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MIPS: Make set_pte() SMP safe.

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On MIPS the GLOBAL bit of the PTE must have the same value in any
aligned pair of PTEs.  These pairs of PTEs are referred to as
"buddies".  In a SMP system is is possible for two CPUs to be calling
set_pte() on adjacent PTEs at the same time.  There is a race between
setting the PTE and a different CPU setting the GLOBAL bit in its
buddy PTE.

This race can be observed when multiple CPUs are executing
vmap()/vfree() at the same time.

Make setting the buddy PTE's GLOBAL bit an atomic operation to close
the race condition.

The case of CONFIG_64BIT_PHYS_ADDR && CONFIG_CPU_MIPS32 is *not*
handled.

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: <stable@vger.kernel.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10835/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
David Daney 2015-08-03 17:48:43 -07:00 committed by Ralf Baechle
parent a4504755e7
commit 46011e6ea3
1 changed files with 31 additions and 0 deletions
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31
arch/mips/include/asm/pgtable.h
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@ -182,8 +182,39 @@ static inline void set_pte(pte_t *ptep, pte_t pteval)
* Make sure the buddy is global too (if it's !none,
* it better already be global)
*/
#ifdef CONFIG_SMP
/*
* For SMP, multiple CPUs can race, so we need to do
* this atomically.
*/
#ifdef CONFIG_64BIT
#define LL_INSN "lld"
#define SC_INSN "scd"
#else /* CONFIG_32BIT */
#define LL_INSN "ll"
#define SC_INSN "sc"
#endif
unsigned long page_global = _PAGE_GLOBAL;
unsigned long tmp;
__asm__ __volatile__ (
" .set push\n"
" .set noreorder\n"
"1: " LL_INSN " %[tmp], %[buddy]\n"
" bnez %[tmp], 2f\n"
" or %[tmp], %[tmp], %[global]\n"
" " SC_INSN " %[tmp], %[buddy]\n"
" beqz %[tmp], 1b\n"
" nop\n"
"2:\n"
" .set pop"
: [buddy] "+m" (buddy->pte),
[tmp] "=&r" (tmp)
: [global] "r" (page_global));
#else /* !CONFIG_SMP */
if (pte_none(*buddy))
pte_val(*buddy) = pte_val(*buddy) | _PAGE_GLOBAL;
#endif /* CONFIG_SMP */
}
#endif
}