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authorkaf24@labyrinth.cl.cam.ac.uk <kaf24@labyrinth.cl.cam.ac.uk>2003-03-10 14:42:20 +0000
committerkaf24@labyrinth.cl.cam.ac.uk <kaf24@labyrinth.cl.cam.ac.uk>2003-03-10 14:42:20 +0000
commit0699c3b9e8f3eeec8dea7007d53698c581bba464 (patch)
tree5d5b8c8ec31095e845e5a27640bd636157fe845e /xenolinux-2.4.21-pre4-sparse
parent696f066a077467c05fe73a9efcb4e7db72f81adc (diff)
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bitkeeper revision 1.120 (3e6ca44cvMxdBQkw-MjBh0_JyTebvw)
hypervisor.c: Better synchronisation in page-table update code -- removed locking and replaced with cmpxchg (CAS)
Diffstat (limited to 'xenolinux-2.4.21-pre4-sparse')
-rw-r--r--xenolinux-2.4.21-pre4-sparse/arch/xeno/mm/hypervisor.c176
1 files changed, 97 insertions, 79 deletions
diff --git a/xenolinux-2.4.21-pre4-sparse/arch/xeno/mm/hypervisor.c b/xenolinux-2.4.21-pre4-sparse/arch/xeno/mm/hypervisor.c
index 044c531d35..674d099d6b 100644
--- a/xenolinux-2.4.21-pre4-sparse/arch/xeno/mm/hypervisor.c
+++ b/xenolinux-2.4.21-pre4-sparse/arch/xeno/mm/hypervisor.c
@@ -13,17 +13,26 @@
#include <asm/pgtable.h>
/*
- * This suffices to protect us if we ever move to SMP domains.
- * Further, it protects us against interrupts. At the very least, this is
- * required for the network driver which flushes the update queue before
- * pushing new receive buffers.
+ * A note on atomicity of these operations. We assume that queue_xxx
+ * operations never occur in an asynchronous (eg. interrupt) context.
+ * Therefore they do not need to be synchronised w.r.t. each other.
+ * However, flush_update_queue may be called from an interrupt context
+ * (eg. this is done in the network driver).
+ *
+ * We use lock-free techniques to synchronise on the queue index. If a
+ * queue_xxx operation finds this index changes while it runs, it will
+ * fail and retry.
+ *
+ * Flush operations must synchronize with themselves. They do this by
+ * atomically updating the index to zero on entry. This effectively locks
+ * out any other asynchronous calls to a flush operation.
+ *
+ * Debug routines synchronise by disabling interrupts. It's easier that way.
*/
-static spinlock_t update_lock = SPIN_LOCK_UNLOCKED;
#define QUEUE_SIZE 2048
static page_update_request_t update_queue[QUEUE_SIZE];
-unsigned int pt_update_queue_idx = 0;
-#define idx pt_update_queue_idx
+volatile unsigned int pt_update_queue_idx = 0;
#if PT_UPDATE_DEBUG > 0
page_update_debug_t update_debug_queue[QUEUE_SIZE] = {{0}};
@@ -33,7 +42,11 @@ static void DEBUG_allow_pt_reads(void)
{
pte_t *pte;
page_update_request_t update;
+ unsigned int idx;
+ unsigned long flags;
int i;
+ local_irq_save(flags);
+ idx = pt_update_queue_idx;
for ( i = idx-1; i >= 0; i-- )
{
pte = update_debug_queue[i].ptep;
@@ -43,13 +56,17 @@ static void DEBUG_allow_pt_reads(void)
update.val = update_debug_queue[i].pteval;
HYPERVISOR_pt_update(&update, 1);
}
+ local_irq_restore(flags);
}
static void DEBUG_disallow_pt_read(unsigned long pa)
{
pte_t *pte;
pmd_t *pmd;
pgd_t *pgd;
- unsigned long pteval;
+ unsigned long pteval, flags;
+ unsigned int idx;
+ local_irq_save(flags);
+ idx = pt_update_queue_idx;
/*
* We may fault because of an already outstanding update.
* That's okay -- it'll get fixed up in the fault handler.
