Re: Intel P6 vs P7 system call performance

[Jamie Lokier]

Ingo Molnar wrote:
> and i'm 100% sure the more robust eflags saving will also avoid security
> holes. The amount of security-relevant complexity that comes from all the
> x86 features [and their combinations] is amazing.

Userspace can skip the "popfl" with a well-timed signal.  If the
"sysexit" path leaves the kernel with an unsafe eflags, that will
propagate into the signal handler.

AFAICT, one of these is required:

	1. eflags must be safe before leaving kernel space, or
	2. setup_sigcontext() must clean it up (it already does clear TF).

-- Jamie