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authorTejun Heo <tj@kernel.org>2009-02-09 16:17:40 +0300
committerIngo Molnar <mingo@elte.hu>2009-02-10 02:42:00 +0300
commitccbeed3a05908d201b47b6c3dd1a373138bba566 (patch)
treee834d548c70426aa3885dd2169be1a79be4a617b /arch/x86/lguest
parentd9a89a26e02ef9ed03f74a755a8b4d8f3a066622 (diff)
downloadlinux-ccbeed3a05908d201b47b6c3dd1a373138bba566.tar.xz
x86: make lazy %gs optional on x86_32
Impact: pt_regs changed, lazy gs handling made optional, add slight overhead to SAVE_ALL, simplifies error_code path a bit On x86_32, %gs hasn't been used by kernel and handled lazily. pt_regs doesn't have place for it and gs is saved/loaded only when necessary. In preparation for stack protector support, this patch makes lazy %gs handling optional by doing the followings. * Add CONFIG_X86_32_LAZY_GS and place for gs in pt_regs. * Save and restore %gs along with other registers in entry_32.S unless LAZY_GS. Note that this unfortunately adds "pushl $0" on SAVE_ALL even when LAZY_GS. However, it adds no overhead to common exit path and simplifies entry path with error code. * Define different user_gs accessors depending on LAZY_GS and add lazy_save_gs() and lazy_load_gs() which are noop if !LAZY_GS. The lazy_*_gs() ops are used to save, load and clear %gs lazily. * Define ELF_CORE_COPY_KERNEL_REGS() which always read %gs directly. xen and lguest changes need to be verified. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jeremy Fitzhardinge <jeremy@xensource.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/lguest')
-rw-r--r--arch/x86/lguest/boot.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 19e33b6cd593..da2e314f61b5 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -283,7 +283,7 @@ static void lguest_load_tls(struct thread_struct *t, unsigned int cpu)
/* There's one problem which normal hardware doesn't have: the Host
* can't handle us removing entries we're currently using. So we clear
* the GS register here: if it's needed it'll be reloaded anyway. */
- loadsegment(gs, 0);
+ lazy_load_gs(0);
lazy_hcall(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu, 0);
}