Commit f4b2f07b authored by Konrad Rzeszutek Wilk's avatar Konrad Rzeszutek Wilk
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xen-swiotlb: Retry up three times to allocate Xen-SWIOTLB

We can fail seting up Xen-SWIOTLB if:
 - The host does not have enough contiguous DMA32 memory available
   (can happen on a machine that has fragmented memory from starting,
   stopping many guests).
 - Not enough low memory (almost never happens).

We retry allocating and exchanging the swath of contiguous memory
up to three times. Each time we decrease the amount we need  - the
minimum being of 2MB.

If we compleltly fail, we will print the reason for failure on the Xen
console on top of doing it to earlyprintk=xen console.
Signed-off-by: default avatarKonrad Rzeszutek Wilk <>
parent 917e3e65
......@@ -38,6 +38,7 @@
#include <xen/swiotlb-xen.h>
#include <xen/page.h>
#include <xen/xen-ops.h>
#include <xen/hvc-console.h>
* Used to do a quick range check in swiotlb_tbl_unmap_single and
* swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
......@@ -146,8 +147,10 @@ xen_swiotlb_fixup(void *buf, size_t size, unsigned long nslabs)
void __init xen_swiotlb_init(int verbose)
unsigned long bytes;
int rc;
int rc = -ENOMEM;
unsigned long nr_tbl;
char *m = NULL;
unsigned int repeat = 3;
nr_tbl = swioltb_nr_tbl();
if (nr_tbl)
......@@ -156,16 +159,17 @@ void __init xen_swiotlb_init(int verbose)
xen_io_tlb_nslabs = (64 * 1024 * 1024 >> IO_TLB_SHIFT);
xen_io_tlb_nslabs = ALIGN(xen_io_tlb_nslabs, IO_TLB_SEGSIZE);
bytes = xen_io_tlb_nslabs << IO_TLB_SHIFT;
* Get IO TLB memory from any location.
xen_io_tlb_start = alloc_bootmem(bytes);
if (!xen_io_tlb_start)
panic("Cannot allocate SWIOTLB buffer");
if (!xen_io_tlb_start) {
m = "Cannot allocate Xen-SWIOTLB buffer!\n";
goto error;
xen_io_tlb_end = xen_io_tlb_start + bytes;
* And replace that memory with pages under 4GB.
......@@ -173,17 +177,28 @@ void __init xen_swiotlb_init(int verbose)
rc = xen_swiotlb_fixup(xen_io_tlb_start,
if (rc)
if (rc) {
free_bootmem(__pa(xen_io_tlb_start), bytes);
m = "Failed to get contiguous memory for DMA from Xen!\n"\
"You either: don't have the permissions, do not have"\
" enough free memory under 4GB, or the hypervisor memory"\
"is too fragmented!";
goto error;
start_dma_addr = xen_virt_to_bus(xen_io_tlb_start);
swiotlb_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs, verbose);
panic("DMA(%d): Failed to exchange pages allocated for DMA with Xen! "\
"We either don't have the permission or you do not have enough"\
"free memory under 4GB!\n", rc);
if (repeat--) {
xen_io_tlb_nslabs = max(1024UL, /* Min is 2MB */
(xen_io_tlb_nslabs >> 1));
printk(KERN_INFO "Xen-SWIOTLB: Lowering to %luMB\n",
(xen_io_tlb_nslabs << IO_TLB_SHIFT) >> 20);
goto retry;
xen_raw_printk("%s (rc:%d)", rc, m);
panic("%s (rc:%d)", rc, m);
void *
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