[Xen-devel] [PATCH v2 2/2] 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.

Lastly, rename vgic_v3_rdist_count to reflect the value return by the
helper.

Reported-by: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx>
Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx>

---
    Changes in v2:
        - Rename vgic_v3_rdist_count to vgic_v3_max_rdist_count
        - Fixup #re-distributors
        - Fix typoes
        - Add Shameer's tested tag
---
 xen/arch/arm/gic-v3.c  | 14 +++++++++++---
 xen/arch/arm/vgic-v3.c | 21 ++++++++++++++++++---
 2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/xen/arch/arm/gic-v3.c b/xen/arch/arm/gic-v3.c
index c98a163ee7..2c1454f425 100644
--- a/xen/arch/arm/gic-v3.c
+++ b/xen/arch/arm/gic-v3.c
@@ -1265,7 +1265,8 @@ static int gicv3_make_hwdom_dt_node(const struct domain 
*d,
     if ( res )
         return res;
 
-    res = fdt_property_cell(fdt, "#redistributor-regions", gicv3.rdist_count);
+    res = fdt_property_cell(fdt, "#redistributor-regions",
+                            d->arch.vgic.nr_regions);
     if ( res )
         return res;
 
@@ -1274,8 +1275,10 @@ 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 use 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 )
@@ -1466,6 +1469,7 @@ static inline bool gic_dist_supports_dvis(void)
 }
 
 static int gicv3_make_hwdom_madt(const struct domain *d, u32 offset)
+
 {
     struct acpi_subtable_header *header;
     struct acpi_madt_generic_interrupt *host_gicc, *gicc;
@@ -1503,7 +1507,11 @@ 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..efe824c6fb 100644
--- a/xen/arch/arm/vgic-v3.c
+++ b/xen/arch/arm/vgic-v3.c
@@ -1640,7 +1640,11 @@ static int vgic_v3_vcpu_init(struct vcpu *v)
     return 0;
 }
 
-static inline unsigned int vgic_v3_rdist_count(struct domain *d)
+/*
+ * Return the maximum number possible of re-distributor regions for
+ * a given domain.
+ */
+static inline unsigned int vgic_v3_max_rdist_count(struct domain *d)
 {
     /*
      * Normally there is only one GICv3 redistributor region.
@@ -1662,7 +1666,7 @@ static int vgic_v3_real_domain_init(struct domain *d)
     int rdist_count, i, ret;
 
     /* Allocate memory for Re-distributor regions */
-    rdist_count = vgic_v3_rdist_count(d);
+    rdist_count = vgic_v3_max_rdist_count(d);
 
     rdist_regions = xzalloc_array(struct vgic_rdist_region, rdist_count);
     if ( !rdist_regions )
@@ -1695,8 +1699,19 @@ 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 use 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
@@ -1825,7 +1840,7 @@ int vgic_v3_init(struct domain *d, int *mmio_count)
     }
 
     /* GICD region + number of Redistributors */
-    *mmio_count = vgic_v3_rdist_count(d) + 1;
+    *mmio_count = vgic_v3_max_rdist_count(d) + 1;
 
     /* one region per ITS */
     *mmio_count += vgic_v3_its_count(d);
-- 
2.11.0


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