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20273941f2
Christoph reported a nice splat which illustrated a race in the new stack based kmap_atomic implementation. The problem is that we pop our stack slot before we're completely done resetting its state -- in particular clearing the PTE (sometimes that's CONFIG_DEBUG_HIGHMEM). If an interrupt happens before we actually clear the PTE used for the last slot, that interrupt can reuse the slot in a dirty state, which triggers a BUG in kmap_atomic(). Fix this by introducing kmap_atomic_idx() which reports the current slot index without actually releasing it and use that to find the PTE and delay the _pop() until after we're completely done. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Reported-by: Christoph Hellwig <hch@infradead.org> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
130 lines
3.1 KiB
C
130 lines
3.1 KiB
C
/*
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* highmem.c: virtual kernel memory mappings for high memory
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*
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* Provides kernel-static versions of atomic kmap functions originally
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* found as inlines in include/asm-sparc/highmem.h. These became
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* needed as kmap_atomic() and kunmap_atomic() started getting
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* called from within modules.
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* -- Tomas Szepe <szepe@pinerecords.com>, September 2002
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*
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* But kmap_atomic() and kunmap_atomic() cannot be inlined in
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* modules because they are loaded with btfixup-ped functions.
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*/
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/*
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* The use of kmap_atomic/kunmap_atomic is discouraged - kmap/kunmap
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* gives a more generic (and caching) interface. But kmap_atomic can
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* be used in IRQ contexts, so in some (very limited) cases we need it.
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*
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* XXX This is an old text. Actually, it's good to use atomic kmaps,
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* provided you remember that they are atomic and not try to sleep
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* with a kmap taken, much like a spinlock. Non-atomic kmaps are
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* shared by CPUs, and so precious, and establishing them requires IPI.
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* Atomic kmaps are lightweight and we may have NCPUS more of them.
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*/
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#include <linux/mm.h>
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#include <linux/highmem.h>
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#include <asm/pgalloc.h>
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#include <asm/cacheflush.h>
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#include <asm/tlbflush.h>
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#include <asm/fixmap.h>
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void *__kmap_atomic(struct page *page)
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{
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unsigned long vaddr;
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long idx, type;
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/* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */
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pagefault_disable();
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if (!PageHighMem(page))
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return page_address(page);
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type = kmap_atomic_idx_push();
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idx = type + KM_TYPE_NR*smp_processor_id();
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vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
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/* XXX Fix - Anton */
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#if 0
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__flush_cache_one(vaddr);
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#else
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flush_cache_all();
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#endif
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#ifdef CONFIG_DEBUG_HIGHMEM
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BUG_ON(!pte_none(*(kmap_pte-idx)));
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#endif
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set_pte(kmap_pte-idx, mk_pte(page, kmap_prot));
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/* XXX Fix - Anton */
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#if 0
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__flush_tlb_one(vaddr);
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#else
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flush_tlb_all();
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#endif
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return (void*) vaddr;
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}
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EXPORT_SYMBOL(__kmap_atomic);
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void __kunmap_atomic(void *kvaddr)
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{
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unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
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int type;
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if (vaddr < FIXADDR_START) { // FIXME
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pagefault_enable();
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return;
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}
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type = kmap_atomic_idx();
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#ifdef CONFIG_DEBUG_HIGHMEM
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{
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unsigned long idx;
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idx = type + KM_TYPE_NR * smp_processor_id();
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BUG_ON(vaddr != __fix_to_virt(FIX_KMAP_BEGIN+idx));
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/* XXX Fix - Anton */
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#if 0
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__flush_cache_one(vaddr);
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#else
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flush_cache_all();
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#endif
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/*
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* force other mappings to Oops if they'll try to access
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* this pte without first remap it
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*/
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pte_clear(&init_mm, vaddr, kmap_pte-idx);
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/* XXX Fix - Anton */
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#if 0
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__flush_tlb_one(vaddr);
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#else
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flush_tlb_all();
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#endif
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}
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#endif
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kmap_atomic_idx_pop();
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pagefault_enable();
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}
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EXPORT_SYMBOL(__kunmap_atomic);
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/* We may be fed a pagetable here by ptep_to_xxx and others. */
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struct page *kmap_atomic_to_page(void *ptr)
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{
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unsigned long idx, vaddr = (unsigned long)ptr;
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pte_t *pte;
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if (vaddr < SRMMU_NOCACHE_VADDR)
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return virt_to_page(ptr);
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if (vaddr < PKMAP_BASE)
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return pfn_to_page(__nocache_pa(vaddr) >> PAGE_SHIFT);
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BUG_ON(vaddr < FIXADDR_START);
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BUG_ON(vaddr > FIXADDR_TOP);
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idx = virt_to_fix(vaddr);
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pte = kmap_pte - (idx - FIX_KMAP_BEGIN);
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return pte_page(*pte);
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}
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