On Wed, Dec 9, 2015 at 5:02 AM, Brian Gerst <brge...@gmail.com> wrote: > Instead of using a duplicate syscall table for the fast path, create stubs for > the syscalls that need pt_regs that save the extra registers if a flag for the > slow path is not set. > > Signed-off-by: Brian Gerst <brge...@gmail.com> > To: Andy Lutomirski <l...@amacapital.net> > Cc: Andy Lutomirski <l...@kernel.org> > Cc: the arch/x86 maintainers <x...@kernel.org> > Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org> > Cc: Borislav Petkov <b...@alien8.de> > Cc: Frédéric Weisbecker <fweis...@gmail.com> > Cc: Denys Vlasenko <dvlas...@redhat.com> > Cc: Linus Torvalds <torva...@linux-foundation.org> > --- > > Applies on top of Andy's syscall cleanup series.
A couple questions: > @@ -306,15 +306,37 @@ END(entry_SYSCALL_64) > > ENTRY(stub_ptregs_64) > /* > - * Syscalls marked as needing ptregs that go through the fast path > - * land here. We transfer to the slow path. > + * Syscalls marked as needing ptregs land here. > + * If we are on the fast path, we need to save the extra regs. > + * If we are on the slow path, the extra regs are already saved. > */ > - DISABLE_INTERRUPTS(CLBR_NONE) > - TRACE_IRQS_OFF > - addq $8, %rsp > - jmp entry_SYSCALL64_slow_path > + movq PER_CPU_VAR(cpu_current_top_of_stack), %r10 > + testl $TS_SLOWPATH, ASM_THREAD_INFO(TI_status, %r10, 0) > + jnz 1f OK (but see below), but why not do: addq $8, %rsp jmp entry_SYSCALL64_slow_path here instead of the stack munging below? > + subq $SIZEOF_PTREGS, %r10 > + SAVE_EXTRA_REGS base=r10 > + movq %r10, %rbx > + call *%rax > + movq %rbx, %r10 > + RESTORE_EXTRA_REGS base=r10 > + ret > +1: > + jmp *%rax > END(stub_ptregs_64) Also, can we not get away with keying off rip or rsp instead of ti->status? That should be faster and less magical IMO. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
