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Re: [PATCH v2 22/36] x86/entry: Add C code for fast system call entries

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On Tue, Oct 6, 2015 at 1:48 AM, Andy Lutomirski <luto@kernel.org> wrote:
> This handles both SYSENTER and SYSCALL.  The asm glue will take care
> of the differences.

This seems non-optimal.

> +__visible void do_fast_syscall_32(struct pt_regs *regs)

.. so this is the fast case on 32-bit, but:

> +       local_irq_enable();
> +       if (get_user(*(u32 *)&regs->cx,
> +                    (u32 __user __force *)(unsigned long)(u32)regs->sp)) {
...
> +       local_irq_disable();

this is expensive. Since we now do it in C code and can easily do
this, why does the code not do this all with interrupts disabled,
which is valid for user accesses but disables page faults, and then in
the unlikely situation where that fails, we do it the slow and careful
way?

It would be nice to see this patch series not just get rid of asm
code, but also do things to optimize cases that used to be annoyingly
hard to do in user space. No?

         Linus
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[PATCH v2 00/36] x86: Rewrite all syscall entries except native 64-bit Andy Lutomirski <luto@kernel.org> - 2015-10-06 03:00 +0200
  [PATCH v2 04/36] selftests/x86: Add a test for syscall restart and arg modification Andy Lutomirski <luto@kernel.org> - 2015-10-06 03:00 +0200
    [tip:x86/asm] selftests/x86:   Add a test for ptrace syscall restart and arg modification tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2015-10-07 18:20 +0200
  [PATCH v2 20/36] x86/entry: Add do_syscall_32, a C function to do 32-bit syscalls Andy Lutomirski <luto@kernel.org> - 2015-10-06 03:00 +0200
    [tip:x86/asm] x86/entry: Add do_syscall_32(),   a C function to do 32-bit syscalls tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2015-10-09 15:20 +0200
  [PATCH v2 13/36] x86/vdso/32: Save extra registers in the INT80 vsyscall path Andy Lutomirski <luto@kernel.org> - 2015-10-06 03:00 +0200
    [tip:x86/asm] x86/vdso/32:   Save extra registers in the INT80 vsyscall path tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2015-10-09 15:10 +0200
  [PATCH v2 11/36] x86/vdso: Replace hex int80 CFI annotations with gas directives Andy Lutomirski <luto@kernel.org> - 2015-10-06 03:00 +0200
    [tip:x86/asm] x86/vdso:   Replace hex int80 CFI annotations with GAS directives tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2015-10-09 15:10 +0200
  [PATCH v2 02/36] x86/uaccess: __chk_range_not_ok is unlikely to return true Andy Lutomirski <luto@kernel.org> - 2015-10-06 03:00 +0200
    Re: [PATCH v2 02/36] x86/uaccess: __chk_range_not_ok is unlikely to  return true Borislav Petkov <bp@alien8.de> - 2015-10-07 13:00 +0200
      Re: [PATCH v2 02/36] x86/uaccess: __chk_range_not_ok is unlikely to  return true Ingo Molnar <mingo@kernel.org> - 2015-10-07 18:30 +0200
    [tip:x86/asm] x86/uaccess: Add unlikely() to __chk_range_not_ok()   failure paths tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2015-10-07 18:20 +0200
  [PATCH v2 06/36] x86/entry: Move lockdep_sys_exit to prepare_exit_to_usermode Andy Lutomirski <luto@kernel.org> - 2015-10-06 03:00 +0200
    [tip:x86/asm] x86/entry, locking/lockdep: Move lockdep_sys_exit()   to prepare_exit_to_usermode() tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2015-10-07 18:20 +0200
      Re: [tip:x86/asm] x86/entry, locking/lockdep: Move  lockdep_sys_exit() to prepare_exit_to_usermode() Peter Zijlstra <peterz@infradead.org> - 2015-10-08 11:00 +0200
