update to use new exit struct
- tweak for C setup
- do our setup in debug_setup/clear code
- fixed up comments

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 06c5064..17d4f9c 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2626,7 +2626,7 @@ 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 7ea8b0e..d3bc8dc 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -304,7 +304,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
kvm_arm_set_running_vcpu(NULL);
}

-#define KVM_GUESTDBG_VALID (KVM_GUESTDBG_ENABLE)
+#define KVM_GUESTDBG_VALID (KVM_GUESTDBG_ENABLE|KVM_GUESTDBG_USE_SW_BP)

int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
struct kvm_guest_debug *dbg)
diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index 8a29d0b..cff0475 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -45,11 +45,18 @@ void kvm_arch_setup_debug(struct kvm_vcpu *vcpu)
vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM | MDCR_EL2_TPMCR);
vcpu->arch.mdcr_el2 |= (MDCR_EL2_TDRA | MDCR_EL2_TDOSA);

+ /* Trap debug register access? */
if (!vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY)
vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
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;
+
}

void kvm_arch_clear_debug(struct kvm_vcpu *vcpu)
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 524fa25..ed1bbb4 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -82,6 +82,37 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run)
return 1;
}

+/**
+ * kvm_handle_debug_exception - 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 as we
+ * just need to report the PC and the HSR values to userspace.
+ * Userspace may decide to re-inject the exception and deliver it to
+ * the guest if it wasn't for the host to deal with.
+ */
+static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu, struct kvm_run *run)
+{
+ u32 hsr = kvm_vcpu_get_hsr(vcpu);
+
+ 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:
+ run->debug.arch.pc = *vcpu_pc(vcpu);
+ break;
+ default:
+ kvm_err("%s: un-handled case hsr: %#08x\n",
+ __func__, (unsigned int) hsr);
+ break;
+ }
+ return 0;
+}
+
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 +127,8 @@ 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)
--
2.3.4

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