xen: Add __GFP_DMA flag when xen_swiotlb_init gets free pages on ARM

Make sure that xen_swiotlb_init allocates buffers that are DMA capable
when at least one memblock is available below 4G. Otherwise we assume
that all devices on the SoC can cope with >4G addresses. We do this on
ARM and ARM64, where dom0 is mapped 1:1, so pfn == mfn in this case.

No functional changes on x86.

From: Chen Baozi <baozich@gmail.com>

Signed-off-by: Chen Baozi <baozich@gmail.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Tested-by: Chen Baozi <baozich@gmail.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
index 793551d15f1d..498325074a06 100644
--- a/arch/arm/xen/mm.c
+++ b/arch/arm/xen/mm.c
@@ -4,6 +4,7 @@
 #include <linux/gfp.h>
 #include <linux/highmem.h>
 #include <linux/export.h>
+#include <linux/memblock.h>
 #include <linux/of_address.h>
 #include <linux/slab.h>
 #include <linux/types.h>
@@ -21,6 +22,20 @@
 #include <asm/xen/hypercall.h>
 #include <asm/xen/interface.h>
 
+unsigned long xen_get_swiotlb_free_pages(unsigned int order)
+{
+        struct memblock_region *reg;
+        gfp_t flags = __GFP_NOWARN;
+
+        for_each_memblock(memory, reg) {
+                if (reg->base < (phys_addr_t)0xffffffff) {
+                        flags |= __GFP_DMA;
+                        break;
+                }
+        }
+        return __get_free_pages(flags, order);
+}
+
 enum dma_cache_op {
        DMA_UNMAP,
        DMA_MAP,