NFS/localio: Deal with page bases that are > PAGE_SIZE

When resending requests, etc, the page base can quickly grow larger than
the page size.

Fixes: 091bdcf ("nfs/localio: refactor iocb and iov_iter_bvec initialization")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Reviewed-by: Mike Snitzer <snitzer@kernel.org>

Author: Trond Myklebust

fs/nfs/localio.c

@@ -461,6 +461,8 @@ nfs_local_iters_init(struct nfs_local_kiocb *iocb, int rw)
 	v = 0;
 	total = hdr->args.count;
 	base = hdr->args.pgbase;
+	pagevec += base >> PAGE_SHIFT;
+	base &= ~PAGE_MASK;
 	while (total && v < hdr->page_array.npages) {
 		len = min_t(size_t, total, PAGE_SIZE - base);
 		bvec_set_page(&iocb->bvec[v], *pagevec, len, base);