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Subject[PATCH 20 of 55] x86_64: add workaround for no %gs-based percpu
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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>
---
arch/x86/kernel/head64.c | 11 ++++++++---
arch/x86/xen/enlighten.c | 5 +++++
include/asm-x86/percpu.h | 26 ++++++++++++++++++++++++++
include/asm-x86/setup.h | 1 +
4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -38,6 +38,13 @@
#else
static struct x8664_pda *__cpu_pda[NR_CPUS] __read_mostly;
#endif
+
+void __init x86_64_init_pda(void)
+{
+ _cpu_pda = __cpu_pda;
+ cpu_pda(0) = &_boot_cpu_pda;
+ pda_init(0);
+}

static void __init zap_identity_mappings(void)
{
@@ -102,9 +109,7 @@

early_printk("Kernel alive\n");

- _cpu_pda = __cpu_pda;
- cpu_pda(0) = &_boot_cpu_pda;
- pda_init(0);
+ x86_64_init_pda();

early_printk("Kernel really alive\n");

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -971,6 +971,7 @@

/* xen_vcpu_setup managed to place the vcpu_info within the
percpu area for all cpus, so make use of it */
+#ifdef CONFIG_X86_32
if (have_vcpu_info_placement) {
printk(KERN_INFO "Xen: using vcpu_info placement\n");

@@ -980,6 +981,7 @@
pv_irq_ops.irq_enable = xen_irq_enable_direct;
pv_mmu_ops.read_cr2 = xen_read_cr2_direct;
}
+#endif
}

static unsigned xen_patch(u8 type, u16 clobbers, void *insnbuf,
@@ -1000,10 +1002,12 @@
goto patch_site

switch (type) {
+#ifdef CONFIG_X86_32
SITE(pv_irq_ops, irq_enable);
SITE(pv_irq_ops, irq_disable);
SITE(pv_irq_ops, save_fl);
SITE(pv_irq_ops, restore_fl);
+#endif /* CONFIG_X86_32 */
#undef SITE

patch_site:
@@ -1323,6 +1327,7 @@
#ifdef CONFIG_X86_64
/* Disable until direct per-cpu data access. */
have_vcpu_info_placement = 0;
+ x86_64_init_pda();
#endif

xen_smp_init();
diff --git a/include/asm-x86/percpu.h b/include/asm-x86/percpu.h
--- a/include/asm-x86/percpu.h
+++ b/include/asm-x86/percpu.h
@@ -21,6 +21,32 @@
#include <asm-generic/percpu.h>

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 */

diff --git a/include/asm-x86/setup.h b/include/asm-x86/setup.h
--- a/include/asm-x86/setup.h
+++ b/include/asm-x86/setup.h
@@ -57,6 +57,7 @@
extern unsigned long init_pg_tables_end;

#else
+void __init x86_64_init_pda(void);
void __init x86_64_start_kernel(char *real_mode);
void __init x86_64_start_reservations(char *real_mode_data);




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