[PATCH v5 09/17] x86/static_call: Add out-of-line static call implementation

Peter Zijlstra
2020-06-24T15:52:15Z

From: Josh Poimboeuf <jpoimboe@redhat.com>

Add the x86 out-of-line static call implementation. For each key, a
permanent trampoline is created which is the destination for all static
calls for the given key. The trampoline has a direct jump which gets
patched by static_call_update() when the destination function changes.

[peterz: fixed trampoline, rewrote patching code]
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/Kconfig | 1 +
arch/x86/include/asm/static_call.h | 23 +++++++++++++++++++++++
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/static_call.c | 31 +++++++++++++++++++++++++++++++
4 files changed, 56 insertions(+)
create mode 100644 arch/x86/include/asm/static_call.h
create mode 100644 arch/x86/kernel/static_call.c

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -211,6 +211,7 @@ config X86
select HAVE_FUNCTION_ARG_ACCESS_API
select HAVE_STACKPROTECTOR if CC_HAS_SANE_STACKPROTECTOR
select HAVE_STACK_VALIDATION if X86_64
+ select HAVE_STATIC_CALL
select HAVE_RSEQ
select HAVE_SYSCALL_TRACEPOINTS
select HAVE_UNSTABLE_SCHED_CLOCK
--- /dev/null
+++ b/arch/x86/include/asm/static_call.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_STATIC_CALL_H
+#define _ASM_STATIC_CALL_H
+
+#include <asm/text-patching.h>
+
+/*
+ * For CONFIG_HAVE_STATIC_CALL, this is a permanent trampoline which
+ * does a direct jump to the function. The direct jump gets patched by
+ * static_call_update().
+ */
+#define ARCH_DEFINE_STATIC_CALL_TRAMP(name, func) \
+ asm(".pushsection .text, \"ax\" \n" \
+ ".align 4 \n" \
+ ".globl " STATIC_CALL_TRAMP_STR(name) " \n" \
+ STATIC_CALL_TRAMP_STR(name) ": \n" \
+ " .byte 0xe9 # jmp.d32 \n" \
+ " .long " #func " - (. + 4) \n" \
+ ".type " STATIC_CALL_TRAMP_STR(name) ", @function \n" \
+ ".size " STATIC_CALL_TRAMP_STR(name) ", . - " STATIC_CALL_TRAMP_STR(name) " \n" \
+ ".popsection \n")
+
+#endif /* _ASM_STATIC_CALL_H */
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -68,6 +68,7 @@ obj-y += tsc.o tsc_msr.o io_delay.o rt
obj-y += pci-iommu_table.o
obj-y += resource.o
obj-y += irqflags.o
+obj-y += static_call.o

obj-y += process.o
obj-y += fpu/
--- /dev/null
+++ b/arch/x86/kernel/static_call.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/static_call.h>
+#include <linux/memory.h>
+#include <linux/bug.h>
+#include <asm/text-patching.h>
+
+static void __static_call_transform(void *insn, u8 opcode, void *func)
+{
+ const void *code = text_gen_insn(opcode, (long)insn, (long)func);
+
+ if (WARN_ONCE(*(u8 *)insn != opcode,
+ "unexpected static call insn opcode 0x%x at %pS\n",
+ opcode, insn))
+ return;
+
+ if (memcmp(insn, code, CALL_INSN_SIZE) == 0)
+ return;
+
+ text_poke_bp(insn, code, CALL_INSN_SIZE, NULL);
+}
+
+void arch_static_call_transform(void *site, void *tramp, void *func)
+{
+ mutex_lock(&text_mutex);
+
+ if (tramp)
+ __static_call_transform(tramp, JMP32_INSN_OPCODE, func);
+
+ mutex_unlock(&text_mutex);
+}
+EXPORT_SYMBOL_GPL(arch_static_call_transform);