Messages in this thread | | | Date | Tue, 16 Sep 2014 15:51:52 +0200 | From | Paolo Bonzini <> | Subject | Re: [PATCH] kvm: Faults which trigger IO release the mmap_sem |
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Il 15/09/2014 22:11, Andres Lagar-Cavilla ha scritto: > + if (!locked) { > + BUG_ON(npages != -EBUSY);
VM_BUG_ON perhaps?
> @@ -1177,9 +1210,15 @@ static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault, > npages = get_user_page_nowait(current, current->mm, > addr, write_fault, page); > up_read(¤t->mm->mmap_sem); > - } else > - npages = get_user_pages_fast(addr, 1, write_fault, > - page); > + } else { > + /* > + * By now we have tried gup_fast, and possible async_pf, and we > + * are certainly not atomic. Time to retry the gup, allowing > + * mmap semaphore to be relinquished in the case of IO. > + */ > + npages = kvm_get_user_page_retry(current, current->mm, addr, > + write_fault, page);
This is a separate logical change. Was this:
down_read(&mm->mmap_sem); npages = get_user_pages(NULL, mm, addr, 1, 1, 0, NULL, NULL); up_read(&mm->mmap_sem);
the intention rather than get_user_pages_fast?
I think a first patch should introduce kvm_get_user_page_retry ("Retry a fault after a gup with FOLL_NOWAIT.") and the second would add FOLL_TRIED ("This properly relinquishes mmap semaphore if the filemap/swap has to wait on page lock (and retries the gup to completion after that").
Apart from this, the patch looks good. The mm/ parts are minimal, so I think it's best to merge it through the KVM tree with someone's Acked-by.
Paolo
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