From 7929eb9cf643ae416e5081b2a6fa558d37b9854c Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Thu, 3 Sep 2009 21:45:59 +0100 Subject: [PATCH] ARM: 5691/1: fix cache aliasing issues between kmap() and kmap_atomic() with highmem Let's suppose a highmem page is kmap'd with kmap(). A pkmap entry is used, the page mapped to it, and the virtual cache is dirtied. Then kunmap() is used which does virtually nothing except for decrementing a usage count. Then, let's suppose the _same_ page gets mapped using kmap_atomic(). It is therefore mapped onto a fixmap entry instead, which has a different virtual address unaware of the dirty cache data for that page sitting in the pkmap mapping. Fortunately it is easy to know if a pkmap mapping still exists for that page and use it directly with kmap_atomic(), thanks to kmap_high_get(). And actual testing with a printk in the added code path shows that this condition is actually met *extremely* frequently. Seems that we've been quite lucky that things have worked so well with highmem so far. Cc: stable@kernel.org Signed-off-by: Nicolas Pitre Signed-off-by: Russell King --- arch/arm/mm/highmem.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c index a34954d9df7..73cae57fa70 100644 --- a/arch/arm/mm/highmem.c +++ b/arch/arm/mm/highmem.c @@ -40,11 +40,16 @@ void *kmap_atomic(struct page *page, enum km_type type) { unsigned int idx; unsigned long vaddr; + void *kmap; pagefault_disable(); if (!PageHighMem(page)) return page_address(page); + kmap = kmap_high_get(page); + if (kmap) + return kmap; + idx = type + KM_TYPE_NR * smp_processor_id(); vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx); #ifdef CONFIG_DEBUG_HIGHMEM @@ -80,6 +85,9 @@ void kunmap_atomic(void *kvaddr, enum km_type type) #else (void) idx; /* to kill a warning */ #endif + } else if (vaddr >= PKMAP_ADDR(0) && vaddr < PKMAP_ADDR(LAST_PKMAP)) { + /* this address was obtained through kmap_high_get() */ + kunmap_high(pte_page(pkmap_page_table[PKMAP_NR(vaddr)])); } pagefault_enable(); } -- 2.39.3