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SEP bit disabled in FC
- From: "Jeffrey Buell" <jbuell vmware com>
- To: <fedora-devel-list redhat com>
- Subject: SEP bit disabled in FC
- Date: Thu, 9 Jun 2005 18:22:05 -0700
In arch/i386/kernel/cpu/common.c:
/* hack: disable SEP for non-NX cpus; SEP breaks Execshield. */
#ifdef CONFIG_HIGHMEM64G
if (!test_bit(X86_FEATURE_NX, c->x86_capability))
#endif
clear_bit(X86_FEATURE_SEP, c->x86_capability);
So, in order to enable Execshield, the SEP cpu bit (sysenter/sysexit) has to
be turned off. But this costs a lot of performance: as much as 2.5X in
syscall-heavy benchmarks (e.g., process tests in lmbench).
How permanent is this hack? Will Execshield be fixed (or removed) by FC5?
Ever? Note that SEP is enabled in SuSE 9.3, for instance.
Jeff
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