On Tue, 2015-01-06 at 18:57 +0000, David Vrabel wrote: > From: Jenny Herbert <jennifer.herb...@citrix.com> > > Introduce gnttab_unmap_refs_async() that can be used to safely unmap > pages that may be in use (ref count > 1). If the pages are in use the > unmap is deferred and retried later. This polling is not very clever > but it should be good enough if the cases where the delay is necessary > are rare. > > This is needed to allow block backends using grant mapping to safely > use network storage (block or filesystem based such as iSCSI or NFS). > > The network storage driver may complete a block request whilst there > is a queued network packet retry (because the ack from the remote end > races with deciding to queue the retry). The pages for the retried > packet would be grant unmapped and the network driver (or hardware) > would access the unmapped page.
I thought this had been solved a little while ago by mapping a scratch page on unmap even for kernel space grant mappings, but both the design doc and here imply not (i.e. the scratch is for user grant mappings only), so I must be misremembering. Regardless, this approach seems likely to be far better... _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
