[PATCH v5 10/12] KVM: arm64: guest debug, HW assisted debug support

From: Alex BennÃe
Date: Fri May 29 2015 - 05:51:09 EST

This adds support for userspace to control the HW debug registers for
guest debug. In the debug ioctl we copy the IMPDEF defined number of
registers into a new register set called host_debug_state. There is now
a new vcpu parameter called debug_ptr which selects which register set
is to copied into the real registers when world switch occurs.

I've moved some helper functions into the hw_breakpoint.h header for
re-use.

As with single step we need to tweak the guest registers to enable the
exceptions so we need to save and restore those bits.

Two new capabilities have been added to the KVM_EXTENSION ioctl to allow
userspace to query the number of hardware break and watch points
available on the host hardware.

Signed-off-by: Alex BennÃe <alex.bennee@xxxxxxxxxx>

---
v2
- switched to C setup
- replace host debug registers directly into context
- minor tweak to api docs
- setup right register for debug
- add FAR_EL2 to debug exit structure
- add support for trapping debug register access
v3
- remove stray trace statement
- fix spacing around operators (various)
- clean-up usage of trap_debug
- introduce debug_ptr, replace excessive memcpy stuff
- don't use memcpy in ioctl, just assign
- update cap ioctl documentation
- reword a number comments
- rename host_debug_state->external_debug_state
v4
- use the new u32/u64 split debug_ptr approach
- fix some wording/comments
v5
- don't set MDSCR_EL1.KDE (not needed)
---
Documentation/virtual/kvm/api.txt | 7 ++++++-
arch/arm/kvm/arm.c | 7 +++++++
arch/arm64/include/asm/hw_breakpoint.h | 12 +++++++++++
arch/arm64/include/asm/kvm_host.h | 3 ++-
arch/arm64/include/uapi/asm/kvm.h | 2 +-
arch/arm64/kernel/hw_breakpoint.c | 12 -----------
arch/arm64/kvm/debug.c | 37 +++++++++++++++++++++++++++++-----
arch/arm64/kvm/handle_exit.c | 6 ++++++
arch/arm64/kvm/reset.c | 12 +++++++++++
include/uapi/linux/kvm.h | 2 ++
10 files changed, 80 insertions(+), 20 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 33c8143..ada57df 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2668,7 +2668,7 @@ 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, arm64]
- - KVM_GUESTDBG_USE_HW_BP: using hardware breakpoints [x86, s390]
+ - KVM_GUESTDBG_USE_HW_BP: using hardware breakpoints [x86, s390, arm64]
- KVM_GUESTDBG_INJECT_DB: inject DB type exception [x86]
- KVM_GUESTDBG_INJECT_BP: inject BP type exception [x86]
- KVM_GUESTDBG_EXIT_PENDING: trigger an immediate guest exit [s390]
@@ -2683,6 +2683,11 @@ updated to the correct (supplied) values.
The second part of the structure is architecture specific and
typically contains a set of debug registers.

+For arm64 the number of debug registers is implementation defined and
+can be determined by querying the KVM_CAP_GUEST_DEBUG_HW_BPS and
+KVM_CAP_GUEST_DEBUG_HW_WPS capabilities which return a positive number
+indicating the number of supported registers.
+
When debug events exit the main run loop with the reason
KVM_EXIT_DEBUG with the kvm_debug_exit_arch part of the kvm_run
structure containing architecture specific debug information.
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 0d17c7b..6df47c1 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -307,6 +307,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)

#define KVM_GUESTDBG_VALID_MASK (KVM_GUESTDBG_ENABLE | \
KVM_GUESTDBG_USE_SW_BP | \
+ KVM_GUESTDBG_USE_HW_BP | \
KVM_GUESTDBG_SINGLESTEP)

/**
@@ -327,6 +328,12 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,

if (dbg->control & KVM_GUESTDBG_ENABLE) {
vcpu->guest_debug = dbg->control;
+
+ /* Hardware assisted Break and Watch points */
+ if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) {
+ vcpu->arch.external_debug_state = dbg->arch;
+ }
+
} else {
/* If not enabled clear all flags */
vcpu->guest_debug = 0;
diff --git a/arch/arm64/include/asm/hw_breakpoint.h b/arch/arm64/include/asm/hw_breakpoint.h
index 52b484b..c450552 100644
--- a/arch/arm64/include/asm/hw_breakpoint.h
+++ b/arch/arm64/include/asm/hw_breakpoint.h
@@ -130,6 +130,18 @@ static inline void ptrace_hw_copy_thread(struct task_struct *task)
}
#endif

+/* Determine number of BRP registers available. */
+static inline int get_num_brps(void)
+{
+ return ((read_cpuid(ID_AA64DFR0_EL1) >> 12) & 0xf) + 1;
+}
+
+/* Determine number of WRP registers available. */
+static inline int get_num_wrps(void)
+{
+ return ((read_cpuid(ID_AA64DFR0_EL1) >> 20) & 0xf) + 1;
+}
+
extern struct pmu perf_ops_bp;

#endif /* __KERNEL__ */
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index e5040b6..498d4f7 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -113,12 +113,13 @@ struct kvm_vcpu_arch {

/*
* For debugging the guest we need to keep a set of debug
- * registers which can override the guests own debug state
+ * registers which can override the guest's own debug state
* while being used. These are set via the KVM_SET_GUEST_DEBUG
* ioctl.
*/
struct kvm_guest_debug_arch *debug_ptr;
struct kvm_guest_debug_arch vcpu_debug_state;
+ struct kvm_guest_debug_arch external_debug_state;

