diff options
| author | Jeremy Fitzhardinge <jeremy@goop.org> | 2008-07-08 15:06:42 -0700 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-07-16 10:58:13 +0200 |
| commit | 5b09b2876ed1a8e34a0da8f069575fc6174e2077 (patch) | |
| tree | 370750e5c1d4073ed4a7525ccd0348e4154ba0d4 /include/asm-x86/percpu.h | |
| parent | a9e7062d7339f1a1df2b6d7e5d595c7d55b56bfb (diff) | |
x86_64: add workaround for no %gs-based percpu
As a stopgap until Mike Travis's x86-64 gs-based percpu patches are
ready, provide workaround functions for x86_read/write_percpu for
Xen's use.
Specifically, this means that we can't really make use of vcpu
placement, because we can't use a single gs-based memory access to get
to vcpu fields. So disable all that for now.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'include/asm-x86/percpu.h')
| -rw-r--r-- | include/asm-x86/percpu.h | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/include/asm-x86/percpu.h b/include/asm-x86/percpu.h index 912a3a17b9d..4e91ee1e37a 100644 --- a/include/asm-x86/percpu.h +++ b/include/asm-x86/percpu.h @@ -22,6 +22,32 @@ DECLARE_PER_CPU(struct x8664_pda, pda); +/* + * These are supposed to be implemented as a single instruction which + * operates on the per-cpu data base segment. x86-64 doesn't have + * that yet, so this is a fairly inefficient workaround for the + * meantime. The single instruction is atomic with respect to + * preemption and interrupts, so we need to explicitly disable + * interrupts here to achieve the same effect. However, because it + * can be used from within interrupt-disable/enable, we can't actually + * disable interrupts; disabling preemption is enough. + */ +#define x86_read_percpu(var) \ + ({ \ + typeof(per_cpu_var(var)) __tmp; \ + preempt_disable(); \ + __tmp = __get_cpu_var(var); \ + preempt_enable(); \ + __tmp; \ + }) + +#define x86_write_percpu(var, val) \ + do { \ + preempt_disable(); \ + __get_cpu_var(var) = (val); \ + preempt_enable(); \ + } while(0) + #else /* CONFIG_X86_64 */ #ifdef __ASSEMBLY__ |