@@ -65,6 +82,7 @@ static void DEBUG_disallow_pt_read(unsigned long pa)
HYPERVISOR_pt_update(&update, 1);
update_debug_queue[idx].ptep = pte;
update_debug_queue[idx].pteval = pteval;
+ local_irq_restore(flags);
}
#endif
@@ -87,9 +105,8 @@ unsigned long pt_baseptr;
void _flush_page_update_queue(void)
{
- unsigned long flags;
- spin_lock_irqsave(&update_lock, flags);
- if ( idx == 0 ) goto out;
+ unsigned int idx = xchg(&pt_update_queue_idx, 0);
+ if ( idx == 0 ) return;
#if PT_UPDATE_DEBUG > 1
printk("Flushing %d entries from pt update queue\n", idx);
#endif
@@ -97,111 +114,112 @@ void _flush_page_update_queue(void)
DEBUG_allow_pt_reads();
#endif
HYPERVISOR_pt_update(update_queue, idx);
- idx = 0;
- out:
- spin_unlock_irqrestore(&update_lock, flags);
-}
-
-static void increment_index(void)
-{
- if ( ++idx == QUEUE_SIZE ) _flush_page_update_queue();
}
void queue_l1_entry_update(unsigned long ptr, unsigned long val)
{
- unsigned long flags;
- spin_lock_irqsave(&update_lock, flags);
+ unsigned int idx;
#if PT_UPDATE_DEBUG > 0
DEBUG_disallow_pt_read(ptr);
#endif
- update_queue[idx].ptr = phys_to_machine(ptr);
- update_queue[idx].val = val;
- increment_index();
- spin_unlock_irqrestore(&update_lock, flags);
+ do {
+ idx = pt_update_queue_idx;
+ update_queue[idx].ptr = phys_to_machine(ptr);
+ update_queue[idx].val = val;
+ } while ( cmpxchg(&pt_update_queue_idx, idx, idx+1) != idx );
+ if ( idx == (QUEUE_SIZE-1) ) _flush_page_update_queue();
}
void queue_l2_entry_update(unsigned long ptr, unsigned long val)
{
- unsigned long flags;
- spin_lock_irqsave(&update_lock, flags);
- update_queue[idx].ptr = phys_to_machine(ptr);
- update_queue[idx].val = val;
- increment_index();
- spin_unlock_irqrestore(&update_lock, flags);
+ unsigned int idx;
+ do {
+ idx = pt_update_queue_idx;
+ update_queue[idx].ptr = phys_to_machine(ptr);
+ update_queue[idx].val = val;
+ } while ( cmpxchg(&pt_update_queue_idx, idx, idx+1) != idx );
+ if ( idx == (QUEUE_SIZE-1) ) _flush_page_update_queue();
}
void queue_pt_switch(unsigned long ptr)
{
- unsigned long flags;
- spin_lock_irqsave(&update_lock, flags);
- update_queue[idx].ptr = phys_to_machine(ptr);
- update_queue[idx].ptr |= PGREQ_EXTENDED_COMMAND;
- update_queue[idx].val = PGEXT_NEW_BASEPTR;
- increment_index();
- spin_unlock_irqrestore(&update_lock, flags);
+ unsigned int idx;
+ do {
+ idx = pt_update_queue_idx;
+ update_queue[idx].ptr = phys_to_machine(ptr);
+ update_queue[idx].ptr |= PGREQ_EXTENDED_COMMAND;
+ update_queue[idx].val = PGEXT_NEW_BASEPTR;
+ } while ( cmpxchg(&pt_update_queue_idx, idx, idx+1) != idx );
+ if ( idx == (QUEUE_SIZE-1) ) _flush_page_update_queue();
}
void queue_tlb_flush(void)
{
- unsigned long flags;
- spin_lock_irqsave(&update_lock, flags);
- update_queue[idx].ptr = PGREQ_EXTENDED_COMMAND;
- update_queue[idx].val = PGEXT_TLB_FLUSH;
- increment_index();
- spin_unlock_irqrestore(&update_lock, flags);
+ unsigned int idx;
+ do {
+ idx = pt_update_queue_idx;
+ update_queue[idx].ptr = PGREQ_EXTENDED_COMMAND;
+ update_queue[idx].val = PGEXT_TLB_FLUSH;
+ } while ( cmpxchg(&pt_update_queue_idx, idx, idx+1) != idx );
+ if ( idx == (QUEUE_SIZE-1) ) _flush_page_update_queue();
}
