[Xen-devel] [RFC PATCH 3/4] arm/traps: Allow trapping on single-step events

[Sergej Proskurin <proskurin@xxxxxxxxxxxxx>]

This commit concludes the single-stepping functionality on ARM by adding
trapping on and setting up single-stepping events of the architecture.

Signed-off-by: Sergej Proskurin <proskurin@xxxxxxxxxxxxx>
---
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
---
 xen/arch/arm/arm64/entry.S       |  2 ++
 xen/arch/arm/traps.c             | 50 +++++++++++++++++++++++++++++++++++++++-
 xen/include/asm-arm/perfc_defn.h |  1 +
 xen/include/asm-arm/processor.h  |  2 ++
 4 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/arm64/entry.S b/xen/arch/arm/arm64/entry.S
index 6d99e46f0f..5e89f24494 100644
--- a/xen/arch/arm/arm64/entry.S
+++ b/xen/arch/arm/arm64/entry.S
@@ -138,6 +138,8 @@ lr      .req    x30             /* link register */
 
         bl      leave_hypervisor_tail /* Disables interrupts on return */
 
+        bl      setup_single_step
+
         exit_guest \compat
 
         .endif
diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index aa838e8e77..9c45b0706e 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -163,7 +163,7 @@ void init_traps(void)
     WRITE_SYSREG((vaddr_t)hyp_traps_vector, VBAR_EL2);
 
     /* Trap Debug and Performance Monitor accesses */
-    WRITE_SYSREG(HDCR_TDRA|HDCR_TDOSA|HDCR_TDA|HDCR_TPM|HDCR_TPMCR,
+    WRITE_SYSREG(HDCR_TDRA|HDCR_TDOSA|HDCR_TDA|HDCR_TPM|HDCR_TPMCR|HDCR_TDE,
                  MDCR_EL2);
 
     /* Trap CP15 c15 used for implementation defined registers */
@@ -1332,6 +1332,20 @@ int do_bug_frame(struct cpu_user_regs *regs, vaddr_t pc)
 }
 
 #ifdef CONFIG_ARM_64
+static void do_trap_ss(struct cpu_user_regs *regs, const union hsr hsr)
+{
+    int rc = 0;
+
+    /* XXX: We do not support single-stepping of EL2, yet. */
+    BUG_ON(hyp_mode(regs));
+
+    if ( current->domain->arch.monitor.single_step_enabled )
+        rc = monitor_ss();
+
+    if ( rc != 1 )
+        inject_undef_exception(regs, hsr);
+}
+
 static void do_trap_brk(struct cpu_user_regs *regs, const union hsr hsr)
 {
     /* HCR_EL2.TGE and MDCR_EL2.TDE are not set so we never receive
@@ -2943,6 +2957,12 @@ asmlinkage void do_trap_guest_sync(struct cpu_user_regs 
*regs)
         perfc_incr(trap_dabt);
         do_trap_data_abort_guest(regs, hsr);
         break;
+#ifdef CONFIG_ARM_64
+    case HSR_EC_SS_LOWER_EL:
+        perfc_incr(trap_ss);
+        do_trap_ss(regs, hsr);
+        break;
+#endif
 
     default:
         gprintk(XENLOG_WARNING,
@@ -2999,6 +3019,34 @@ asmlinkage void do_trap_fiq(struct cpu_user_regs *regs)
     gic_interrupt(regs, 1);
 }
 
+asmlinkage void setup_single_step(void)
+{
+    uint32_t mdscr, mdcr;
+    struct vcpu *v = current;
+    struct cpu_user_regs *regs = guest_cpu_user_regs();
+
+#define MDSCR_EL1_SS    (_AC(1,U) << 0)
+#define SPSR_EL2_SS     (_AC(1,U) << 21)
+
+    mdscr = READ_SYSREG(MDSCR_EL1);
+    mdcr = READ_SYSREG(MDCR_EL2);
+
+    if ( unlikely(v->arch.single_step) )
+    {
+        mdcr |= HDCR_TDE;
+        mdscr |= MDSCR_EL1_SS;
+        regs->cpsr |= SPSR_EL2_SS;
+    }
+    else
+    {
+        mdcr &= ~HDCR_TDE;
+        mdscr &= ~MDSCR_EL1_SS;
+    }
+
+    WRITE_SYSREG(mdscr, MDSCR_EL1);
+    WRITE_SYSREG(mdcr, MDCR_EL2);
+}
+
 asmlinkage void leave_hypervisor_tail(void)
 {
     while (1)
diff --git a/xen/include/asm-arm/perfc_defn.h b/xen/include/asm-arm/perfc_defn.h
index 5f957ee6ec..46b82e4fee 100644
--- a/xen/include/asm-arm/perfc_defn.h
+++ b/xen/include/asm-arm/perfc_defn.h
@@ -18,6 +18,7 @@ PERFCOUNTER(trap_hvc32,    "trap: 32-bit hvc")
 PERFCOUNTER(trap_smc64,    "trap: 64-bit smc")
 PERFCOUNTER(trap_hvc64,    "trap: 64-bit hvc")
 PERFCOUNTER(trap_sysreg,   "trap: sysreg access")
+PERFCOUNTER(trap_ss,       "trap: software step")
 #endif
 PERFCOUNTER(trap_iabt,     "trap: guest instr abort")
 PERFCOUNTER(trap_dabt,     "trap: guest data abort")
diff --git a/xen/include/asm-arm/processor.h b/xen/include/asm-arm/processor.h
index 9f7a42f86b..3e0ec4f537 100644
--- a/xen/include/asm-arm/processor.h
+++ b/xen/include/asm-arm/processor.h
@@ -323,6 +323,8 @@
 #define HSR_EC_DATA_ABORT_LOWER_EL  0x24
 #define HSR_EC_DATA_ABORT_CURR_EL   0x25
 #ifdef CONFIG_ARM_64
+#define HSR_EC_SS_LOWER_EL          0x32
+#define HSR_EC_SS_CURR_EL           0x33
 #define HSR_EC_BRK                  0x3c
 #endif
 
-- 
2.13.3


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