[Qemu-arm] [PATCH v10 4/6] target-arm: kvm - add support for HW assisted debug

[Alex Bennée]

This adds basic support for HW assisted debug. The ioctl interface to
KVM allows us to pass an implementation defined number of break and
watch point registers. When KVM_GUESTDBG_USE_HW is specified these
debug registers will be installed in place on the world switch into the
guest.

The hardware is actually capable of more advanced matching but it is
unclear if this expressiveness is available via the gdbstub protocol.

Signed-off-by: Alex Bennée <address@hidden>

---
v2
  - correct setting of PMC/BAS/MASK
  - improved commentary
  - added helper function to check watchpoint in range
  - fix find/deletion of watchpoints
v3
  - use internals.h definitions
v6
  - KVM_GUESTDBG_USE_HW_BP->KVM_GUESTDBG_USE_HW
  - renamed some helper functions to avoid confusion
v9
  - fix merge conflicts on re-base
  - rm asm/ptrace.h include
  - add additional commentry for hw breakpoints
  - explain gdb's model for HW bkpts
  - fix up spacing, formatting as per checkpatch
  - better PAC values
  - use is_power_of_2
  - use _arm_ fn naming and add docs
  - add a CPUWatchpoint structure for reporting
  - replace manual array manipulation with g_array abstraction
v10
  - fix compilation for arm32/split imps between kvm32/64
  - make find_hw_watchpoint/breakpoint local static functions
  - cleaned up comment grammar
  - fixed up missing spaces
  - removed pointless ?: booleanisation
  - removed pointless kvm_arm_hw_debug_active wrappers
  - s/is/if/
---
 target-arm/kvm.c     |  26 +---
 target-arm/kvm32.c   |  29 +++++
 target-arm/kvm64.c   | 361 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 target-arm/kvm_arm.h |  21 +++
 4 files changed, 415 insertions(+), 22 deletions(-)

diff --git a/target-arm/kvm.c b/target-arm/kvm.c
index 7f44e22..84974bb 100644
--- a/target-arm/kvm.c
+++ b/target-arm/kvm.c
@@ -566,26 +566,12 @@ void kvm_arch_update_guest_debug(CPUState *cs, struct 
kvm_guest_debug *dbg)
         dbg->control |= KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP;
     }
 #endif
-}
-
-int kvm_arch_insert_hw_breakpoint(target_ulong addr,
-                                  target_ulong len, int type)
-{
-    qemu_log_mask(LOG_UNIMP, "%s: not implemented\n", __func__);
-    return -EINVAL;
-}
-
-int kvm_arch_remove_hw_breakpoint(target_ulong addr,
-                                  target_ulong len, int type)
-{
-    qemu_log_mask(LOG_UNIMP, "%s: not implemented\n", __func__);
-    return -EINVAL;
-}
-
-
-void kvm_arch_remove_all_hw_breakpoints(void)
-{
-    qemu_log_mask(LOG_UNIMP, "%s: not implemented\n", __func__);
+#ifdef KVM_GUESTDBG_USE_HW
+    if (kvm_arm_hw_debug_active(cs)) {
+        dbg->control |= KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_HW;
+        kvm_arm_copy_hw_debug_data(&dbg->arch);
+    }
+#endif
 }
 
