[Xen-devel] [PATCH v2] xen/swiotlb: don't initialize swiotlb twice on arm64

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

From: Stefano Stabellini <stefanos@xxxxxxxxxx>

On arm64 swiotlb is often (not always) already initialized by mem_init.
We don't want to initialize it twice, which would trigger a second
memory allocation. Moreover, the second memory pool is typically made of
high pages and ends up replacing the original memory pool of low pages.
As a side effect of this change, it is possible to have low pages in
swiotlb-xen on arm64.

Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
---
Changes in v2:
- improve commit message
- don't add nested ifs

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 877baf2..8a3cdd1 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -211,6 +211,15 @@ int __ref xen_swiotlb_init(int verbose, bool early)
 retry:
        bytes = xen_set_nslabs(xen_io_tlb_nslabs);
        order = get_order(xen_io_tlb_nslabs << IO_TLB_SHIFT);
+
+       /*
+        * IO TLB memory already allocated. Just use it.
+        */
+       if (io_tlb_start != 0) {
+               xen_io_tlb_start = phys_to_virt(io_tlb_start);
+               goto end;
+       }
+
        /*
         * Get IO TLB memory from any location.
         */
@@ -240,7 +249,6 @@ int __ref xen_swiotlb_init(int verbose, bool early)
                m_ret = XEN_SWIOTLB_ENOMEM;
                goto error;
        }
-       xen_io_tlb_end = xen_io_tlb_start + bytes;
        /*
         * And replace that memory with pages under 4GB.
         */
@@ -267,6 +275,8 @@ int __ref xen_swiotlb_init(int verbose, bool early)
        } else
                rc = swiotlb_late_init_with_tbl(xen_io_tlb_start, 
xen_io_tlb_nslabs);
 
+end:
+       xen_io_tlb_end = xen_io_tlb_start + bytes;
        if (!rc)
                swiotlb_set_max_segment(PAGE_SIZE);
 
-- 
2.7.4


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