[PATCH 4/7] KVM: arm64: guest debug, add SW break point support
From: Alex BennÃe
Date: Tue Nov 25 2014 - 11:34:03 EST
This adds support for SW breakpoints inserted by userspace.
First we need to trap all BKPT exceptions in the hypervisor (ELS). This
in controlled through the MDCR_EL2 register. I've added a new field to
the vcpu structure to hold this value. There should be scope to
rationlise this with the VCPU_DEBUG_FLAGS/KVM_ARM64_DEBUG_DIRTY_SHIFT
manipulation in later patches.
Once the exception arrives we triggers an exit from the main hypervisor
loop to the hypervisor controller. The kvm_debug_exit_arch carries the
address of the exception. If the controller doesn't know of 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 BennÃe <alex.bennee@xxxxxxxxxx>
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 2c6386e..9383359 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2592,7 +2592,7 @@ 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 a0ff410..48d26bb 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -303,6 +303,9 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
struct kvm_guest_debug *dbg)
{
+ /* Route debug traps to el2? */
+ bool route_el2 = false;
+
/* If it's not enabled clear all flags */
if (!(dbg->control & KVM_GUESTDBG_ENABLE)) {
vcpu->guest_debug = 0;
@@ -320,8 +323,8 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
/* Software Break Points */
if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP) {
- kvm_info("SW BP support requested, not yet implemented\n");
- return -EINVAL;
+ kvm_info("SW BP support requested\n");
+ route_el2 = true;
}
/* Hardware assisted Break and Watch points */
@@ -330,6 +333,20 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
return -EINVAL;
}
+ /* If we are going to handle any debug exceptions we need to
+ * set MDCE_EL2.TDE to ensure they are routed to the
+ * hypervisor. If userspace determines the exception was
+ * actually internal to the guest it needs to handle
+ * re-injecting the exception.
+ */
+ if (route_el2) {
+ kvm_info("routing debug exceptions");
+ vcpu->arch.mdcr_el2 = MDCR_EL2_TDE;
+ } else {
+ kvm_info("not routing debug exceptions");
+ vcpu->arch.mdcr_el2 = 0;
+ }
+
return 0;
}
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 2012c4b..38b0f07 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -98,6 +98,7 @@ struct kvm_vcpu_arch {
/* HYP configuration */
u64 hcr_el2;
+ u32 mdcr_el2;
/* Exception Information */
struct kvm_vcpu_fault_info fault;
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 9a9fce0..8da1043 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -122,6 +122,7 @@ int main(void)
DEFINE(VCPU_HPFAR_EL2, offsetof(struct kvm_vcpu, arch.fault.hpfar_el2));
DEFINE(VCPU_DEBUG_FLAGS, offsetof(struct kvm_vcpu, arch.debug_flags));
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));
DEFINE(VCPU_HOST_CONTEXT, offsetof(struct kvm_vcpu, arch.host_cpu_context));
DEFINE(VCPU_TIMER_CNTV_CTL, offsetof(struct kvm_vcpu, arch.timer_cpu.cntv_ctl));
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 34b8bd0..28dc92b 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -71,6 +71,26 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run)
return 1;
}
+/**
+ * kvm_handle_bkpt - handle a break-point instruction
+ *
+ * @vcpu: the vcpu pointer
+ *
+ * By definition if we arrive here it's because we are routing
+ * all SW breakpoints to the hyper-visor as some may be a result of
+ * guest debugging. If user-space decides this particular break-point
+ * isn't for the host to handle it can re-feed the exception to the
+ * guest.
+ */
+static int kvm_handle_bkpt(struct kvm_vcpu *vcpu, struct kvm_run *run)
+{
+ run->exit_reason = KVM_EXIT_DEBUG;
+ run->debug.arch.exit_type = KVM_DEBUG_EXIT_SW_BKPT;
+ run->debug.arch.address = *vcpu_pc(vcpu);
+ kvm_info("exiting from %llx\n", run->debug.arch.address);
+ 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,
@@ -85,6 +105,8 @@ 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_BKPT32] = kvm_handle_bkpt,
+ [ESR_EL2_EC_BRK64] = kvm_handle_bkpt,
};
static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu)
diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
index b72aa9f..3c733ea 100644
--- a/arch/arm64/kvm/hyp.S
+++ b/arch/arm64/kvm/hyp.S
@@ -772,6 +772,10 @@
orr x2, x2, #(MDCR_EL2_TPM | MDCR_EL2_TPMCR)
orr x2, x2, #(MDCR_EL2_TDRA | MDCR_EL2_TDOSA)
+ // Any other bits (currently TDE)
+ ldr x3, [x0, #VCPU_MDCR_EL2]
+ orr x2, x2, x3
+
// Check for KVM_ARM64_DEBUG_DIRTY, and set debug to trap
// if not dirty.
ldr x3, [x0, #VCPU_DEBUG_FLAGS]
--
2.1.3
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