cachepc

commit ca3b348013267bf727ba52bb6fc97a7ab7d367dc
parent dbb1ac88094516d1165c9e43c4a79cbc3a18d7d1
Author: Louis Burda <quent.burda@gmail.com>
Date:   Thu,  2 Feb 2023 17:39:09 -0600

Debug single-stepping on page-boundaries in page_step

Diffstat:
M
Makefile
 | 
1
+
M
cachepc/cachepc.h
 | 
5
+++--
M
cachepc/const.h
 | 
7
+++++--
M
cachepc/kvm.c
 | 
5
+++--
M
cachepc/macro.S
 | 
6
++----
M
cachepc/uapi.h
 | 
3
+++
M
test/kvm-pagestep.c
 | 
1
+
M
test/kvm-pagestep_guest.S
 | 
2
+-

8 files changed, 19 insertions(+), 11 deletions(-)
diff --git a/Makefile b/Makefile
@@ -60,6 +60,7 @@ load:
 
 prep:
 	sudo sh -c "echo 0 > /proc/sys/kernel/watchdog"
+	sudo sh -c "echo performance > /sys/devices/system/cpu/cpu2/cpufreq/scaling_governor"
 	sudo sh -c "echo 1500000 > /sys/devices/system/cpu/cpu2/cpufreq/scaling_min_freq"
 	sudo sh -c "echo 1500000 > /sys/devices/system/cpu/cpu2/cpufreq/scaling_max_freq"
 	sudo sh -c "echo 1500000 > /sys/devices/system/cpu/cpu2/cpufreq/scaling_min_freq"
diff --git a/cachepc/cachepc.h b/cachepc/cachepc.h
@@ -37,6 +37,7 @@ struct cpc_fault {
 };
 
 struct cpc_track_pages {
+	bool singlestep_resolve;
 	bool prev_avail;
 	bool cur_avail;
 	bool next_avail;
@@ -99,8 +100,8 @@ extern bool cpc_singlestep;
 extern bool cpc_singlestep_reset;
 extern bool cpc_long_step;
 
-extern volatile bool cpc_apic_oneshot;
-extern uint32_t cpc_apic_timer;
+extern bool cpc_apic_oneshot;
+extern int32_t cpc_apic_timer;
 
 extern uint32_t cpc_track_mode;
 extern uint64_t cpc_track_start_gfn;
diff --git a/cachepc/const.h b/cachepc/const.h
@@ -20,8 +20,11 @@
 #define CPC_CL_PREV_OFFSET 8
 #define CPC_CL_COUNT_OFFSET 16
 
-#define CPC_APIC_TIMER_TDCR APIC_TDR_DIV_2 // APIC_TDR_DIV_1
+/* APIC divisor determines how much time is added per increment.
+ * A large divisor decreases the counter slower, which means more time
+ * is added for each increment, possiblpy skipping whole instructions */
+#define CPC_APIC_TIMER_TDCR APIC_TDR_DIV_1
 #define CPC_APIC_TIMER_SOFTDIV 1
-#define CPC_APIC_TIMER_MIN (100 * CPC_APIC_TIMER_SOFTDIV)
+#define CPC_APIC_TIMER_MIN (20 * CPC_APIC_TIMER_SOFTDIV)
 
 #define CPC_EVENT_BATCH_MAX 1000
diff --git a/cachepc/kvm.c b/cachepc/kvm.c
@@ -59,8 +59,8 @@ EXPORT_SYMBOL(cpc_singlestep);
 EXPORT_SYMBOL(cpc_singlestep_reset);
 EXPORT_SYMBOL(cpc_long_step);
 
-volatile bool cpc_apic_oneshot = false;
-uint32_t cpc_apic_timer = 0;
+bool cpc_apic_oneshot = false;
+int32_t cpc_apic_timer = 0;
 EXPORT_SYMBOL(cpc_apic_oneshot);
 EXPORT_SYMBOL(cpc_apic_timer);
 
@@ -485,6 +485,7 @@ cpc_track_mode_ioctl(void __user *arg_user)
 		break;
 	case CPC_TRACK_PAGES:
 		memset(&cpc_track_pages, 0, sizeof(cpc_track_pages));
+		cpc_track_pages.singlestep_resolve = cfg.pages.singlestep_resolve;
 		cpc_track_all(vcpu, KVM_PAGE_TRACK_EXEC);
 		break;
 	case CPC_TRACK_STEPS:
diff --git a/cachepc/macro.S b/cachepc/macro.S
@@ -2,10 +2,8 @@
 
 # clobbers rax, rbx, rcx, rdx
 .macro barrier
-    mfence # memory barrier
-    rdtsc # serializing
-    # mov $0x80000005, %rax
-    # cpuid # serializing (cpuid alone does not work)
+    mfence # finish load and stores
+    lfence # prevent reordering
 .endm
 
 # clobbers rax, rbx, rcx, rdx, (out)
diff --git a/cachepc/uapi.h b/cachepc/uapi.h
@@ -72,6 +72,9 @@ struct cpc_track_cfg {
 			__u8 use_filter;
 			__u8 with_data;
 		} steps;
+		struct {
+			__u8 singlestep_resolve;
+		} pages;
 	};
 };
 
diff --git a/test/kvm-pagestep.c b/test/kvm-pagestep.c
@@ -111,6 +111,7 @@ main(int argc, const char **argv)
 
 		memset(&cfg, 0, sizeof(cfg));
 		cfg.mode = CPC_TRACK_PAGES;
+		cfg.pages.singlestep_resolve = true;
 		ret = ioctl(kvm_dev, KVM_CPC_TRACK_MODE, &cfg);
 		if (ret) err(1, "KVM_CPC_TRACK_MODE");
 
diff --git a/test/kvm-pagestep_guest.S b/test/kvm-pagestep_guest.S
@@ -17,7 +17,7 @@ guest:
 .rept L1_LINESIZE * L1_SETS - 2
     nop
 .endr
-    cpuid # two byte instruction
+    rdtsc # two byte instruction
 .endr
 # ---------------------------------