[PATCH RFC 07/19] perf tools: Workaround missing maps for x86_64 KPTI entry trampolines

[Adrian Hunter]

On x86_64 the KPTI entry trampolines are not in the kernel map created by
perf tools. That results in the addresses having no symbols and prevents
annotation. It also causes Intel PT to have decoding errors at the
trampoline addresses. Workaround that by creating maps for the trampolines.
At present the kernel does not export information revealing where the
trampolines are. Until that happens, the addresses are hardcoded.

Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
---
 tools/perf/util/machine.c | 104 ++++++++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/machine.h |   3 ++
 tools/perf/util/symbol.c  |  12 +++---
 3 files changed, 114 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 22047ff3cf2a..1bf15aa0b099 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -851,6 +851,110 @@ static int machine__get_running_kernel_start(struct machine *machine,
 	return 0;
 }
 
+struct special_kernal_map {
+	u64 start;
+	u64 end;
+	u64 pgoff;
+};
+
+static int machine__create_special_kernel_map(struct machine *machine,
+					      struct dso *kernel,
+					      struct special_kernal_map *sm)
+{
+	struct kmap *kmap;
+	struct map *map;
+
+	map = map__new2(sm->start, kernel);
+	if (!map)
+		return -1;
+
+	map->end   = sm->end;
+	map->pgoff = sm->pgoff;
+
+	kmap = map__kmap(map);
+
+	kmap->kmaps = &machine->kmaps;
+
+	map_groups__insert(&machine->kmaps, map);
+
+	pr_debug2("Added special kernel map %" PRIx64 "-%" PRIx64 "\n",
+		  map->start, map->end);
+
+	map__put(map);
+
+	return 0;
+}
+
+static u64 find_entry_trampoline(struct dso *dso)
+{
+	struct {
+		const char *name;
+		u64 addr;
+	} syms[] = {
+		/* Duplicates are removed so lookup all aliases */
+		{"_entry_trampoline", 0},
+		{"__entry_trampoline_start", 0},
+		{"entry_SYSCALL_64_trampoline", 0},
+	};
+	struct symbol *sym = dso__first_symbol(dso);
+	unsigned int i;
+
+	for (; sym; sym = dso__next_symbol(sym)) {
+		if (sym->binding != STB_GLOBAL)
+			continue;
+		for (i = 0; i < ARRAY_SIZE(syms); i++) {
+			if (!strcmp(sym->name, syms[i].name))
+				syms[i].addr = sym->start;
+		}
+	}
+
+	for (i = 0; i < ARRAY_SIZE(syms); i++) {
+		if (syms[i].addr)
+			return syms[i].addr;
+	}
+
+	return 0;
+}
+
+/*
+ * These values can be used for kernels that do not have symbols for the entry
+ * trampolines in kallsyms.
+ */
+#define X86_64_CPU_ENTRY_AREA_PER_CPU	0xfffffe0000000000ULL
+#define X86_64_CPU_ENTRY_AREA_SIZE	0x2c000
+#define X86_64_ENTRY_TRAMPOLINE		0x6000
+
+/* Map x86_64 KPTI entry trampolines */
+int machine__map_x86_64_entry_trampolines(struct machine *machine,
+					  struct dso *kernel)
+{
+	u64 pgoff = find_entry_trampoline(kernel);
+	int nr_cpus_avail = 0, cpu;
+
+	if (!pgoff)
+		return 0;
+
+	if (machine->env)
+		nr_cpus_avail = machine->env->nr_cpus_avail;
+
+	/* Add a 1 page map for each CPU's entry trampoline */
+	for (cpu = 0; cpu < nr_cpus_avail; cpu++) {
+		u64 va = X86_64_CPU_ENTRY_AREA_PER_CPU +
+			 cpu * X86_64_CPU_ENTRY_AREA_SIZE +
+			 X86_64_ENTRY_TRAMPOLINE;
+		struct special_kernal_map sm = {
+			.start = va,
+			.end   = va + page_size,
+			.pgoff = pgoff,
+		};
+
+		if (machine__create_special_kernel_map(machine, kernel, &sm) < 0)
+			return -1;
+	}
+
+	return 0;
+}
+
 static int
 __machine__create_kernel_maps(struct machine *machine, struct dso *kernel)
 {
diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
index b31d33b5aa2a..6e1c63d3a625 100644
--- a/tools/perf/util/machine.h
+++ b/tools/perf/util/machine.h
@@ -267,4 +267,7 @@ int machine__set_current_tid(struct machine *machine, int cpu, pid_t pid,
  */
 char *machine__resolve_kernel_addr(void *vmachine, unsigned long long *addrp, char **modp);
 
+int machine__map_x86_64_entry_trampolines(struct machine *machine,
+					  struct dso *kernel);
+
 #endif /* __PERF_MACHINE_H */
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 4a39f4d0a174..c3a1a89a61cb 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -1490,20 +1490,22 @@ int dso__load(struct dso *dso, struct map *map)
 		goto out;
 	}
 
+	if (map->groups && map->groups->machine)
+		machine = map->groups->machine;
+	else
+		machine = NULL;
+
 	if (dso->kernel) {
 		if (dso->kernel == DSO_TYPE_KERNEL)
 			ret = dso__load_kernel_sym(dso, map);
 		else if (dso->kernel == DSO_TYPE_GUEST_KERNEL)
 			ret = dso__load_guest_kernel_sym(dso, map);
 
+		if (machine && machine__is(machine, "x86_64"))
+			machine__map_x86_64_entry_trampolines(machine, dso);
 		goto out;
 	}
 
-	if (map->groups && map->groups->machine)
-		machine = map->groups->machine;
-	else
-		machine = NULL;
-
 	dso->adjust_symbols = 0;
 
 	if (perfmap) {
-- 
1.9.1