On Oct 16, 2015 7:54 PM, "Brian Gerst" <[email protected]> wrote: > > On Fri, Oct 16, 2015 at 6:42 PM, Andy Lutomirski <[email protected]> wrote: > > When I rewrote entry_INT80_32, I thought that int80 was an interrupt > > gate. It's a trap gate. *facepalm* > > > > Thanks to Brian Gerst for pointing out that it's better to change > > the entry code than to change the gate type. > > > > Suggested-by: Brian Gerst <[email protected]> > > Reported-by: Borislav Petkov <[email protected]> > > Fixes: 150ac78d63af ("x86/entry/32: Switch INT80 to the new C syscall path") > > Signed-off-by: Andy Lutomirski <[email protected]> > > --- > > arch/x86/entry/common.c | 15 ++++++++++++--- > > arch/x86/entry/entry_32.S | 8 ++++---- > > arch/x86/entry/entry_64_compat.S | 2 +- > > 3 files changed, 17 insertions(+), 8 deletions(-) > > > > diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c > > index b53e04d301a3..09afb3b6acbb 100644 > > --- a/arch/x86/entry/common.c > > +++ b/arch/x86/entry/common.c > > @@ -351,7 +351,14 @@ __visible inline void syscall_return_slowpath(struct > > pt_regs *regs) > > * in workloads that use it, and it's usually called from > > * do_fast_syscall_32, so forcibly inline it to improve performance. > > */ > > -static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs) > > +#ifdef CONFIG_X86_32 > > +/* 32-bit kernels use a trap gate for int80, and the asm code calls here. > > */ > > +__visible > > +#else > > +/* 64-bit kernels use do_syscall_32_irqs_off instead. */ > > +static > > +#endif > > +__always_inline void do_syscall_32_irqs_on(struct pt_regs *regs) > > { > > struct thread_info *ti = pt_regs_to_thread_info(regs); > > unsigned int nr = (unsigned int)regs->orig_ax; > > @@ -386,12 +393,14 @@ static __always_inline void > > do_syscall_32_irqs_on(struct pt_regs *regs) > > syscall_return_slowpath(regs); > > } > > > > -/* Handles int $0x80 */ > > -__visible void do_int80_syscall_32(struct pt_regs *regs) > > +#ifdef CONFIG_X86_64 > > +/* Handles int $0x80 on 64-bit kernels */ > > +__visible void do_syscall_32_irqs_off(struct pt_regs *regs) > > { > > local_irq_enable(); > > do_syscall_32_irqs_on(regs); > > } > > +#endif > > This would be more readable if the STI were moved down into the asm > for 64-bit. In fact, we should be re-enabling interrupts as early as > possible once the full kernel environment is set up (on the process > stack, NT clear, and after SWAPGS). What was your reasoning for > moving it later?
On x86_64, we have to use an interrupt gate because of swapgs, and for context tracking, once I clean up the SYSCALL64 entry, I want to make it all the way to user_exit with IRQs off. There are nice optimizations that become possible once user_exit is always called with IRQs off, and there's another cleanup we can do when IRQs are no longer possible in kernel mode with IRQs on. For x86_32, we don't actually support context tracking, but we could. So maybe we should suck up the ~3 cycles for int80 users and just use an interrupt gate everywhere. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
