PPC get_user workaround

Linux 5.12 PPC 5.12 get_user() and __copy_from_user_inatomic()
inline helpers very indirectly include a reference to the GPL'd
array mmu_feature_keys[] and fails to build. Workaround this by
using copy_from_user() and throwing EFAULT for any calls to
__copy_from_user_inatomic(). This is a workaround until a fix
for Linux commit 7613f5a66becfd0e43a0f34de8518695888f5458
"powerpc/64s/kuap: Use mmu_has_feature()" is fully addressed.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Authored-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: szubersk <szuberskidamian@gmail.com>
Closes #11958
Closes #12590
Closes #13367

module/os/linux/zfs/zfs_uio.c

@@ -75,6 +75,7 @@ zfs_uiomove_iov(void *p, size_t n, zfs_uio_rw_t rw, zfs_uio_t *uio)
 			} else {
 				unsigned long b_left = 0;
 				if (uio->uio_fault_disable) {
+#if defined(HAVE___COPY_FROM_USER_INATOMIC)
 					if (!zfs_access_ok(VERIFY_READ,
 					    (iov->iov_base + skip), cnt)) {
 						return (EFAULT);
@@ -84,6 +85,9 @@ zfs_uiomove_iov(void *p, size_t n, zfs_uio_rw_t rw, zfs_uio_t *uio)
 					    __copy_from_user_inatomic(p,
 					    (iov->iov_base + skip), cnt);
 					pagefault_enable();
+#else
+					return (EFAULT);
+#endif
 				} else {
 					b_left =
 					    copy_from_user(p,
@@ -248,7 +252,7 @@ zfs_uio_prefaultpages(ssize_t n, zfs_uio_t *uio)
 			/* touch each page in this segment. */
 			p = iov->iov_base + skip;
 			while (cnt) {
-				if (get_user(tmp, (uint8_t *)p))
+				if (copy_from_user(&tmp, p, 1))
 					return (EFAULT);
 				ulong_t incr = MIN(cnt, PAGESIZE);
 				p += incr;
@@ -256,7 +260,7 @@ zfs_uio_prefaultpages(ssize_t n, zfs_uio_t *uio)
 			}
 			/* touch the last byte in case it straddles a page. */
 			p--;
-			if (get_user(tmp, (uint8_t *)p))
+			if (copy_from_user(&tmp, p, 1))
 				return (EFAULT);
 		}
 	}