KVM does not virtualize low address bits for memory accesses, so we must
require that PCI BAR size is a multiple of 4K for passthrough to work
(this also guarantees that address is 4K aligned).
Users of recent linux kernels can force resource size up to 4K
using:
commit 32a9a682bef2f6fce7026bd94d1ce20028b0e52d
Author: Yuji Shimada <shimada-yxb@xxxxxxxxxxxxxxx>
Date: Mon Mar 16 17:13:39 2009 +0900
PCI: allow assignment of memory resources with a specified alignment
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
diff --git a/hw/device-assignment.c b/hw/device-assignment.c
index 237060f..c2ef31f 100644
--- a/hw/device-assignment.c
+++ b/hw/device-assignment.c
@@ -381,6 +381,14 @@ static int assigned_dev_register_regions(PCIRegion *io_regions,
int t = cur_region->type & IORESOURCE_PREFETCH
? PCI_ADDRESS_SPACE_MEM_PREFETCH
: PCI_ADDRESS_SPACE_MEM;
+ if (cur_region->size & 0xFFF) {
+ fprintf(stderr, "Unable to assign device: PCI region %d "
+ "at address 0x%llx has size 0x%x, "
+ " which is not a multiple of 4K\n",
+ i, (unsigned long long)cur_region->base_addr,
+ cur_region->size);
+ return -1;
+ }
/* map physical memory */
pci_dev->v_addrs[i].e_physbase = cur_region->base_addr;
--
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