> On Jun 5, 2019, at 6:08 AM, Peter Zijlstra <pet...@infradead.org> wrote: > > From: Josh Poimboeuf <jpoim...@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. > > Cc: x...@kernel.org > Cc: Steven Rostedt <rost...@goodmis.org> > Cc: Julia Cartwright <ju...@ni.com> > Cc: Ingo Molnar <mi...@kernel.org> > Cc: Ard Biesheuvel <ard.biesheu...@linaro.org> > Cc: Jason Baron <jba...@akamai.com> > Cc: Linus Torvalds <torva...@linux-foundation.org> > Cc: Jiri Kosina <jkos...@suse.cz> > Cc: Thomas Gleixner <t...@linutronix.de> > Cc: Masami Hiramatsu <mhira...@kernel.org> > Cc: Borislav Petkov <b...@alien8.de> > Cc: David Laight <david.lai...@aculab.com> > Cc: Jessica Yu <j...@kernel.org> > Cc: Andy Lutomirski <l...@kernel.org> > Cc: "H. Peter Anvin" <h...@zytor.com> > Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com> > Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> > Link: > https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.kernel.org%2Fr%2F00b08f2194e80241decbf206624b6580b9b8855b.1543200841.git.jpoimboe%40redhat.com&data=02%7C01%7Cnamit%40vmware.com%7C13bc03381930464a018e08d6e9b8f90e%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C636953378007810030&sdata=UnHEUYEYV3FBSZj667lZYzGKRov%2B1PdAjAnM%2BqOz3Ns%3D&reserved=0 > --- > arch/x86/Kconfig | 1 > arch/x86/include/asm/static_call.h | 28 +++++++++++++++++++++++++++ > arch/x86/kernel/Makefile | 1 > arch/x86/kernel/static_call.c | 38 > +++++++++++++++++++++++++++++++++++++ > 4 files changed, 68 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 > @@ -198,6 +198,7 @@ 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 +1,28 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef _ASM_STATIC_CALL_H > +#define _ASM_STATIC_CALL_H > + > +/* > + * Manually construct a 5-byte direct JMP to prevent the assembler from > + * optimizing it into a 2-byte JMP. > + */ > +#define __ARCH_STATIC_CALL_JMP_LABEL(key) ".L" __stringify(key ## _after_jmp) > +#define __ARCH_STATIC_CALL_TRAMP_JMP(key, func) > \ > + ".byte 0xe9 \n" \ > + ".long " #func " - " __ARCH_STATIC_CALL_JMP_LABEL(key) "\n" \ > + __ARCH_STATIC_CALL_JMP_LABEL(key) ":" > + > +/* > + * This is a permanent trampoline which does a direct jump to the function. > + * The direct jump get patched by static_call_update(). > + */ > +#define ARCH_DEFINE_STATIC_CALL_TRAMP(key, func) \ > + asm(".pushsection .text, \"ax\" \n" \ > + ".align 4 \n" \ > + ".globl " STATIC_CALL_TRAMP_STR(key) " \n" \ > + ".type " STATIC_CALL_TRAMP_STR(key) ", @function \n" \ > + STATIC_CALL_TRAMP_STR(key) ": \n" \ > + __ARCH_STATIC_CALL_TRAMP_JMP(key, func) " \n" \ > + ".popsection \n") > + > +#endif /* _ASM_STATIC_CALL_H */ > --- a/arch/x86/kernel/Makefile > +++ b/arch/x86/kernel/Makefile > @@ -63,6 +63,7 @@ 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 +1,38 @@ > +// SPDX-License-Identifier: GPL-2.0 > +#include <linux/static_call.h> > +#include <linux/memory.h> > +#include <linux/bug.h> > +#include <asm/text-patching.h> > +#include <asm/nospec-branch.h> > + > +#define CALL_INSN_SIZE 5 > + > +void arch_static_call_transform(void *site, void *tramp, void *func) > +{ > + unsigned char opcodes[CALL_INSN_SIZE]; > + unsigned char insn_opcode; > + unsigned long insn; > + s32 dest_relative; > + > + mutex_lock(&text_mutex); > + > + insn = (unsigned long)tramp; > + > + insn_opcode = *(unsigned char *)insn; > + if (insn_opcode != 0xE9) { > + WARN_ONCE(1, "unexpected static call insn opcode 0x%x at %pS", > + insn_opcode, (void *)insn); > + goto unlock;
This might happen if a kprobe is installed on the call, no? I don’t know if you want to be more gentle handling of this case (or perhaps modify can_probe() to prevent such a case).
