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Commit 5b09b287 authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by Ingo Molnar
Browse files

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: default avatarJeremy 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: default avatarIngo Molnar <mingo@elte.hu>
parent a9e7062d

arch/x86/kernel/head64.c

+8 −3
Original line number Diff line number Diff line
@@ -39,6 +39,13 @@ static struct x8664_pda *__cpu_pda[NR_CPUS] __initdata; 
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)

{

	pgd_t *pgd = pgd_offset_k(0UL);
@@ -102,9 +109,7 @@ void __init x86_64_start_kernel(char * real_mode_data) 


	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");

arch/x86/xen/enlighten.c

+5 −0
Original line number Diff line number Diff line
@@ -971,6 +971,7 @@ void xen_setup_vcpu_info_placement(void) 


	/* 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 @@ void xen_setup_vcpu_info_placement(void) 
		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 @@ static unsigned xen_patch(u8 type, u16 clobbers, void *insnbuf, 
	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 @@ asmlinkage void __init xen_start_kernel(void) 
#ifdef CONFIG_X86_64

	/* Disable until direct per-cpu data access. */

	have_vcpu_info_placement = 0;

	x86_64_init_pda();

#endif



	xen_smp_init();

include/asm-x86/percpu.h

+26 −0
Original line number Diff line number Diff line
@@ -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__

include/asm-x86/setup.h

+1 −0
Original line number Diff line number Diff line
@@ -76,6 +76,7 @@ extern unsigned long init_pg_tables_start; 
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);