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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 2/2] xen/m2p: use GNTTABOP_unmap_and_replace to reinstate the original mapping
On 22/07/13 19:02, David Vrabel wrote: > On 22/07/13 17:28, Stefano Stabellini wrote: >> GNTTABOP_unmap_grant_ref unmaps a grant and replaces it with a 0 >> mapping instead of reinstating the original mapping. >> Doing so separately would be racy. >> >> To unmap a grant and reinstate the original mapping atomically we use >> GNTTABOP_unmap_and_replace. >> GNTTABOP_unmap_and_replace doesn't work with GNTMAP_contains_pte, so >> don't use it for kmaps. GNTTABOP_unmap_and_replace zeroes the mapping >> passed in new_addr so we have to reinstate it, however that is a >> per-cpu mapping only used for balloon trade pages, so we can be sure that >> it's not going to be accessed while the mapping is not valid. > > This solves the problem of userspace accessing a disk image on an NFS > mount but what would blkback talking to an iSCSI LUN? Will that need > similar fixes to blkback? This series does not need to fix this now though. I have not played much with iSCSI and blkback, but I guess the same issue exists there, the only difference is that we don't perform the grant mappings with GNTMAP_contains_pte, so less modifications are required. Maybe the unmap and reinstate of the trade page address could be placed somewhere more generic, so that I don't have to also code the multicall in blkback? Adding a proper unmap and replace op that reinstates the trade page address to grant-table.c does seem like the more logical option IMHO. (I can do that after this patch is committed). _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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