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[IA64] Fix race in mm-context wrap-around logic.

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The patch below should fix a race which could cause stale TLB entries.
Specifically, when 2 CPUs ended up racing for entrance to
wrap_mmu_context().  The losing CPU would find that by the time it
acquired ctx.lock, mm->context already had a valid value, but then it
failed to (re-)check the delayed TLB flushing logic and hence could
end up using a context number when there were still stale entries in
its TLB.  The fix is to check for delayed TLB flushes only after
mm->context is valid (non-zero).  The patch also makes GCC v4.x
happier by defining a non-volatile variant of mm_context_t called
nv_mm_context_t.

Signed-off-by: David Mosberger-Tang <David.Mosberger@acm.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>
This commit is contained in:
David Mosberger-Tang 2005-07-25 22:23:00 -07:00 committed by Tony Luck
parent 7d69fa6266
commit badea125d7
2 changed files with 36 additions and 24 deletions
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8
include/asm-ia64/mmu.h
View File

@ -2,10 +2,12 @@
#define __MMU_H
/*
* Type for a context number. We declare it volatile to ensure proper ordering when it's
* accessed outside of spinlock'd critical sections (e.g., as done in activate_mm() and
* init_new_context()).
* Type for a context number. We declare it volatile to ensure proper
* ordering when it's accessed outside of spinlock'd critical sections
* (e.g., as done in activate_mm() and init_new_context()).
*/
typedef volatile unsigned long mm_context_t;
typedef unsigned long nv_mm_context_t;
#endif

52
include/asm-ia64/mmu_context.h
View File

@ -55,34 +55,46 @@ static inline void
delayed_tlb_flush (void)
{
extern void local_flush_tlb_all (void);
unsigned long flags;
if (unlikely(__ia64_per_cpu_var(ia64_need_tlb_flush))) {
local_flush_tlb_all();
__ia64_per_cpu_var(ia64_need_tlb_flush) = 0;
spin_lock_irqsave(&ia64_ctx.lock, flags);
{
if (__ia64_per_cpu_var(ia64_need_tlb_flush)) {
local_flush_tlb_all();
__ia64_per_cpu_var(ia64_need_tlb_flush) = 0;
}
}
spin_unlock_irqrestore(&ia64_ctx.lock, flags);
}
}
static inline mm_context_t
static inline nv_mm_context_t
get_mmu_context (struct mm_struct *mm)
{
unsigned long flags;
mm_context_t context = mm->context;
nv_mm_context_t context = mm->context;
if (context)
return context;
spin_lock_irqsave(&ia64_ctx.lock, flags);
{
/* re-check, now that we've got the lock: */
context = mm->context;
if (context == 0) {
cpus_clear(mm->cpu_vm_mask);
if (ia64_ctx.next >= ia64_ctx.limit)
wrap_mmu_context(mm);
mm->context = context = ia64_ctx.next++;
if (unlikely(!context)) {
spin_lock_irqsave(&ia64_ctx.lock, flags);
{
/* re-check, now that we've got the lock: */
context = mm->context;
if (context == 0) {
cpus_clear(mm->cpu_vm_mask);
if (ia64_ctx.next >= ia64_ctx.limit)
wrap_mmu_context(mm);
mm->context = context = ia64_ctx.next++;
}
}
spin_unlock_irqrestore(&ia64_ctx.lock, flags);
}
spin_unlock_irqrestore(&ia64_ctx.lock, flags);
/*
* Ensure we're not starting to use "context" before any old
* uses of it are gone from our TLB.
*/
delayed_tlb_flush();
return context;
}
@ -104,7 +116,7 @@ destroy_context (struct mm_struct *mm)
}
static inline void
reload_context (mm_context_t context)
reload_context (nv_mm_context_t context)
{
unsigned long rid;
unsigned long rid_incr = 0;
@ -138,7 +150,7 @@ reload_context (mm_context_t context)
static inline void
activate_context (struct mm_struct *mm)
{
mm_context_t context;
nv_mm_context_t context;
do {
context = get_mmu_context(mm);
@ -157,8 +169,6 @@ activate_context (struct mm_struct *mm)
static inline void
activate_mm (struct mm_struct *prev, struct mm_struct *next)
{
delayed_tlb_flush();
/*
* We may get interrupts here, but that's OK because interrupt handlers cannot
* touch user-space.