[ARM] Fix ASID version switch
Close a hole in the ASID version switch, particularly the following
scenario:
CPU0 MM PID CPU1 MM PID
idle
A pid(A)
A idle(lazy tlb)
* new asid version triggered by B *
B pid(B)
A pid(A)
* MM A gets new asid version *
A idle(lazy tlb)
A pid(A)
* CPU1 doesn't see the new ASID *
The result is that CPU1 continues running with the hardware set
for the original (stale) ASID value, but mm->context.id contains
the new ASID value. The result is that the next MM fault on CPU1
updates the page table entries, but flush_tlb_page() fails due to
wrong ASID.
There is a related case with a threaded application is allocated
a new ASID on one CPU while another of its threads is running on
some different CPU. This scenario is not fixed by this commit.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/mm/context.c b/arch/arm/mm/context.c
index 9da43a0..930c04c 100644
--- a/arch/arm/mm/context.c
+++ b/arch/arm/mm/context.c
@@ -14,7 +14,8 @@
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
-unsigned int cpu_last_asid = { 1 << ASID_BITS };
+static DEFINE_SPINLOCK(cpu_asid_lock);
+unsigned int cpu_last_asid = ASID_FIRST_VERSION;
/*
* We fork()ed a process, and we need a new context for the child
@@ -31,15 +32,16 @@
{
unsigned int asid;
+ spin_lock(&cpu_asid_lock);
asid = ++cpu_last_asid;
if (asid == 0)
- asid = cpu_last_asid = 1 << ASID_BITS;
+ asid = cpu_last_asid = ASID_FIRST_VERSION;
/*
* If we've used up all our ASIDs, we need
* to start a new version and flush the TLB.
*/
- if ((asid & ~ASID_MASK) == 0) {
+ if (unlikely((asid & ~ASID_MASK) == 0)) {
asid = ++cpu_last_asid;
/* set the reserved ASID before flushing the TLB */
asm("mcr p15, 0, %0, c13, c0, 1 @ set reserved context ID\n"
@@ -48,6 +50,8 @@
isb();
flush_tlb_all();
}
+ spin_unlock(&cpu_asid_lock);
+ mm->cpu_vm_mask = cpumask_of_cpu(smp_processor_id());
mm->context.id = asid;
}