Commit 46011e6e authored by David Daney's avatar David Daney Committed by Ralf Baechle

MIPS: Make set_pte() SMP safe.

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: default avatarDavid 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: default avatarRalf Baechle <ralf@linux-mips.org>
parent a4504755
...@@ -182,8 +182,39 @@ static inline void set_pte(pte_t *ptep, pte_t pteval) ...@@ -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, * Make sure the buddy is global too (if it's !none,
* it better already be global) * 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)) if (pte_none(*buddy))
pte_val(*buddy) = pte_val(*buddy) | _PAGE_GLOBAL; pte_val(*buddy) = pte_val(*buddy) | _PAGE_GLOBAL;
#endif /* CONFIG_SMP */
} }
#endif #endif
} }
......
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