[PATCH v2 08/10] KVM: arm64: guest debug, HW assisted debug support

Alex Bennée
2015-03-31T15:01:27Z

This adds support for userspace to control the HW debug registers for
guest debug. We'll only copy the $ARCH defined number across as that is
all that hyp.S will use anyway. 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.

As QEMU tests for watchpoints based on the address and not the PC we
also need to export the value of far_el2 to userspace.

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

---
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 fro trapping debug register access

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 17d4f9c..ac34093 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2627,7 +2627,7 @@ 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]
@@ -2642,6 +2642,10 @@ 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.
+
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 c1ed8cb..a286026 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -306,6 +306,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)

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

/**
@@ -328,6 +329,26 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
return -EINVAL;

vcpu->guest_debug = dbg->control;
+
+ /* Hardware assisted Break and Watch points */
+ if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) {
+ int nb = get_num_brps();
+ int nw = get_num_wrps();
+
+ /* Copy across up to IMPDEF debug registers to our
+ * shadow copy in the vcpu structure. The debug code
+ * will then set them up before we re-enter the guest.
+ */
+ memcpy(vcpu->arch.guest_debug_regs.dbg_bcr,
+ dbg->arch.dbg_bcr, sizeof(__u64)*nb);
+ memcpy(vcpu->arch.guest_debug_regs.dbg_bvr,
+ dbg->arch.dbg_bvr, sizeof(__u64)*nb);
+ memcpy(vcpu->arch.guest_debug_regs.dbg_wcr,
+ dbg->arch.dbg_wcr, sizeof(__u64)*nw);
+ memcpy(vcpu->arch.guest_debug_regs.dbg_wvr,
+ dbg->arch.dbg_wvr, sizeof(__u64)*nw);
+ }
+
} 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 6a33647..2c359c9 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -106,8 +106,9 @@ struct kvm_vcpu_arch {
/* Exception Information */
struct kvm_vcpu_fault_info fault;

- /* Debug state */
+ /* Guest debug state */
u64 debug_flags;
+ struct kvm_guest_debug_arch guest_debug_regs;

/* Pointer to host CPU context */
kvm_cpu_context_t *host_cpu_context;
@@ -126,6 +127,7 @@ struct kvm_vcpu_arch {
u32 pstate_ss_bit;
u32 mdscr_el1_bits;

+ struct kvm_guest_debug_arch debug_regs;
} debug_saved_regs;

/* Don't run the guest */
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index 6ee70a0..73f21e4 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -118,6 +118,7 @@ struct kvm_guest_debug_arch {
struct kvm_debug_exit_arch {
__u64 pc;
__u32 hsr;
+ __u64 far; /* used for watchpoints */
};

struct kvm_sync_regs {
diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
index 98bbe06..923be44 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 b32362c..3b368f3 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -50,14 +50,19 @@

void kvm_arch_setup_debug(struct kvm_vcpu *vcpu)
{
+ bool trap_debug = false;
+
vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM | MDCR_EL2_TPMCR);
vcpu->arch.mdcr_el2 |= (MDCR_EL2_TDRA | MDCR_EL2_TDOSA);

- /* Trap debug register access? */
+ trace_kvm_arch_setup_debug_reg32("MDCR_EL2", vcpu->arch.mdcr_el2);
+
+ /*
+ * If we are not treating debug registers are dirty we need
+ * to trap if the guest starts accessing them.
+ */
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_debug = true;

/* Is Guest debugging in effect? */
if (vcpu->guest_debug) {
@@ -84,10 +89,69 @@ void kvm_arch_setup_debug(struct kvm_vcpu *vcpu)
vcpu_sys_reg(vcpu, MDSCR_EL1) &= ~DBG_MDSCR_SS;
}

+ /*
+ * HW Break/Watch points
+ */
+ if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) {
+ int nb = get_num_brps();
+ int nw = get_num_wrps();
+ struct kvm_guest_debug_arch *saved, *host;
+
+ vcpu_sys_reg(vcpu, MDSCR_EL1) |=
+ (DBG_MDSCR_KDE|DBG_MDSCR_MDE);
+
+ /*
+ * First we need to make a copy of the guest
+ * debug registers before we wipe them out
+ * with the ones we want to use.
+ */
+ saved = &vcpu_debug_saved_reg(vcpu, debug_regs);
+ host = &vcpu->arch.guest_debug_regs;
+
+ /* Save guest values */
+ memcpy(&saved->dbg_bcr,
+ &vcpu_sys_reg(vcpu, DBGBCR0_EL1),
+ sizeof(__u64)*nb);
+ memcpy(&saved->dbg_bvr,
+ &vcpu_sys_reg(vcpu, DBGBVR0_EL1),
+ sizeof(__u64)*nb);
+ memcpy(&saved->dbg_wcr,
+ &vcpu_sys_reg(vcpu, DBGWCR0_EL1),
+ sizeof(__u64)*nw);
+ memcpy(&saved->dbg_wvr,
+ &vcpu_sys_reg(vcpu, DBGWVR0_EL1),
+ sizeof(__u64)*nw);
+
+ /* Copy in host values */
+ memcpy(&vcpu_sys_reg(vcpu, DBGBCR0_EL1),
+ &host->dbg_bcr,
+ sizeof(__u64)*nb);
+ memcpy(&vcpu_sys_reg(vcpu, DBGBVR0_EL1),
+ &host->dbg_bvr,
+ sizeof(__u64)*nb);
+ memcpy(&vcpu_sys_reg(vcpu, DBGWCR0_EL1),
+ &host->dbg_wcr,
+ sizeof(__u64)*nw);
+ memcpy(&vcpu_sys_reg(vcpu, DBGWVR0_EL1),
+ &host->dbg_wvr,
+ sizeof(__u64)*nw);
+
+ /* Make sure hyp.S copies them in/out */
+ vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_DIRTY;
+ /* Also track guest changes */
+ trap_debug = true;
+ }
+
} else {
/* Debug operations can go straight to the guest */
vcpu->arch.mdcr_el2 &= ~MDCR_EL2_TDE;
}
+
+ /* Trap debug register access? */
+ if (trap_debug)
+ vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
+ else
+ vcpu->arch.mdcr_el2 &= ~MDCR_EL2_TDA;
}