        Re: [tip:x86/asm] x86/entry, locking/lockdep: Move lockdep_sys_exit()  to prepare_exit_to_usermode() Andy Lutomirski <luto@amacapital.net> - 2015-10-09 21:40 +0200
  [PATCH v2 16/36] x86/entry/64/compat: Remove most of the fast system call machinery Andy Lutomirski <luto@kernel.org> - 2015-10-06 03:00 +0200
    [tip:x86/asm] x86/entry/64/compat:   Remove most of the fast system call machinery tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2015-10-09 15:20 +0200
  [PATCH v2 22/36] x86/entry: Add C code for fast system call entries Andy Lutomirski <luto@kernel.org> - 2015-10-06 03:00 +0200
    Re: [PATCH v2 22/36] x86/entry: Add C code for fast system call entries Linus Torvalds <torvalds@linux-foundation.org> - 2015-10-06 10:30 +0200
      Re: [PATCH v2 22/36] x86/entry: Add C code for fast system call entries Andy Lutomirski <luto@amacapital.net> - 2015-10-06 20:30 +0200
    Re: [PATCH v2 22/36] x86/entry: Add C code for fast system call entries Linus Torvalds <torvalds@linux-foundation.org> - 2015-10-06 10:30 +0200
    [tip:x86/asm] x86/entry: Add C code for fast system call entries tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2015-10-09 15:20 +0200
  [PATCH v2 30/36] x86/entry: Make irqs_disabled checks in exit code depend on lockdep Andy Lutomirski <luto@kernel.org> - 2015-10-06 03:00 +0200
    [tip:x86/asm] x86/entry:   Make irqs_disabled checks in exit code depend on lockdep tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2015-10-09 15:20 +0200
  [PATCH v2 15/36] x86/entry/64/compat: Remove audit optimizations Andy Lutomirski <luto@kernel.org> - 2015-10-06 03:00 +0200
    [tip:x86/asm] x86/entry/64/compat: Remove audit optimizations tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2015-10-09 15:20 +0200
  [PATCH v2 32/36] x86/entry: Micro-optimize compat fast syscall arg fetch Andy Lutomirski <luto@kernel.org> - 2015-10-06 03:00 +0200
    Re: [PATCH v2 32/36] x86/entry: Micro-optimize compat fast syscall  arg fetch Ingo Molnar <mingo@kernel.org> - 2015-10-09 09:40 +0200
      Re: [PATCH v2 32/36] x86/entry: Micro-optimize compat fast syscall  arg fetch Andy Lutomirski <luto@amacapital.net> - 2015-10-09 21:30 +0200
        Re: [PATCH v2 32/36] x86/entry: Micro-optimize compat fast syscall  arg fetch Ingo Molnar <mingo@kernel.org> - 2015-10-10 11:10 +0200
    [tip:x86/asm] x86/entry:   Micro-optimize compat fast syscall arg fetch tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2015-10-09 15:20 +0200
  Re: [PATCH v2 00/36] x86: Rewrite all syscall entries except native 64-bit Linus Torvalds <torvalds@linux-foundation.org> - 2015-10-06 10:40 +0200
    Re: [PATCH v2 00/36] x86: Rewrite all syscall entries except native  64-bit Ingo Molnar <mingo@kernel.org> - 2015-10-06 11:00 +0200
    Re: [PATCH v2 00/36] x86: Rewrite all syscall entries except native 64-bit Andy Lutomirski <luto@amacapital.net> - 2015-10-06 20:30 +0200
  Re: [PATCH v2 00/36] x86: Rewrite all syscall entries except native  64-bit Ingo Molnar <mingo@kernel.org> - 2015-10-09 15:10 +0200
    Re: [PATCH v2 00/36] x86: Rewrite all syscall entries except native 64-bit Richard Weinberger <richard.weinberger@gmail.com> - 2015-10-12 20:40 +0200
      Re: [PATCH v2 00/36] x86: Rewrite all syscall entries except native 64-bit Andy Lutomirski <luto@amacapital.net> - 2015-10-12 20:50 +0200
        Re: [PATCH v2 00/36] x86: Rewrite all syscall entries except native  64-bit Richard Weinberger <richard@nod.at> - 2015-10-12 23:10 +0200

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