 void kvm_arch_init_irq_routing(KVMState *s)
diff --git a/target-arm/kvm32.c b/target-arm/kvm32.c
index 5ce969f..ff83ce6 100644
--- a/target-arm/kvm32.c
+++ b/target-arm/kvm32.c
@@ -493,3 +493,32 @@ bool kvm_arm_handle_debug(CPUState *cs, struct 
kvm_debug_exit_arch *debug_exit)
     qemu_log_mask(LOG_UNIMP, "%s: guest debug not yet implemented\n", 
__func__);
     return false;
 }
+
+int kvm_arch_insert_hw_breakpoint(target_ulong addr,
+                                  target_ulong len, int type)
+{
+    qemu_log_mask(LOG_UNIMP, "%s: not implemented\n", __func__);
+    return -EINVAL;
+}
+
+int kvm_arch_remove_hw_breakpoint(target_ulong addr,
+                                  target_ulong len, int type)
+{
+    qemu_log_mask(LOG_UNIMP, "%s: not implemented\n", __func__);
+    return -EINVAL;
+}
+
+void kvm_arch_remove_all_hw_breakpoints(void)
+{
+    qemu_log_mask(LOG_UNIMP, "%s: not implemented\n", __func__);
+}
+
+void kvm_arm_copy_hw_debug_data(struct kvm_guest_debug_arch *ptr)
+{
+    qemu_log_mask(LOG_UNIMP, "%s: not implemented\n", __func__);
+}
+
+bool kvm_arm_hw_debug_active(CPUState *cs)
+{
+    return false;
+}
diff --git a/target-arm/kvm64.c b/target-arm/kvm64.c
index 5f96cde..771ecdb 100644
--- a/target-arm/kvm64.c
+++ b/target-arm/kvm64.c
@@ -2,6 +2,7 @@
  * ARM implementation of KVM hooks, 64 bit specific code
  *
  * Copyright Mian-M. Hamayun 2013, Virtual Open Systems
+ * Copyright Alex Bennée 2014, Linaro
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  * See the COPYING file in the top-level directory.
@@ -12,13 +13,17 @@
 #include <sys/types.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
+#include <sys/ptrace.h>
 
+#include <linux/elf.h>
 #include <linux/kvm.h>
 
 #include "config-host.h"
 #include "qemu-common.h"
 #include "qemu/timer.h"
 #include "qemu/error-report.h"
+#include "qemu/host-utils.h"
+#include "exec/gdbstub.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/kvm.h"
 #include "kvm_arm.h"
@@ -28,20 +33,358 @@
 
 static bool have_guest_debug;
 
+/*
+ * Although the ARM implementation of hardware assisted debugging
+ * allows for different breakpoints per-core, the current GDB
+ * interface treats them as a global pool of registers (which seems to
+ * be the case for x86, ppc and s390). As a result we store one copy
+ * of registers which is used for all active cores.
+ *
+ * Write access is serialised by virtue of the GDB protocol which
+ * updates things. Read access (i.e. when the values are copied to the
+ * vCPU) is also gated by GDB's run control.
+ *
+ * This is not unreasonable as most of the time debugging kernels you
+ * never know which core will eventually execute your function.
+ */
+
+typedef struct {
+    uint64_t bcr;
+    uint64_t bvr;
+} HWBreakpoint;
+
+/* The watchpoint registers can cover more area than the requested
+ * watchpoint so we need to store the additional information
+ * somewhere. We also need to supply a CPUWatchpoint to the GDB stub
+ * when the watchpoint is hit.
+ */
+typedef struct {
+    uint64_t wcr;
+    uint64_t wvr;
+    CPUWatchpoint details;
+} HWWatchpoint;
+
+/* Maximum and current break/watch point counts */
+int max_hw_bps, max_hw_wps;
+GArray *hw_breakpoints, *hw_watchpoints;
+
+#define cur_hw_wps      (hw_watchpoints->len)
+#define cur_hw_bps      (hw_breakpoints->len)
+#define get_hw_bp(i)    (&g_array_index(hw_breakpoints, HWBreakpoint, i))
+#define get_hw_wp(i)    (&g_array_index(hw_watchpoints, HWWatchpoint, i))
+
 /**
- * kvm_arm_init_debug()
+ * kvm_arm_init_debug() - check for guest debug capabilities
  * @cs: CPUState
  *
- * Check for guest debug capabilities.
+ * kvm_check_extension returns the number of debug registers we have
+ * or 0 if we have none.
  *
  */
 static void kvm_arm_init_debug(CPUState *cs)
 {
     have_guest_debug = kvm_check_extension(cs->kvm_state,
                                            KVM_CAP_SET_GUEST_DEBUG);
+
+    max_hw_wps = kvm_check_extension(cs->kvm_state, 
KVM_CAP_GUEST_DEBUG_HW_WPS);
+    hw_watchpoints = g_array_sized_new(true, true,
+                                       sizeof(HWWatchpoint), max_hw_wps);
+
+    max_hw_bps = kvm_check_extension(cs->kvm_state, 
KVM_CAP_GUEST_DEBUG_HW_BPS);
+    hw_breakpoints = g_array_sized_new(true, true,
+                                       sizeof(HWBreakpoint), max_hw_bps);
     return;
 }
 
