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x86, mm: Patch out arch_flush_lazy_mmu_mode() when running on bare metal 

Invoking arch_flush_lazy_mmu_mode() results in calls to
preempt_enable()/disable() which may have performance impact.

Since lazy MMU is not used on bare metal we can patch away
arch_flush_lazy_mmu_mode() so that it is never called in such
environment.

[ hpa: the previous patch "Fix vmalloc_fault oops during lazy MMU
  updates" may cause a minor performance regression on
  bare metal.  This patch resolves that performance regression.  It is
  somewhat unclear to me if this is a good -stable candidate. ]

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: http://lkml.kernel.org/r/1364045796-10720-2-git-send-email-konrad.wilk@oracle.com
Tested-by: Josh Boyer <jwboyer@redhat.com>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: <stable@vger.kernel.org> SEE NOTE ABOVE
hifive-unleashed-5.1
Boris Ostrovsky 2013-03-23 09:36:36 -04:00 committed by H. Peter Anvin
parent 1160c2779b
commit 511ba86e1d
5 changed files with 21 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
arch/x86/include/asm/paravirt.h
View File

@ -703,7 +703,10 @@ static inline void arch_leave_lazy_mmu_mode(void)
PVOP_VCALL0(pv_mmu_ops.lazy_mode.leave);
}
void arch_flush_lazy_mmu_mode(void);
static inline void arch_flush_lazy_mmu_mode(void)
{
PVOP_VCALL0(pv_mmu_ops.lazy_mode.flush);
}
static inline void __set_fixmap(unsigned /* enum fixed_addresses */ idx,
phys_addr_t phys, pgprot_t flags)

2
arch/x86/include/asm/paravirt_types.h
View File

@ -91,6 +91,7 @@ struct pv_lazy_ops {
/* Set deferred update mode, used for batching operations. */
void (*enter)(void);
void (*leave)(void);
void (*flush)(void);
};
struct pv_time_ops {
@ -679,6 +680,7 @@ void paravirt_end_context_switch(struct task_struct *next);
void paravirt_enter_lazy_mmu(void);
void paravirt_leave_lazy_mmu(void);
void paravirt_flush_lazy_mmu(void);
void _paravirt_nop(void);
u32 _paravirt_ident_32(u32);

25
arch/x86/kernel/paravirt.c
View File

@ -263,6 +263,18 @@ void paravirt_leave_lazy_mmu(void)
leave_lazy(PARAVIRT_LAZY_MMU);
}
void paravirt_flush_lazy_mmu(void)
{
preempt_disable();
if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_MMU) {
arch_leave_lazy_mmu_mode();
arch_enter_lazy_mmu_mode();
}
preempt_enable();
}
void paravirt_start_context_switch(struct task_struct *prev)
{
BUG_ON(preemptible());
@ -292,18 +304,6 @@ enum paravirt_lazy_mode paravirt_get_lazy_mode(void)
return this_cpu_read(paravirt_lazy_mode);
}
void arch_flush_lazy_mmu_mode(void)
{
preempt_disable();
if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_MMU) {
arch_leave_lazy_mmu_mode();
arch_enter_lazy_mmu_mode();
}
preempt_enable();
}
struct pv_info pv_info = {
.name = "bare hardware",
.paravirt_enabled = 0,
@ -475,6 +475,7 @@ struct pv_mmu_ops pv_mmu_ops = {
.lazy_mode = {
.enter = paravirt_nop,
.leave = paravirt_nop,
.flush = paravirt_nop,
},
.set_fixmap = native_set_fixmap,

1
arch/x86/lguest/boot.c
View File

@ -1334,6 +1334,7 @@ __init void lguest_init(void)
pv_mmu_ops.read_cr3 = lguest_read_cr3;
pv_mmu_ops.lazy_mode.enter = paravirt_enter_lazy_mmu;
pv_mmu_ops.lazy_mode.leave = lguest_leave_lazy_mmu_mode;
pv_mmu_ops.lazy_mode.flush = paravirt_flush_lazy_mmu;
pv_mmu_ops.pte_update = lguest_pte_update;
pv_mmu_ops.pte_update_defer = lguest_pte_update;

1
arch/x86/xen/mmu.c
View File

@ -2196,6 +2196,7 @@ static const struct pv_mmu_ops xen_mmu_ops __initconst = {
.lazy_mode = {
.enter = paravirt_enter_lazy_mmu,
.leave = xen_leave_lazy_mmu,
.flush = paravirt_flush_lazy_mmu,
},
.set_fixmap = xen_set_fixmap,