Messages in this thread | | | Date | Sat, 28 Mar 2009 06:48:53 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH 1/2] x86/mm: maintain a percpu "in get_user_pages_fast" flag |
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Jeremy Fitzhardinge wrote: > get_user_pages_fast() relies on cross-cpu tlb flushes being a barrier > between clearing and setting a pte, and before freeing a pagetable page. > It usually does this by disabling interrupts to hold off IPIs, but > some tlb flush implementations don't use IPIs for tlb flushes, and > must use another mechanism. > > In this change, add in_gup_cpumask, which is a cpumask of cpus currently > performing a get_user_pages_fast traversal of a pagetable. A cross-cpu > tlb flush function can use this to determine whether it should hold-off > on the flush until the gup_fast has finished. > > @@ -255,6 +260,10 @@ int get_user_pages_fast(unsigned long start, int > nr_pages, int write, > * address down to the the page and take a ref on it. > */ > local_irq_disable(); > + > + cpu = smp_processor_id(); > + cpumask_set_cpu(cpu, in_gup_cpumask); > +
This will bounce a cacheline, every time. Please wrap in CONFIG_XEN and skip at runtime if Xen is not enabled.
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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