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Date: Sat, 5 Sep 2009 14:38:41 -0700
From: Kevin Cernekee <cernekee@...il.com>
To: ralf@...ux-mips.org
Cc: linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org
Subject: [PATCH] MIPS: Machine check exception in kmap_coherent()
On an SMP MIPS32 2.6.30 system with cache aliases, I am seeing the
following sequence of events:
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
Here is my proposed fix:
a) kmap_coherent() will maintain a flag for each CPU indicating whether
there is an active mapping (kmap_coherent_inuse)
b) kmap_coherent() will return a NULL address in the unlikely case that
it was called while another mapping was already outstanding
c) local_r4k_flush_cache_page() will check for a NULL return value from
kmap_coherent(), and compensate by using indexed cacheops instead of hit
cacheops
Signed-off-by: Kevin Cernekee <cernekee@...il.com>
---
arch/mips/mm/c-r4k.c | 25 +++++++++++++++++++------
arch/mips/mm/init.c | 17 +++++++++++++++--
2 files changed, 34 insertions(+), 8 deletions(-)
diff --git a/arch/mips/mm/c-r4k.c b/arch/mips/mm/c-r4k.c
index 6721ee2..572fe7e 100644
--- a/arch/mips/mm/c-r4k.c
+++ b/arch/mips/mm/c-r4k.c
@@ -459,7 +459,7 @@ static inline void local_r4k_flush_cache_page(void *args)
struct page *page = pfn_to_page(fcp_args->pfn);
int exec = vma->vm_flags & VM_EXEC;
struct mm_struct *mm = vma->vm_mm;
- int map_coherent = 0;
+ int map_coherent = 0, use_indexed = 0;
pgd_t *pgdp;
pud_t *pudp;
pmd_t *pmdp;
@@ -499,13 +499,23 @@ static inline void local_r4k_flush_cache_page(void *args)
vaddr = kmap_coherent(page, addr);
else
vaddr = kmap_atomic(page, KM_USER0);
- addr = (unsigned long)vaddr;
+
+ if (unlikely(vaddr == NULL))
+ use_indexed = 1;
+ else
+ addr = (unsigned long)vaddr;
}
if (cpu_has_dc_aliases || (exec && !cpu_has_ic_fills_f_dc)) {
- r4k_blast_dcache_page(addr);
- if (exec && !cpu_icache_snoops_remote_store)
- r4k_blast_scache_page(addr);
+ if (use_indexed) {
+ r4k_blast_dcache_page_indexed(addr);
+ if (exec && !cpu_icache_snoops_remote_store)
+ r4k_blast_scache_page_indexed(addr);
+ } else {
+ r4k_blast_dcache_page(addr);
+ if (exec && !cpu_icache_snoops_remote_store)
+ r4k_blast_scache_page(addr);
+ }
}
if (exec) {
if (vaddr && cpu_has_vtag_icache && mm == current->active_mm) {
@@ -514,7 +524,10 @@ static inline void local_r4k_flush_cache_page(void *args)
if (cpu_context(cpu, mm) != 0)
drop_mmu_context(mm, cpu);
} else
- r4k_blast_icache_page(addr);
+ if (use_indexed)
+ r4k_blast_icache_page_indexed(addr);
+ else
+ r4k_blast_icache_page(addr);
}
if (vaddr) {
diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
index 0e82050..87967cd 100644
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -31,6 +31,7 @@
#include <asm/asm-offsets.h>
#include <asm/bootinfo.h>
#include <asm/cachectl.h>
+#include <asm/cache.h>
#include <asm/cpu.h>
#include <asm/dma.h>
#include <asm/kmap_types.h>
@@ -105,6 +106,8 @@ unsigned long setup_zero_pages(void)
return 1UL << order;
}
+static int kmap_coherent_inuse[NR_CPUS] ____cacheline_aligned_in_smp;
+
#ifdef CONFIG_MIPS_MT_SMTC
static pte_t *kmap_coherent_pte;
static void __init kmap_coherent_init(void)
@@ -125,14 +128,15 @@ void *kmap_coherent(struct page *page, unsigned long addr)
unsigned long vaddr, flags, entrylo;
unsigned long old_ctx;
pte_t pte;
- int tlbidx;
+ int tlbidx, cpu;
BUG_ON(Page_dcache_dirty(page));
inc_preempt_count();
+ cpu = smp_processor_id();
idx = (addr >> PAGE_SHIFT) & (FIX_N_COLOURS - 1);
#ifdef CONFIG_MIPS_MT_SMTC
- idx += FIX_N_COLOURS * smp_processor_id();
+ idx += FIX_N_COLOURS * cpu;
#endif
vaddr = __fix_to_virt(FIX_CMAP_END - idx);
pte = mk_pte(page, PAGE_KERNEL);
@@ -143,6 +147,13 @@ void *kmap_coherent(struct page *page, unsigned long addr)
#endif
ENTER_CRITICAL(flags);
+ if (unlikely(kmap_coherent_inuse[cpu] != 0)) {
+ vaddr = 0;
+ dec_preempt_count();
+ goto out;
+ }
+ kmap_coherent_inuse[cpu] = 1;
+
old_ctx = read_c0_entryhi();
write_c0_entryhi(vaddr & (PAGE_MASK << 1));
write_c0_entrylo0(entrylo);
@@ -168,6 +179,7 @@ void *kmap_coherent(struct page *page, unsigned long addr)
#endif
tlbw_use_hazard();
write_c0_entryhi(old_ctx);
+out:
EXIT_CRITICAL(flags);
return (void*) vaddr;
@@ -195,6 +207,7 @@ void kunmap_coherent(void)
write_c0_entryhi(old_ctx);
EXIT_CRITICAL(flags);
#endif
+ kmap_coherent_inuse[smp_processor_id()] = 0;
dec_preempt_count();
preempt_check_resched();
}
--
1.6.3.1
--
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