+/**
+ * insert_hw_breakpoint()
+ * @addr: address of breakpoint
+ *
+ * See ARM ARM D2.9.1 for details but here we are only going to create
+ * simple un-linked breakpoints (i.e. we don't chain breakpoints
+ * together to match address and context or vmid). The hardware is
+ * capable of fancier matching but that will require exposing that
+ * fanciness to GDB's interface
+ *
+ * D7.3.2 DBGBCR<n>_EL1, Debug Breakpoint Control Registers
+ *
+ *  31  24 23  20 19   16 15 14  13  12   9 8   5 4    3 2   1  0
+ * +------+------+-------+-----+----+------+-----+------+-----+---+
+ * | RES0 |  BT  |  LBN  | SSC | HMC| RES0 | BAS | RES0 | PMC | E |
+ * +------+------+-------+-----+----+------+-----+------+-----+---+
+ *
+ * BT: Breakpoint type (0 = unlinked address match)
+ * LBN: Linked BP number (0 = unused)
+ * SSC/HMC/PMC: Security, Higher and Priv access control (Table D-12)
+ * BAS: Byte Address Select (RES1 for AArch64)
+ * E: Enable bit
+ */
+static int insert_hw_breakpoint(target_ulong addr)
+{
+    HWBreakpoint brk = {
+        .bcr = 0x1,                             /* BCR E=1, enable */
+        .bvr = addr
+    };
+
+    if (cur_hw_bps >= max_hw_bps) {
+        return -ENOBUFS;
+    }
+
+    brk.bcr = deposit32(brk.bcr, 1, 2, 0x3);   /* PMC = 11 */
+    brk.bcr = deposit32(brk.bcr, 5, 4, 0xf);   /* BAS = RES1 */
+
+    g_array_append_val(hw_breakpoints, brk);
+
+    return 0;
+}
+
+/**
+ * delete_hw_breakpoint()
+ * @pc: address of breakpoint
+ *
+ * Delete a breakpoint and shuffle any above down
+ */
+
+static int delete_hw_breakpoint(target_ulong pc)
+{
+    int i;
+    for (i = 0; i < hw_breakpoints->len; i++) {
+        HWBreakpoint *brk = get_hw_bp(i);
+        if (brk->bvr == pc) {
+            g_array_remove_index(hw_breakpoints, i);
+            return 0;
+        }
+    }
+    return -ENOENT;
+}
+
+/**
+ * insert_hw_watchpoint()
+ * @addr: address of watch point
+ * @len: size of area
+ * @type: type of watch point
+ *
+ * See ARM ARM D2.10. As with the breakpoints we can do some advanced
+ * stuff if we want to. The watch points can be linked with the break
+ * points above to make them context aware. However for simplicity
+ * currently we only deal with simple read/write watch points.
+ *
+ * D7.3.11 DBGWCR<n>_EL1, Debug Watchpoint Control Registers
+ *
+ *  31  29 28   24 23  21  20  19 16 15 14  13   12  5 4   3 2   1  0
+ * +------+-------+------+----+-----+-----+-----+-----+-----+-----+---+
+ * | RES0 |  MASK | RES0 | WT | LBN | SSC | HMC | BAS | LSC | PAC | E |
+ * +------+-------+------+----+-----+-----+-----+-----+-----+-----+---+
+ *
+ * MASK: num bits addr mask (0=none,01/10=res,11=3 bits (8 bytes))
+ * WT: 0 - unlinked, 1 - linked (not currently used)
+ * LBN: Linked BP number (not currently used)
+ * SSC/HMC/PAC: Security, Higher and Priv access control (Table D2-11)
+ * BAS: Byte Address Select
+ * LSC: Load/Store control (01: load, 10: store, 11: both)
+ * E: Enable
+ *
+ * The bottom 2 bits of the value register are masked. Therefore to
+ * break on any sizes smaller than an unaligned word you need to set
+ * MASK=0, BAS=bit per byte in question. For larger regions (^2) you
+ * need to ensure you mask the address as required and set BAS=0xff
+ */
+
