xen/swiotlb: check if the swiotlb has already been initialized

xen_swiotlb_init calls swiotlb_late_init_with_tbl, which fails with
-ENOMEM if the swiotlb has already been initialized.

Add an explicit check io_tlb_default_mem != NULL at the beginning of
xen_swiotlb_init. If the swiotlb is already initialized print a warning
and return -EEXIST.

On x86, the error propagates.

On ARM, we don't actually need a special swiotlb buffer (yet), any
buffer would do. So ignore the error and continue.

CC: boris.ostrovsky@oracle.com
CC: jgross@suse.com
Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
Reviewed-by: Boris Ostrovsky <boris.ostrvsky@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210512201823.1963-3-sstabellini@kernel.org
Signed-off-by: Juergen Gross <jgross@suse.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
index 223b1151fd7d..a7e54a087b80 100644
--- a/arch/arm/xen/mm.c
+++ b/arch/arm/xen/mm.c
@@ -138,9 +138,15 @@ void xen_destroy_contiguous_region(phys_addr_t pstart, unsigned int order)
 static int __init xen_mm_init(void)
 {
 	struct gnttab_cache_flush cflush;
+	int rc;
+
 	if (!xen_swiotlb_detect())
 		return 0;
-	xen_swiotlb_init();
+
+	rc = xen_swiotlb_init();
+	/* we can work with the default swiotlb */
+	if (rc < 0 && rc != -EEXIST)
+		return rc;
 
 	cflush.op = 0;
 	cflush.a.dev_bus_addr = 0;