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Re: [PATCH 03/12] xen/arm: introduce 1:1 mapping for domUs
On 15/04/2020 02:02, Stefano Stabellini wrote:
In some cases it is desirable to map domU memory 1:1 (guest physical ==
physical.) For instance, because we want to assign a device to the domU
but the IOMMU is not present or cannot be used. In these cases, other
mechanisms should be used for DMA protection, e.g. a MPU.
I am not against this, however the documentation should clearly explain
that you are making your platform insecure unless you have other mean
for DMA protection.
This patch introduces a new device tree option for dom0less guests to
request a domain to be directly mapped. It also specifies the memory
ranges. This patch documents the new attribute and parses it at boot
time. (However, the implementation of 1:1 mapping is missing and just
BUG() out at the moment.) Finally the patch sets the new direct_map
flag for DomU domains.
Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
---
docs/misc/arm/device-tree/booting.txt | 13 +++++++
docs/misc/arm/passthrough-noiommu.txt | 35 ++++++++++++++++++
xen/arch/arm/domain_build.c | 52 +++++++++++++++++++++++++--
3 files changed, 98 insertions(+), 2 deletions(-)
create mode 100644 docs/misc/arm/passthrough-noiommu.txt
diff --git a/docs/misc/arm/device-tree/booting.txt
b/docs/misc/arm/device-tree/booting.txt
index 5243bc7fd3..fce5f7ed5a 100644
--- a/docs/misc/arm/device-tree/booting.txt
+++ b/docs/misc/arm/device-tree/booting.txt
@@ -159,6 +159,19 @@ with the following properties:
used, or GUEST_VPL011_SPI+1 if vpl011 is enabled, whichever is
greater.
+- direct-map
+
+ Optional. An array of integer pairs specifying addresses and sizes.
+ direct_map requests the memory of the domain to be 1:1 mapped with
+ the memory ranges specified as argument. Only sizes that are a
+ power of two number of pages are allowed.
+
+- #direct-map-addr-cells and #direct-map-size-cells
+
+ The number of cells to use for the addresses and for the sizes in
+ direct-map. Default and maximum are 2 cells for both addresses and
+ sizes.
+
As this is going to be mostly used for passthrough, can't we take
advantage of the partial device-tree and describe the memory region
using memory node?
- #address-cells and #size-cells
Both #address-cells and #size-cells need to be specified because
diff --git a/docs/misc/arm/passthrough-noiommu.txt
b/docs/misc/arm/passthrough-noiommu.txt
new file mode 100644
index 0000000000..d2bfaf26c3
--- /dev/null
+++ b/docs/misc/arm/passthrough-noiommu.txt
@@ -0,0 +1,35 @@
+Request Device Assignment without IOMMU support
+===============================================
+
+Add xen,force-assign-without-iommu; to the device tree snippet
+
+ ethernet: ethernet@ff0e0000 {
+ compatible = "cdns,zynqmp-gem";
+ xen,path = "/amba/ethernet@ff0e0000";
+ xen,reg = <0x0 0xff0e0000 0x1000 0x0 0xff0e0000>;
+ xen,force-assign-without-iommu;
+
+Optionally, if none of the domains require an IOMMU, then it could be
+disabled (not recommended). For instance by adding status = "disabled";
+under the smmu node:
+
+ smmu@fd800000 {
+ compatible = "arm,mmu-500";
+ status = "disabled";
I am not sure why this section is added in this patch. Furthermore, the
file is named "noiommu" but here you mention the IOMMU.
+
+
+Request 1:1 memory mapping for the dom0-less domain
+===================================================
+
+Add a direct-map property under the appropriate /chosen/domU node with
+the memory ranges you want to assign to your domain. If you are using
+imagebuilder, you can add to boot.source something like the following:
+
+ fdt set /chosen/domU0 direct-map <0x0 0x10000000 0x0 0x10000000 0x0
0x60000000 0x0 0x10000000>
+
+Which will assign the ranges:
+
+ 0x10000000 - 0x20000000
+ 0x60000000 - 0x70000000
+
+to the first dom0less domU.
diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 2ec7453aa3..a2bb411568 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -2435,7 +2435,51 @@ static int __init construct_domU(struct domain *d,
/* type must be set before allocate memory */
d->arch.type = kinfo.type;
#endif
- allocate_memory(d, &kinfo);
+
+ if ( !is_domain_direct_mapped(d) )
+ allocate_memory(d, &kinfo);
+ else
+ {
+ struct membank banks[NR_MEM_BANKS];
+ const struct dt_property *prop;
+ u32 direct_map_len, direct_map_addr_len = 2, direct_map_size_len = 2;
+ unsigned int i;
+ __be32 *p;
+
+ prop = dt_find_property(node, "direct-map", &direct_map_len);
+ BUG_ON(!prop);
+
+ dt_property_read_u32(node,
+ "#direct-map-addr-cells",
+ &direct_map_addr_len);
+ dt_property_read_u32(node,
+ "#direct-map-size-cells",
+ &direct_map_size_len);
+ BUG_ON(direct_map_size_len > 2 || direct_map_addr_len > 2);
+
+ for ( i = 0, p = prop->value;
+ i < direct_map_len /
+ (4 * (direct_map_addr_len + direct_map_size_len));
+ i++)
+ {
+ int j;
+
+ banks[i].start = 0;
+ for ( j = 0; j < direct_map_addr_len; j++, p++ )
+ banks[i].start |= __be32_to_cpu(*p) << (32*j);
Please use dt_read_number();
+
+ banks[i].size = 0;
+ for ( j = 0; j < direct_map_size_len; j++, p++ )
+ banks[i].size |= __be32_to_cpu(*p) << (32*j);
+
Same here.
+ printk(XENLOG_DEBUG
+ "direct_map start=%#"PRIpaddr" size=%#"PRIpaddr"\n",
+ banks[i].start, banks[i].size);
+ }
+
+ /* reserve_memory_11(d, &kinfo, &banks[0], i); */
+ BUG();
This can be avoided by re-ordering the patches and folding #6 in this patch.
+ }
rc = prepare_dtb_domU(d, &kinfo);
if ( rc < 0 )
@@ -2455,6 +2499,7 @@ void __init create_domUs(void)
{
struct dt_device_node *node;
const struct dt_device_node *chosen = dt_find_node_by_path("/chosen");
+ u32 direct_map = 0;
BUG_ON(chosen == NULL);
dt_for_each_child_node(chosen, node)
@@ -2476,8 +2521,11 @@ void __init create_domUs(void)
panic("Missing property 'cpus' for domain %s\n",`
dt_node_name(node));
- if ( dt_find_compatible_node(node, NULL, "multiboot,device-tree") )
+ dt_find_property(node, "direct-map", &direct_map);
Please use dt_property_read_bool().
+ if ( dt_find_compatible_node(node, NULL, "multiboot,device-tree") &&
+ !direct_map )
d_cfg.flags |= XEN_DOMCTL_CDF_iommu;
+ flags.arch.is_direct_map = direct_map != 0;
if ( !dt_property_read_u32(node, "nr_spis", &d_cfg.arch.nr_spis) )
{
Cheers,
--
Julien Grall
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