On Tue, Jul 07, 2015 at 03:51:29AM -0700, tip-bot for Andy Lutomirski wrote: > Commit-ID: feed36cde0a10adb957445a37e48f957f30b2273 > Gitweb: http://git.kernel.org/tip/feed36cde0a10adb957445a37e48f957f30b2273 > Author: Andy Lutomirski <[email protected]> > AuthorDate: Fri, 3 Jul 2015 12:44:25 -0700 > Committer: Ingo Molnar <[email protected]> > CommitDate: Tue, 7 Jul 2015 10:59:06 +0200 > > x86/entry: Add enter_from_user_mode() and use it in syscalls > > Changing the x86 context tracking hooks is dangerous because > there are no good checks that we track our context correctly. > Add a helper to check that we're actually in CONTEXT_USER when > we enter from user mode and wire it up for syscall entries. > > Subsequent patches will wire this up for all non-NMI entries as > well. NMIs are their own special beast and cannot currently > switch overall context tracking state. Instead, they have their > own special RCU hooks. > > This is a tiny speedup if !CONFIG_CONTEXT_TRACKING (removes a > branch) and a tiny slowdown if CONFIG_CONTEXT_TRACING (adds a > layer of indirection). Eventually, we should fix up the core > context tracking code to supply a function that does what we > want (and can be much simpler than user_exit), which will enable > us to get rid of the extra call. > > Signed-off-by: Andy Lutomirski <[email protected]> > Cc: Andy Lutomirski <[email protected]> > Cc: Borislav Petkov <[email protected]> > Cc: Brian Gerst <[email protected]> > Cc: Denys Vlasenko <[email protected]> > Cc: Denys Vlasenko <[email protected]> > Cc: Frederic Weisbecker <[email protected]> > Cc: H. Peter Anvin <[email protected]> > Cc: Kees Cook <[email protected]> > Cc: Linus Torvalds <[email protected]> > Cc: Oleg Nesterov <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Rik van Riel <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: [email protected] > Link: > http://lkml.kernel.org/r/853b42420066ec3fb856779cdc223a6dcb5d355b.1435952415.git.l...@kernel.org > Signed-off-by: Ingo Molnar <[email protected]> > --- > arch/x86/entry/common.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c > index 917d0c3..9a327ee 100644 > --- a/arch/x86/entry/common.c > +++ b/arch/x86/entry/common.c > @@ -28,6 +28,15 @@ > #define CREATE_TRACE_POINTS > #include <trace/events/syscalls.h> > > +#ifdef CONFIG_CONTEXT_TRACKING > +/* Called on entry from user mode with IRQs off. */ > +__visible void enter_from_user_mode(void) > +{ > + CT_WARN_ON(ct_state() != CONTEXT_USER); > + user_exit(); > +} > +#endif > + > static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) > { > #ifdef CONFIG_X86_64 > @@ -65,14 +74,16 @@ unsigned long syscall_trace_enter_phase1(struct pt_regs > *regs, u32 arch) > work = ACCESS_ONCE(current_thread_info()->flags) & > _TIF_WORK_SYSCALL_ENTRY; > > +#ifdef CONFIG_CONTEXT_TRACKING > /* > * If TIF_NOHZ is set, we are required to call user_exit() before > * doing anything that could touch RCU. > */ > if (work & _TIF_NOHZ) { > - user_exit(); > + enter_from_user_mode(); > work &= ~_TIF_NOHZ;
We should move the sanity check to user_exit/enter() and use user_exit/enter() only when we actually enter/exit user. Here it's the case but syscall_trace_leave() and do_notify_resume() are special case that should probably use exception_enter/exit() unless your patchset have changed things such that there is only one call to user_exit() once we completed everything before resuming userspace. I need to review the rest of the patchset to discover that :-) > } > +#endif > > #ifdef CONFIG_SECCOMP > /* -- 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/
