[Xen-devel] [PATCH v5 7/8] xen/arm: introduce nr_spis

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

We don't have a clear way to know how many virtual SPIs we need for the
dom0-less domains. Introduce a new option under xen,domain to specify
the number of SPIs to allocate for a domain.

The property is optional. When absent, we'll use the physical number of
GIC lines for dom0-less domains, just like for dom0.

Remove the old setting of nr_spis based on the presence of the vpl011.

The implication of this change is that without nr_spis dom0less domains
get the same amount of SPI allocated as dom0, regardless of how many
physical devices they have assigned, and regardless of whether they have
a virtual pl011 (which also needs an emulated SPI). For instance, we
could end up exposing 256 SPIs for each dom0less domain without a
nr_spis property. If we have 4 dom0less domains without nr_spis, it
would result in 80K of additional memory being used.

When nr_spis is present, the domain gets exactly nr_spis allocated SPIs.
If the number is too low, it might not be enough for the devices
assigned it to it. If the number is less than GUEST_VPL011_SPI, the
virtual pl011 won't work.

Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
Reviewed-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
---
Changes in v5:
- improve commit message
- allocate enough SPIs for vpl011

Changes in v4:
- improve commit message

Changes in v3:
- improve commit message
- introduce nr_spis
---
 xen/arch/arm/domain_build.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 414893bc24..bf4d960eb5 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -2345,7 +2345,6 @@ void __init create_domUs(void)
         struct domain *d;
         struct xen_domctl_createdomain d_cfg = {
             .arch.gic_version = XEN_DOMCTL_CONFIG_GIC_NATIVE,
-            .arch.nr_spis = 0,
             .flags = XEN_DOMCTL_CDF_hvm | XEN_DOMCTL_CDF_hap |
                      XEN_DOMCTL_CDF_iommu,
             .max_evtchn_port = -1,
@@ -2356,13 +2355,23 @@ void __init create_domUs(void)
         if ( !dt_device_is_compatible(node, "xen,domain") )
             continue;
 
-        if ( dt_property_read_bool(node, "vpl011") )
-            d_cfg.arch.nr_spis = GUEST_VPL011_SPI - 32 + 1;
-
         if ( !dt_property_read_u32(node, "cpus", &d_cfg.max_vcpus) )
             panic("Missing property 'cpus' for domain %s\n",
                   dt_node_name(node));
 
+        if ( !dt_property_read_u32(node, "nr_spis", &d_cfg.arch.nr_spis) )
+        {
+            d_cfg.arch.nr_spis = gic_number_lines() - 32;
+
+            /*
+             * vpl011 uses one emulated SPI. If vpl011 is requested, make
+             * sure that we allocate enough SPIs for it.
+             */
+            if ( dt_property_read_bool(node, "vpl011") )
+                d_cfg.arch.nr_spis = MAX(d_cfg.arch.nr_spis,
+                                         GUEST_VPL011_SPI - 32 + 1);
+        }
+
         d = domain_create(++max_init_domid, &d_cfg, false);
         if ( IS_ERR(d) )
             panic("Error creating domain %s\n", dt_node_name(node));
-- 
2.17.1


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