SUNRPC: Fix TCP receive code on archs with flush_dcache_page()

After receiving data into the page cache, we need to call flush_dcache_page()
for the architectures that define it.

Fixes: 277e4ab7 ("SUNRPC: Simplify TCP receive code by switching...")
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: stable@vger.kernel.org # v4.20
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtsock.c

@@ -48,6 +48,7 @@
 #include <net/udp.h>
 #include <net/tcp.h>
 #include <linux/bvec.h>
+#include <linux/highmem.h>
 #include <linux/uio.h>
 
 #include <trace/events/sunrpc.h>
@@ -376,6 +377,26 @@ xs_read_discard(struct socket *sock, struct msghdr *msg, int flags,
 	return sock_recvmsg(sock, msg, flags);
 }
 
+#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
+static void
+xs_flush_bvec(const struct bio_vec *bvec, size_t count, size_t seek)
+{
+	struct bvec_iter bi = {
+		.bi_size = count,
+	};
+	struct bio_vec bv;
+
+	bvec_iter_advance(bvec, &bi, seek & PAGE_MASK);
+	for_each_bvec(bv, bvec, bi, bi)
+		flush_dcache_page(bv.bv_page);
+}
+#else
+static inline void
+xs_flush_bvec(const struct bio_vec *bvec, size_t count, size_t seek)
+{
+}
+#endif
+
 static ssize_t
 xs_read_xdr_buf(struct socket *sock, struct msghdr *msg, int flags,
 		struct xdr_buf *buf, size_t count, size_t seek, size_t *read)
@@ -409,6 +430,7 @@ xs_read_xdr_buf(struct socket *sock, struct msghdr *msg, int flags,
 				seek + buf->page_base);
 		if (ret <= 0)
 			goto sock_err;
+		xs_flush_bvec(buf->bvec, ret, seek + buf->page_base);
 		offset += ret - buf->page_base;
 		if (offset == count || msg->msg_flags & (MSG_EOR|MSG_TRUNC))
 			goto out;