On Fri, 7 Jun 2019 06:13:58 +0000 Nadav Amit <na...@vmware.com> wrote:
> > 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). > Perhaps it is better to block kprobes from attaching to a static call. Or have it use the static call directly as it does with ftrace. But that would probably be much more work. -- Steve