void kvm_arch_clear_debug(struct kvm_vcpu *vcpu)
@@ -100,5 +164,31 @@ void kvm_arch_clear_debug(struct kvm_vcpu *vcpu)
vcpu_sys_reg(vcpu, MDSCR_EL1) &= ~MDSCR_EL1_DEBUG_BITS;
vcpu_sys_reg(vcpu, MDSCR_EL1) |=
vcpu_debug_saved_reg(vcpu, mdscr_el1_bits);
+
+ /*
+ * If we were using HW debug we need to restore the
+ * values the guest had set them up with
+ */
+ if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) {
+ struct kvm_guest_debug_arch *regs;
+ int nb = get_num_brps();
+ int nw = get_num_wrps();
+
+ regs = &vcpu_debug_saved_reg(vcpu, debug_regs);
+
+ /* Restore the saved debug register values */
+ memcpy(&vcpu_sys_reg(vcpu, DBGBCR0_EL1),
+ &regs->dbg_bcr,
+ sizeof(__u64)*nb);
+ memcpy(&vcpu_sys_reg(vcpu, DBGBVR0_EL1),
+ &regs->dbg_bvr,
+ sizeof(__u64)*nb);
+ memcpy(&vcpu_sys_reg(vcpu, DBGWCR0_EL1),
+ &regs->dbg_wcr,
+ sizeof(__u64)*nw);
+ memcpy(&vcpu_sys_reg(vcpu, DBGWVR0_EL1),
+ &regs->dbg_wvr,
+ sizeof(__u64)*nw);
+ }
}
}
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 16accae..460a1aa 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -101,7 +101,11 @@ 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:
run->debug.arch.pc = *vcpu_pc(vcpu);
@@ -129,6 +133,8 @@ 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..c2732c7 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -64,6 +64,12 @@ 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/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index c370b40..be9b188 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -196,16 +196,49 @@ static bool trap_dbgauthstatus_el1(struct kvm_vcpu *vcpu,
* - If the dirty bit is set, save guest registers, restore host
* registers and clear the dirty bit. This ensure that the host can
* now use the debug registers.
+ *
+ * We also use this mechanism to set-up the debug registers for guest
+ * debugging. If this is the case we want to ensure the guest sees
+ * the right versions of the registers - even if they are not going to
+ * be effective while guest debug is using HW debug.
+ *
*/
+
static bool trap_debug_regs(struct kvm_vcpu *vcpu,
const struct sys_reg_params *p,
const struct sys_reg_desc *r)
{
- if (p->is_write) {
- vcpu_sys_reg(vcpu, r->reg) = *vcpu_reg(vcpu, p->Rt);
- vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_DIRTY;
+ if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) {
+ struct kvm_guest_debug_arch *saved;
+ __u64 *val;
+
+ saved = &vcpu_debug_saved_reg(vcpu, debug_regs);
+
+ if (r->reg >= DBGBCR0_EL1 && r->reg <= DBGBCR15_EL1)
+ val = &saved->dbg_bcr[r->reg - DBGBCR0_EL1];
+ else if (r->reg >= DBGBVR0_EL1 && r->reg <= DBGBVR15_EL1)
+ val = &saved->dbg_bvr[r->reg - DBGBVR0_EL1];
+ else if (r->reg >= DBGWCR0_EL1 && r->reg <= DBGWCR15_EL1)
+ val = &saved->dbg_wcr[r->reg - DBGWCR0_EL1];
+ else if (r->reg >= DBGWVR0_EL1 && r->reg <= DBGWVR15_EL1)
+ val = &saved->dbg_wvr[r->reg - DBGWVR0_EL1];
+ else {
+ kvm_err("Bad register index %d\n", r->reg);
+ return false;
+ }
+
+ if (p->is_write)
+ *val = *vcpu_reg(vcpu, p->Rt);
+ else
+ *vcpu_reg(vcpu, p->Rt) = *val;
+
} else {
- *vcpu_reg(vcpu, p->Rt) = vcpu_sys_reg(vcpu, r->reg);
+ if (p->is_write) {
+ vcpu_sys_reg(vcpu, r->reg) = *vcpu_reg(vcpu, p->Rt);
+ vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_DIRTY;
+ } else {
+ *vcpu_reg(vcpu, p->Rt) = vcpu_sys_reg(vcpu, r->reg);
+ }
}

return true;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index ce2db14..0e48c0d 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -771,6 +771,8 @@ struct kvm_ppc_smmu_info {
#define KVM_CAP_PPC_ENABLE_HCALL 104
#define KVM_CAP_CHECK_EXTENSION_VM 105
#define KVM_CAP_S390_USER_SIGP 106
+#define KVM_CAP_GUEST_DEBUG_HW_BPS 107
+#define KVM_CAP_GUEST_DEBUG_HW_WPS 108

#ifdef KVM_CAP_IRQ_ROUTING

--
2.3.4

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