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[ARM] 4128/1: Architecture compliant TTBR changing sequence

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On newer architectures (ARMv6, ARMv7), the depth of the prefetch and
branch prediction is implementation defined and there is a small risk
of wrong ASID tagging when changing TTBR0 before setting the new
context id. The recommended solution is to set a reserved ASID during
TTBR changing. This patch reserves ASID 0.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Catalin Marinas 2007-02-05 14:47:40 +01:00 committed by Russell King
parent 620879c9e3
commit 9d99df4b10
1 changed files with 10 additions and 2 deletions
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12
arch/arm/mm/context.c
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@ -19,7 +19,8 @@ unsigned int cpu_last_asid = { 1 << ASID_BITS };
/* /*
* We fork()ed a process, and we need a new context for the child * We fork()ed a process, and we need a new context for the child
* to run in. We reserve version 0 for initial tasks so we will * to run in. We reserve version 0 for initial tasks so we will
* always allocate an ASID. * always allocate an ASID. The ASID 0 is reserved for the TTBR
* register changing sequence.
*/ */
void __init_new_context(struct task_struct *tsk, struct mm_struct *mm) void __init_new_context(struct task_struct *tsk, struct mm_struct *mm)
{ {
@ -38,8 +39,15 @@ void __new_context(struct mm_struct *mm)
* If we've used up all our ASIDs, we need * If we've used up all our ASIDs, we need
* to start a new version and flush the TLB. * to start a new version and flush the TLB.
*/ */
if ((asid & ~ASID_MASK) == 0) if ((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"
:
: "r" (0));
isb();
flush_tlb_all(); flush_tlb_all();
}
mm->context.id = asid; mm->context.id = asid;
} }