void queue_invlpg(unsigned long ptr)
{
- unsigned long flags;
- spin_lock_irqsave(&update_lock, flags);
- update_queue[idx].ptr = PGREQ_EXTENDED_COMMAND;
- update_queue[idx].val = ptr & PAGE_MASK;
- update_queue[idx].val |= PGEXT_INVLPG;
- increment_index();
- spin_unlock_irqrestore(&update_lock, flags);
+ unsigned int idx;
+ do {
+ idx = pt_update_queue_idx;
+ update_queue[idx].ptr = PGREQ_EXTENDED_COMMAND;
+ update_queue[idx].val = ptr & PAGE_MASK;
+ update_queue[idx].val |= PGEXT_INVLPG;
+ } while ( cmpxchg(&pt_update_queue_idx, idx, idx+1) != idx );
+ if ( idx == (QUEUE_SIZE-1) ) _flush_page_update_queue();
}
void queue_pgd_pin(unsigned long ptr)
{
- unsigned long flags;
- spin_lock_irqsave(&update_lock, flags);
- update_queue[idx].ptr = phys_to_machine(ptr);
- update_queue[idx].ptr |= PGREQ_EXTENDED_COMMAND;
- update_queue[idx].val = PGEXT_PIN_L2_TABLE;
- increment_index();
- spin_unlock_irqrestore(&update_lock, flags);
+ unsigned int idx;
+ do {
+ idx = pt_update_queue_idx;
+ update_queue[idx].ptr = phys_to_machine(ptr);
+ update_queue[idx].ptr |= PGREQ_EXTENDED_COMMAND;
+ update_queue[idx].val = PGEXT_PIN_L2_TABLE;
+ } while ( cmpxchg(&pt_update_queue_idx, idx, idx+1) != idx );
+ if ( idx == (QUEUE_SIZE-1) ) _flush_page_update_queue();
}
void queue_pgd_unpin(unsigned long ptr)
{
- unsigned long flags;
- spin_lock_irqsave(&update_lock, flags);
- update_queue[idx].ptr = phys_to_machine(ptr);
- update_queue[idx].ptr |= PGREQ_EXTENDED_COMMAND;
- update_queue[idx].val = PGEXT_UNPIN_TABLE;
- increment_index();
- spin_unlock_irqrestore(&update_lock, flags);
+ unsigned int idx;
+ do {
+ idx = pt_update_queue_idx;
+ update_queue[idx].ptr = phys_to_machine(ptr);
+ update_queue[idx].ptr |= PGREQ_EXTENDED_COMMAND;
+ update_queue[idx].val = PGEXT_UNPIN_TABLE;
+ } while ( cmpxchg(&pt_update_queue_idx, idx, idx+1) != idx );
+ if ( idx == (QUEUE_SIZE-1) ) _flush_page_update_queue();
}
void queue_pte_pin(unsigned long ptr)
{
- unsigned long flags;
- spin_lock_irqsave(&update_lock, flags);
- update_queue[idx].ptr = phys_to_machine(ptr);
- update_queue[idx].ptr |= PGREQ_EXTENDED_COMMAND;
- update_queue[idx].val = PGEXT_PIN_L1_TABLE;
- increment_index();
- spin_unlock_irqrestore(&update_lock, flags);
+ unsigned int idx;
+ do {
+ idx = pt_update_queue_idx;
+ update_queue[idx].ptr = phys_to_machine(ptr);
+ update_queue[idx].ptr |= PGREQ_EXTENDED_COMMAND;
+ update_queue[idx].val = PGEXT_PIN_L1_TABLE;
+ } while ( cmpxchg(&pt_update_queue_idx, idx, idx+1) != idx );
+ if ( idx == (QUEUE_SIZE-1) ) _flush_page_update_queue();
}
void queue_pte_unpin(unsigned long ptr)
{
- unsigned long flags;
- spin_lock_irqsave(&update_lock, flags);
- update_queue[idx].ptr = phys_to_machine(ptr);
- update_queue[idx].ptr |= PGREQ_EXTENDED_COMMAND;
- update_queue[idx].val = PGEXT_UNPIN_TABLE;
- increment_index();
- spin_unlock_irqrestore(&update_lock, flags);
+ unsigned int idx;
+ do {
+ idx = pt_update_queue_idx;
+ update_queue[idx].ptr = phys_to_machine(ptr);
+ update_queue[idx].ptr |= PGREQ_EXTENDED_COMMAND;
+ update_queue[idx].val = PGEXT_UNPIN_TABLE;
+ } while ( cmpxchg(&pt_update_queue_idx, idx, idx+1) != idx );
+ if ( idx == (QUEUE_SIZE-1) ) _flush_page_update_queue();
}