[Xen-devel] [PATCH 2/3] xen/arm: vgic-v3: Don't create empty re-distributor regions

[Julien Grall <julien.grall@xxxxxxx>]

At the moment, Xen is assuming the hardware domain will have the same
number of re-distributor regions as the host. However, as the
number of CPUs or the stride (e.g on GICv4) may be different we end up
exposing regions which does not contain any re-distributors.

When booting, Linux will go through all the re-distributor region to
check whether a property (e.g vPLIs) is available accross all the
re-distributors. This will result to a data abort on empty regions
because there are no underlying re-distributor.

So we need to limit the number of regions exposed to the hardware
domain. The code reworked to only expose the minimun number of regions
required by the hardware domain. It is assumed the regions will be
populated starting from the first one.

Reported-by: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx>
Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
---
 xen/arch/arm/gic-v3.c  | 10 ++++++++--
 xen/arch/arm/vgic-v3.c | 11 +++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/gic-v3.c b/xen/arch/arm/gic-v3.c
index b2ed0f8b55..4a984cfb12 100644
--- a/xen/arch/arm/gic-v3.c
+++ b/xen/arch/arm/gic-v3.c
@@ -1274,8 +1274,10 @@ static int gicv3_make_hwdom_dt_node(const struct domain 
*d,
      * GIC has two memory regions: Distributor + rdist regions
      * CPU interface and virtual cpu interfaces accessesed as System registers
      * So cells are created only for Distributor and rdist regions
+     * The hardware domain may not used all the regions. So only copy
+     * what is necessary.
      */
-    new_len = new_len * (gicv3.rdist_count + 1);
+    new_len = new_len * (d->arch.vgic.nr_regions + 1);
 
     hw_reg = dt_get_property(gic, "reg", &len);
     if ( !hw_reg )
@@ -1503,7 +1505,11 @@ static int gicv3_make_hwdom_madt(const struct domain *d, 
u32 offset)
 
     /* Add Generic Redistributor */
     size = sizeof(struct acpi_madt_generic_redistributor);
-    for ( i = 0; i < gicv3.rdist_count; i++ )
+    /*
+     * The hardware domain may not used all the regions. So only copy
+     * what is necessary.
+     */
+    for ( i = 0; i < d->arch.vgic.nr_regions; i++ )
     {
         gicr = (struct acpi_madt_generic_redistributor *)(base_ptr + 
table_len);
         gicr->header.type = ACPI_MADT_TYPE_GENERIC_REDISTRIBUTOR;
diff --git a/xen/arch/arm/vgic-v3.c b/xen/arch/arm/vgic-v3.c
index df1bab3a35..9f729862da 100644
--- a/xen/arch/arm/vgic-v3.c
+++ b/xen/arch/arm/vgic-v3.c
@@ -1695,8 +1695,19 @@ static int vgic_v3_real_domain_init(struct domain *d)
             d->arch.vgic.rdist_regions[i].first_cpu = first_cpu;
 
             first_cpu += size / GICV3_GICR_SIZE;
+
+            if ( first_cpu >= d->max_vcpus )
+                break;
         }
 
+        /*
+         * The hardware domain may not used all the re-distributors
+         * regions (e.g when the number of vCPUs does not match the
+         * number of pCPUs). Update the number of regions to avoid
+         * exposing unused region as they will not get emulated.
+         */
+        d->arch.vgic.nr_regions = i + 1;
+
         d->arch.vgic.intid_bits = vgic_v3_hw.intid_bits;
     }
     else
-- 
2.11.0


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