Hi Henry,
On 16/05/2024 11:03, Henry Wang wrote:
There are some use cases in which the dom0less domUs need to have
the XEN_DOMCTL_CDF_iommu set at the domain construction time. For
example, the dynamic dtbo feature allows the domain to be assigned
a device that is behind the IOMMU at runtime. For these use cases,
we need to have a way to specify the domain will need the IOMMU
mapping at domain construction time.
Introduce a "passthrough" DT property for Dom0less DomUs following
the same entry as the xl.cfg. Currently only provide two options,
i.e. "enable" and "disable". Set the XEN_DOMCTL_CDF_iommu at domain
construction time based on the property.
Signed-off-by: Henry Wang <xin.wa...@amd.com>
---
v2:
- New patch to replace the original patch in v1:
"[PATCH 03/15] xen/arm: Always enable IOMMU"
---
docs/misc/arm/device-tree/booting.txt | 13 +++++++++++++
xen/arch/arm/dom0less-build.c | 7 +++++--
2 files changed, 18 insertions(+), 2 deletions(-)
diff --git a/docs/misc/arm/device-tree/booting.txt
b/docs/misc/arm/device-tree/booting.txt
index bbd955e9c2..61f9082553 100644
--- a/docs/misc/arm/device-tree/booting.txt
+++ b/docs/misc/arm/device-tree/booting.txt
@@ -260,6 +260,19 @@ with the following properties:
value specified by Xen command line parameter gnttab_max_maptrack_frames
(or its default value if unspecified, i.e. 1024) is used.
+- passthrough
+
+ A string property specifying whether IOMMU mappings are enabled for the
+ domain and hence whether it will be enabled for passthrough hardware.
+ Possible property values are:
+
+ - "enabled"
+ IOMMU mappings are enabled for the domain.
+
+ - "disabled"
+ IOMMU mappings are disabled for the domain and so hardware may not be
+ passed through. This option is the default if this property is missing.
Looking at the code below, it seems like the default will depend on
whether the partial device-tree is present. Did I misunderstand?
+
Under the "xen,domain" compatible node, one or more sub-nodes are present
for the DomU kernel and ramdisk.
diff --git a/xen/arch/arm/dom0less-build.c b/xen/arch/arm/dom0less-build.c
index 74f053c242..1396a102e1 100644
--- a/xen/arch/arm/dom0less-build.c
+++ b/xen/arch/arm/dom0less-build.c
@@ -848,6 +848,7 @@ static int __init construct_domU(struct domain *d,
void __init create_domUs(void)
{
struct dt_device_node *node;
+ const char *dom0less_iommu;
const struct dt_device_node *cpupool_node,
*chosen = dt_find_node_by_path("/chosen");
@@ -895,8 +896,10 @@ 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") &&
- iommu_enabled )
+ if ( iommu_enabled &&
+ ((!dt_property_read_string(node, "passthrough", &dom0less_iommu)
&&
+ !strcmp(dom0less_iommu, "enabled")) ||
+ dt_find_compatible_node(node, NULL, "multiboot,device-tree")) )
This condition is getting a little bit harder to read. Can we cache the
"passthrough" flag separately?
Also, shouldn't we throw a panic if passthrough = "enabled" but the
IOMMU is enabled?
d_cfg.flags |= XEN_DOMCTL_CDF_iommu;
if ( !dt_property_read_u32(node, "nr_spis", &d_cfg.arch.nr_spis) )
Cheers,
--
Julien Grall