+static int insert_hw_watchpoint(target_ulong addr,
+                                target_ulong len, int type)
+{
+    HWWatchpoint wp = {
+        .wcr = 1, /* E=1, enable */
+        .wvr = addr & (~0x7ULL),
+        .details = { .vaddr = addr, .len = len }
+    };
+
+    if (cur_hw_wps >= max_hw_wps) {
+        return -ENOBUFS;
+    }
+
+    /*
+     * HMC=0 SSC=0 PAC=3 will hit EL0 or EL1, any security state,
+     * valid whether EL3 is implemented or not
+     */
+    wp.wcr = deposit32(wp.wcr, 1, 2, 3);
+
+    switch (type) {
+    case GDB_WATCHPOINT_READ:
+        wp.wcr = deposit32(wp.wcr, 3, 2, 1);
+        wp.details.flags = BP_MEM_READ;
+        break;
+    case GDB_WATCHPOINT_WRITE:
+        wp.wcr = deposit32(wp.wcr, 3, 2, 2);
+        wp.details.flags = BP_MEM_WRITE;
+        break;
+    case GDB_WATCHPOINT_ACCESS:
+        wp.wcr = deposit32(wp.wcr, 3, 2, 3);
+        wp.details.flags = BP_MEM_ACCESS;
+        break;
+    default:
+        g_assert_not_reached();
+        break;
+    }
+    if (len <= 8) {
+        /* we align the address and set the bits in BAS */
+        int off = addr & 0x7;
+        int bas = (1 << len) - 1;
+
+        wp.wcr = deposit32(wp.wcr, 5 + off, 8 - off, bas);
+    } else {
+        /* For ranges above 8 bytes we need to be a power of 2 */
+        if (is_power_of_2(len)) {
+            int bits = ctz64(len);
+
+            wp.wvr &= ~((1 << bits) - 1);
+            wp.wcr = deposit32(wp.wcr, 24, 4, bits);
+            wp.wcr = deposit32(wp.wcr, 5, 8, 0xff);
+        } else {
+            return -ENOBUFS;
+        }
+    }
+
+    g_array_append_val(hw_watchpoints, wp);
+    return 0;
+}
+
+
+static bool check_watchpoint_in_range(int i, target_ulong addr)
+{
+    HWWatchpoint *wp = get_hw_wp(i);
+    uint64_t addr_top, addr_bottom = wp->wvr;
+    int bas = extract32(wp->wcr, 5, 8);
+    int mask = extract32(wp->wcr, 24, 4);
+
+    if (mask) {
+        addr_top = addr_bottom + (1 << mask);
+    } else {
+        /* BAS must be contiguous but can offset against the base
+         * address in DBGWVR */
+        addr_bottom = addr_bottom + ctz32(bas);
+        addr_top = addr_bottom + clo32(bas);
+    }
+
+    if (addr >= addr_bottom && addr <= addr_top) {
+        return true;
+    }
+
+    return false;
+}
+
+/**
+ * delete_hw_watchpoint()
+ * @addr: address of breakpoint
+ *
+ * Delete a breakpoint and shuffle any above down
+ */
+
+static int delete_hw_watchpoint(target_ulong addr,
+                                target_ulong len, int type)
+{
+    int i;
+    for (i = 0; i < cur_hw_wps; i++) {
+        if (check_watchpoint_in_range(i, addr)) {
+            g_array_remove_index(hw_watchpoints, i);
+            return 0;
+        }
+    }
+    return -ENOENT;
+}
+
+
+int kvm_arch_insert_hw_breakpoint(target_ulong addr,
+                                  target_ulong len, int type)
+{
+    switch (type) {
+    case GDB_BREAKPOINT_HW:
+        return insert_hw_breakpoint(addr);
+        break;
+    case GDB_WATCHPOINT_READ:
+    case GDB_WATCHPOINT_WRITE:
+    case GDB_WATCHPOINT_ACCESS:
+        return insert_hw_watchpoint(addr, len, type);
+    default:
+        return -ENOSYS;
+    }
+}
+
+int kvm_arch_remove_hw_breakpoint(target_ulong addr,