/* Pointer to host CPU context */
kvm_cpu_context_t *host_cpu_context;
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index 43758e7..95168c2 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -116,7 +116,7 @@ struct kvm_guest_debug_arch {

struct kvm_debug_exit_arch {
__u32 hsr;
- __u64 far;
+ __u64 far; /* used for watchpoints */
};

/*
diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
index e7d934d..3a41bbf 100644
--- a/arch/arm64/kernel/hw_breakpoint.c
+++ b/arch/arm64/kernel/hw_breakpoint.c
@@ -49,18 +49,6 @@ static DEFINE_PER_CPU(int, stepping_kernel_bp);
static int core_num_brps;
static int core_num_wrps;

-/* Determine number of BRP registers available. */
-static int get_num_brps(void)
-{
- return ((read_cpuid(ID_AA64DFR0_EL1) >> 12) & 0xf) + 1;
-}
-
-/* Determine number of WRP registers available. */
-static int get_num_wrps(void)
-{
- return ((read_cpuid(ID_AA64DFR0_EL1) >> 20) & 0xf) + 1;
-}
-
int hw_breakpoint_slots(int type)
{
/*
diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index 10a6baa..3c0daae 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -98,10 +98,6 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
MDCR_EL2_TDRA |
MDCR_EL2_TDOSA);

- /* Trap on access to debug registers? */
- if (trap_debug)
- vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
-
/* Is Guest debugging in effect? */
if (vcpu->guest_debug) {
vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
@@ -124,11 +120,42 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
} else {
vcpu_sys_reg(vcpu, MDSCR_EL1) &= ~DBG_MDSCR_SS;
}
+
+ /*
+ * HW Break/Watch points
+ *
+ * We simply switch the debug_ptr to point to our new
+ * external_debug_state which has been populated by the
+ * debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY
+ * mechanism ensures the registers are updated on the
+ * world switch.
+ */
+ if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) {
+ /* Enable breakpoints/watchpoints */
+ vcpu_sys_reg(vcpu, MDSCR_EL1) |= DBG_MDSCR_MDE;
+
+ vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
+ vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_DIRTY;
+ trap_debug = true;
+ }
}
+
+ /* Trap debug register access */
+ if (trap_debug)
+ vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
}

void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
{
- if (vcpu->guest_debug)
+ if (vcpu->guest_debug) {
restore_guest_debug_regs(vcpu);
+
+ /*
+ * If we were using HW debug we need to restore the
+ * debug_ptr to the guest debug state.
+ */
+ if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
+ vcpu->arch.debug_ptr = &vcpu->arch.vcpu_debug_state;
+
+ }
}
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index e9de13e..68a0759 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -103,7 +103,11 @@ static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu, struct kvm_run *run)
run->debug.arch.hsr = hsr;

switch (hsr >> ESR_ELx_EC_SHIFT) {
+ case ESR_ELx_EC_WATCHPT_LOW:
+ run->debug.arch.far = vcpu->arch.fault.far_el2;
+ /* fall through */
case ESR_ELx_EC_SOFTSTP_LOW:
+ case ESR_ELx_EC_BREAKPT_LOW:
case ESR_ELx_EC_BKPT32:
case ESR_ELx_EC_BRK64:
break;
@@ -132,6 +136,8 @@ static exit_handle_fn arm_exit_handlers[] = {
[ESR_ELx_EC_IABT_LOW] = kvm_handle_guest_abort,
[ESR_ELx_EC_DABT_LOW] = kvm_handle_guest_abort,
[ESR_ELx_EC_SOFTSTP_LOW]= kvm_handle_guest_debug,
+ [ESR_ELx_EC_WATCHPT_LOW]= kvm_handle_guest_debug,
+ [ESR_ELx_EC_BREAKPT_LOW]= kvm_handle_guest_debug,
[ESR_ELx_EC_BKPT32] = kvm_handle_guest_debug,
[ESR_ELx_EC_BRK64] = kvm_handle_guest_debug,
};
diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index 0b43265..21d5a62 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -56,6 +56,12 @@ static bool cpu_has_32bit_el1(void)
return !!(pfr0 & 0x20);
}

+/**
+ * kvm_arch_dev_ioctl_check_extension
+ *
+ * We currently assume that the number of HW registers is uniform
+ * across all CPUs (see cpuinfo_sanity_check).
+ */
int kvm_arch_dev_ioctl_check_extension(long ext)
{
int r;
@@ -64,6 +70,12 @@ int kvm_arch_dev_ioctl_check_extension(long ext)
case KVM_CAP_ARM_EL1_32BIT:
r = cpu_has_32bit_el1();
break;
+ case KVM_CAP_GUEST_DEBUG_HW_BPS:
+ r = get_num_brps();
+ break;
+ case KVM_CAP_GUEST_DEBUG_HW_WPS:
+ r = get_num_wrps();
+ break;
default:
r = 0;
}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 70ac641..f020dd0 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -817,6 +817,8 @@ struct kvm_ppc_smmu_info {
#define KVM_CAP_S390_INJECT_IRQ 113
#define KVM_CAP_S390_IRQ_STATE 114
#define KVM_CAP_PPC_HWRNG 115
+#define KVM_CAP_GUEST_DEBUG_HW_BPS 116
+#define KVM_CAP_GUEST_DEBUG_HW_WPS 117

#ifdef KVM_CAP_IRQ_ROUTING

--
2.4.1

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