This is a note to let you know that I have just added a patch titled
MIPS: Make set_pte() SMP safe.
to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree
which can be found at:
http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue
This patch is scheduled to be released in version 3.19.8-ckt7.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
------
>From f3a6cbf273706210c3aea22d29e3c2bf5459e40a Mon Sep 17 00:00:00 2001
From: David Daney <david.daney@xxxxxxxxxx>
Date: Mon, 3 Aug 2015 17:48:43 -0700
Subject: MIPS: Make set_pte() SMP safe.
commit 46011e6ea39235e4aca656673c500eac81a07a17 upstream.
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@xxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Patchwork: https://patchwork.linux-mips.org/patch/10835/
Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
arch/mips/include/asm/pgtable.h | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)
diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
index 845016d..4ec91d5 100644
--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -187,8 +187,39 @@ 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
}
--
1.9.1