+                                  target_ulong len, int type)
+{
+    switch (type) {
+    case GDB_BREAKPOINT_HW:
+        return delete_hw_breakpoint(addr);
+        break;
+    case GDB_WATCHPOINT_READ:
+    case GDB_WATCHPOINT_WRITE:
+    case GDB_WATCHPOINT_ACCESS:
+        return delete_hw_watchpoint(addr, len, type);
+    default:
+        return -ENOSYS;
+    }
+}
+
+
+void kvm_arch_remove_all_hw_breakpoints(void)
+{
+    if (cur_hw_wps > 0) {
+        g_array_remove_range(hw_watchpoints, 0, cur_hw_wps);
+    }
+    if (cur_hw_bps > 0) {
+        g_array_remove_range(hw_breakpoints, 0, cur_hw_bps);
+    }
+}
+
+void kvm_arm_copy_hw_debug_data(struct kvm_guest_debug_arch *ptr)
+{
+    int i;
+    memset(ptr, 0, sizeof(struct kvm_guest_debug_arch));
+
+    for (i = 0; i < max_hw_wps; i++) {
+        HWWatchpoint *wp = get_hw_wp(i);
+        ptr->dbg_wcr[i] = wp->wcr;
+        ptr->dbg_wvr[i] = wp->wvr;
+    }
+    for (i = 0; i < max_hw_bps; i++) {
+        HWBreakpoint *bp = get_hw_bp(i);
+        ptr->dbg_bcr[i] = bp->bcr;
+        ptr->dbg_bvr[i] = bp->bvr;
+    }
+}
+
+bool kvm_arm_hw_debug_active(CPUState *cs)
+{
+    return ((cur_hw_wps > 0) || (cur_hw_bps > 0));
+}
+
+static bool find_hw_breakpoint(CPUState *cpu, target_ulong pc)
+{
+    int i;
+
+    for (i = 0; i < cur_hw_bps; i++) {
+        HWBreakpoint *bp = get_hw_bp(i);
+        if (bp->bvr == pc) {
+            return true;
+        }
+    }
+    return false;
+}
+
+static CPUWatchpoint *find_hw_watchpoint(CPUState *cpu, target_ulong addr)
+{
+    int i;
+
+    for (i = 0; i < cur_hw_wps; i++) {
+        if (check_watchpoint_in_range(i, addr)) {
+            return &get_hw_wp(i)->details;
+        }
+    }
+    return NULL;
+}
+
+
 static inline void set_feature(uint64_t *features, int feature)
 {
     *features |= 1ULL << feature;
@@ -546,6 +889,20 @@ bool kvm_arm_handle_debug(CPUState *cs, struct 
kvm_debug_exit_arch *debug_exit)
             return true;
         }
         break;
+    case EC_BREAKPOINT:
+        if (find_hw_breakpoint(cs, env->pc)) {
+            return true;
+        }
+        break;
+    case EC_WATCHPOINT:
+    {
+        CPUWatchpoint *wp = find_hw_watchpoint(cs, debug_exit->far);
+        if (wp) {
+            cs->watchpoint_hit = wp;
+            return true;
+        }
+        break;
+    }
     default:
         error_report("%s: unhandled debug exit (%"PRIx32", %"PRIx64")\n",
                      __func__, debug_exit->hsr, env->pc);
diff --git a/target-arm/kvm_arm.h b/target-arm/kvm_arm.h
index 88f5b37..962b3bd 100644
--- a/target-arm/kvm_arm.h
+++ b/target-arm/kvm_arm.h
@@ -224,4 +224,25 @@ const char *gicv3_class_name(void);
  */
 bool kvm_arm_handle_debug(CPUState *cs, struct kvm_debug_exit_arch 
*debug_exit);
 
+/**
+ * kvm_arm_hw_debug_active:
+ * @cs: CPU State
+ *
+ * Return: TRUE if any hardware breakpoints in use.
+ */
+
+bool kvm_arm_hw_debug_active(CPUState *cs);
+
+/**
+ * kvm_arm_copy_hw_debug_data:
+ *
+ * @ptr: kvm_guest_debug_arch structure
+ *
+ * Copy the architecture specific debug registers into the
+ * kvm_guest_debug ioctl structure.
+ */
+struct kvm_guest_debug_arch;
+
+void kvm_arm_copy_hw_debug_data(struct kvm_guest_debug_arch *ptr);
+
 #endif
-- 
2.6.3