[PATCH v2 3/3] xen/swiotlb: check if the swiotlb has already been initialized

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>

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@xxxxxxxxxx
CC: jgross@xxxxxxxx
Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrvsky@xxxxxxxxxx>
---
Changes in v2:
- use pr_warn
- add reviewed-by
---
 arch/arm/xen/mm.c         | 8 +++++++-
 drivers/xen/swiotlb-xen.c | 5 +++++
 2 files changed, 12 insertions(+), 1 deletion(-)

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;
diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 4c89afc0df62..24d11861ac7d 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -164,6 +164,11 @@ int __ref xen_swiotlb_init(void)
        int rc = -ENOMEM;
        char *start;
 
+       if (io_tlb_default_mem != NULL) {
+               pr_warn("swiotlb buffer already initialized\n");
+               return -EEXIST;
+       }
+
 retry:
        m_ret = XEN_SWIOTLB_ENOMEM;
        order = get_order(bytes);
-- 
2.17.1