[Xen-devel] [PATCH v4 2/2] xen/arm: Automatically find a PPI for the DOM0 event channel interrupt

[Julien Grall <julien.grall@xxxxxxxxxx>]

Use the new vgic interface to know which virtual PPI is free and use it
for the event channel code.

At the DOM0 creation time, Xen doesn't know which vIRQ will be free.
All the vIRQ will be reserved when we parse the device tree. So we can
allocate the vIRQ just after the device tree has been parsed.

It's safe to defer the allocation because no vIRQ can be injected as
long as the vCPU is not online.

As the device tree node "hypervisor" containing the description of the
event channel interrupt is created earlier, add a placeholder which will
be fix up once Xen has allocated the PPI.

Also correct the check in arch_domain_create to use is_hardware_domain.

Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

---
    Changes in v4:
        - Add Ian's ack

    Changes in v3:
        - Create placeholder in make_hypervisor_node
        - Introduce a new function evtchn_fixup to allocate the
        interrupt and fixup the device tree
        - Use the newly function vgic_reserve_ppi
        - Typoes

    Changes in v2:
        - Correct the BUG_ON in arch_domain_create
        - Use if (...) BUG() rather than BUG_ON()
---
 xen/arch/arm/domain.c                | 17 +++++++-----
 xen/arch/arm/domain_build.c          | 51 +++++++++++++++++++++++++++++-------
 xen/arch/arm/platform.c              |  7 -----
 xen/arch/arm/platforms/xgene-storm.c |  1 -
 xen/include/asm-arm/platform.h       |  4 ---
 5 files changed, 53 insertions(+), 27 deletions(-)

diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 7a690b2..fdba081 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -542,13 +542,18 @@ int arch_domain_create(struct domain *d, unsigned int 
domcr_flags)
     if ( (rc = domain_vtimer_init(d)) != 0 )
         goto fail;
 
-    if ( d->domain_id )
+    /*
+     * The hardware domain will get a PPI later in
+     * arch/arm/domain_build.c  depending on the
+     * interrupt map of the hardware.
+     */
+    if ( !is_hardware_domain(d) )
+    {
         d->arch.evtchn_irq = GUEST_EVTCHN_PPI;
-    else
-        d->arch.evtchn_irq = platform_dom0_evtchn_ppi();
-
-    if ( !vgic_reserve_virq(d, d->arch.evtchn_irq) )
-        BUG();
+        /* At this stage vgic_reserve_virq should never fail */
+        if ( !vgic_reserve_virq(d, GUEST_EVTCHN_PPI) )
+            BUG();
+    }
 
     /*
      * Virtual UART is only used by linux early printk and decompress code.
diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index c1df1fc..550193e 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -627,16 +627,10 @@ static int make_hypervisor_node(struct domain *d,
         return res;
 
     /*
-     * interrupts is evtchn upcall:
-     *  - Active-low level-sensitive
-     *  - All cpus
-     *
-     * TODO: Handle correctly the cpumask
+     * Placeholder for the event channel interrupt.  The values will be
+     * replaced later.
      */
-    DPRINT("  Event channel interrupt to %u\n", d->arch.evtchn_irq);
-    set_interrupt_ppi(intr, d->arch.evtchn_irq, 0xf,
-                   DT_IRQ_TYPE_LEVEL_LOW);
-
+    set_interrupt_ppi(intr, ~0, 0xf, DT_IRQ_TYPE_INVALID);
     res = fdt_property_interrupts(fdt, &intr, 1);
     if ( res )
         return res;
@@ -1277,6 +1271,43 @@ static void initrd_load(struct kernel_info *kinfo)
     }
 }
 
