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>
139 lines
3.3 KiB
C
139 lines
3.3 KiB
C
#include <linux/highmem.h>
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#include <linux/module.h>
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#include <linux/swap.h> /* for totalram_pages */
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void *kmap(struct page *page)
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{
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might_sleep();
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if (!PageHighMem(page))
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return page_address(page);
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return kmap_high(page);
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}
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EXPORT_SYMBOL(kmap);
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void kunmap(struct page *page)
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{
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if (in_interrupt())
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BUG();
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if (!PageHighMem(page))
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return;
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kunmap_high(page);
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}
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EXPORT_SYMBOL(kunmap);
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/*
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* kmap_atomic/kunmap_atomic is significantly faster than kmap/kunmap because
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* no global lock is needed and because the kmap code must perform a global TLB
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* invalidation when the kmap pool wraps.
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*
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* However when holding an atomic kmap it is not legal to sleep, so atomic
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* kmaps are appropriate for short, tight code paths only.
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*/
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void *kmap_atomic_prot(struct page *page, pgprot_t prot)
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{
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unsigned long vaddr;
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int 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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BUG_ON(!pte_none(*(kmap_pte-idx)));
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set_pte(kmap_pte-idx, mk_pte(page, prot));
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return (void *)vaddr;
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}
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EXPORT_SYMBOL(kmap_atomic_prot);
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void *__kmap_atomic(struct page *page)
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{
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return kmap_atomic_prot(page, kmap_prot);
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}
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EXPORT_SYMBOL(__kmap_atomic);
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/*
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* This is the same as kmap_atomic() but can map memory that doesn't
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* have a struct page associated with it.
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*/
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void *kmap_atomic_pfn(unsigned long pfn)
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{
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return kmap_atomic_prot_pfn(pfn, kmap_prot);
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}
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EXPORT_SYMBOL_GPL(kmap_atomic_pfn);
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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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if (vaddr >= __fix_to_virt(FIX_KMAP_END) &&
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vaddr <= __fix_to_virt(FIX_KMAP_BEGIN)) {
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int idx, type;
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type = kmap_atomic_idx();
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idx = type + KM_TYPE_NR * smp_processor_id();
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#ifdef CONFIG_DEBUG_HIGHMEM
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WARN_ON_ONCE(vaddr != __fix_to_virt(FIX_KMAP_BEGIN + idx));
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#endif
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/*
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* Force other mappings to Oops if they'll try to access this
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* pte without first remap it. Keeping stale mappings around
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* is a bad idea also, in case the page changes cacheability
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* attributes or becomes a protected page in a hypervisor.
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*/
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kpte_clear_flush(kmap_pte-idx, vaddr);
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kmap_atomic_idx_pop();
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}
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#ifdef CONFIG_DEBUG_HIGHMEM
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else {
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BUG_ON(vaddr < PAGE_OFFSET);
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BUG_ON(vaddr >= (unsigned long)high_memory);
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}
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#endif
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pagefault_enable();
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}
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EXPORT_SYMBOL(__kunmap_atomic);
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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 < FIXADDR_START)
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return virt_to_page(ptr);
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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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EXPORT_SYMBOL(kmap_atomic_to_page);
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void __init set_highmem_pages_init(void)
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{
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struct zone *zone;
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int nid;
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for_each_zone(zone) {
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unsigned long zone_start_pfn, zone_end_pfn;
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if (!is_highmem(zone))
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continue;
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zone_start_pfn = zone->zone_start_pfn;
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zone_end_pfn = zone_start_pfn + zone->spanned_pages;
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nid = zone_to_nid(zone);
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printk(KERN_INFO "Initializing %s for node %d (%08lx:%08lx)\n",
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zone->name, nid, zone_start_pfn, zone_end_pfn);
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add_highpages_with_active_regions(nid, zone_start_pfn,
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zone_end_pfn);
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}
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totalram_pages += totalhigh_pages;
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}
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