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MIPS: Fix machine check exception in kmap_coherent()

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On an SMP system with cache aliases, the following sequence of events may
happen:

1) copy_user_highpage() runs on CPU0, invoking kmap_coherent() to create a
   temporary mapping in the fixmap region
2) copy_page() starts on CPU0
3) CPU1 sends CPU0 an IPI asking CPU0 to run local_r4k_flush_cache_page()
4) CPU0 takes the interrupt, interrupting copy_page()
5) local_r4k_flush_cache_page() on CPU0 calls kmap_coherent() again
6) The second invocation of kmap_coherent() on CPU0 tries to use the
   same fixmap virtual address that was being used by copy_user_highpage()
7) CPU0 throws a machine check exception for the TLB address conflict

Fixed by creating an extra set of fixmap entries for use in interrupt
handlers.  This prevents fixmap VA conflicts between copy_user_highpage()
running in user context, and local_r4k_flush_cache_page() invoked from an
SMP IPI.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Kevin Cernekee 2009-09-07 11:11:31 -07:00 committed by Ralf Baechle
parent 39d2211d20
commit 0f334a3e8c
2 changed files with 7 additions and 3 deletions
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4
arch/mips/include/asm/fixmap.h
View File

@ -48,9 +48,9 @@ enum fixed_addresses {
#define FIX_N_COLOURS 8
FIX_CMAP_BEGIN,
#ifdef CONFIG_MIPS_MT_SMTC
FIX_CMAP_END = FIX_CMAP_BEGIN + (FIX_N_COLOURS * NR_CPUS),
FIX_CMAP_END = FIX_CMAP_BEGIN + (FIX_N_COLOURS * NR_CPUS * 2),
#else
FIX_CMAP_END = FIX_CMAP_BEGIN + FIX_N_COLOURS,
FIX_CMAP_END = FIX_CMAP_BEGIN + (FIX_N_COLOURS * 2),
#endif
#ifdef CONFIG_HIGHMEM
/* reserved pte's for temporary kernel mappings */

6
arch/mips/mm/init.c
View File

@ -27,6 +27,7 @@
#include <linux/swap.h>
#include <linux/proc_fs.h>
#include <linux/pfn.h>
#include <linux/hardirq.h>
#include <asm/asm-offsets.h>
#include <asm/bootinfo.h>
@ -132,7 +133,10 @@ void *kmap_coherent(struct page *page, unsigned long addr)
inc_preempt_count();
idx = (addr >> PAGE_SHIFT) & (FIX_N_COLOURS - 1);
#ifdef CONFIG_MIPS_MT_SMTC
idx += FIX_N_COLOURS * smp_processor_id();
idx += FIX_N_COLOURS * smp_processor_id() +
(in_interrupt() ? (FIX_N_COLOURS * NR_CPUS) : 0);
#else
idx += in_interrupt() ? FIX_N_COLOURS : 0;
#endif
vaddr = __fix_to_virt(FIX_CMAP_END - idx);
pte = mk_pte(page, PAGE_KERNEL);