+static void evtchn_fixup(struct domain *d, struct kernel_info *kinfo)
+{
+    int res, node;
+    gic_interrupt_t intr;
+
+    /*
+     * The allocation of the event channel IRQ has been deferred until
+     * now. At this time, all PPIs used by DOM0 have been registered.
+     */
+    res = vgic_allocate_ppi(d);
+    if ( res < 0 )
+        panic("Unable to allocate a PPI for the event channel interrupt\n");
+
+    d->arch.evtchn_irq = res;
+
+    printk("Allocating PPI %u for event channel interrupt\n",
+           d->arch.evtchn_irq);
+
+    /* Fix up "interrupts" in /hypervisor node */
+    node = fdt_path_offset(kinfo->fdt, "/hypervisor");
+    if ( node < 0 )
+        panic("Cannot find the /hypervisor node");
+
+    /* Interrupt event channel upcall:
+     *  - Active-low level-sensitive
+     *  - All CPUs
+     *
+     *  TODO: Handle properly the cpumask
+     */
+    set_interrupt_ppi(intr, d->arch.evtchn_irq, 0xf,
+                      DT_IRQ_TYPE_LEVEL_LOW);
+    res = fdt_setprop_inplace(kinfo->fdt, node, "interrupts",
+                              &intr, sizeof(intr));
+    if ( res )
+        panic("Cannot fix up \"interrupts\" property of the hypervisor node");
+}
+
 int construct_dom0(struct domain *d)
 {
     struct kernel_info kinfo = {};
@@ -1338,6 +1369,8 @@ int construct_dom0(struct domain *d)
     kernel_load(&kinfo);
     /* initrd_load will fix up the fdt, so call it before dtb_load */
     initrd_load(&kinfo);
+    /* Allocate the event channel IRQ and fix up the device tree */
+    evtchn_fixup(d, &kinfo);
     dtb_load(&kinfo);
 
     /* Now that we are done restore the original p2m and current. */
diff --git a/xen/arch/arm/platform.c b/xen/arch/arm/platform.c
index cb4cda8..d016797 100644
--- a/xen/arch/arm/platform.c
+++ b/xen/arch/arm/platform.c
@@ -160,13 +160,6 @@ bool_t platform_device_is_blacklisted(const struct 
dt_device_node *node)
     return dt_match_node(blacklist, node);
 }
 
-unsigned int platform_dom0_evtchn_ppi(void)
-{
-    if ( platform && platform->dom0_evtchn_ppi )
-        return platform->dom0_evtchn_ppi;
-    return GUEST_EVTCHN_PPI;
-}
-
 void platform_dom0_gnttab(paddr_t *start, paddr_t *size)
 {
     if ( platform && platform->dom0_gnttab_size )
diff --git a/xen/arch/arm/platforms/xgene-storm.c 
b/xen/arch/arm/platforms/xgene-storm.c
index ef3ba63..eee650e 100644
--- a/xen/arch/arm/platforms/xgene-storm.c
+++ b/xen/arch/arm/platforms/xgene-storm.c
@@ -232,7 +232,6 @@ PLATFORM_START(xgene_storm, "APM X-GENE STORM")
     .quirks = xgene_storm_quirks,
     .specific_mapping = xgene_storm_specific_mapping,
 
-    .dom0_evtchn_ppi = 24,
     .dom0_gnttab_start = 0x1f800000,
     .dom0_gnttab_size = 0x20000,
 PLATFORM_END
diff --git a/xen/include/asm-arm/platform.h b/xen/include/asm-arm/platform.h
index eefaca6..4eba37b 100644
--- a/xen/include/asm-arm/platform.h
+++ b/xen/include/asm-arm/platform.h
@@ -38,10 +38,6 @@ struct platform_desc {
      */
     const struct dt_device_match *blacklist_dev;
     /*
-     * The IRQ (PPI) to use to inject event channels to dom0.
-     */
-    unsigned int dom0_evtchn_ppi;
-    /*
      * The location of a region of physical address space which dom0
      * can use for grant table mappings. If size is zero defaults to
      * 0xb0000000-0xb0020000.
-- 
2.1.4


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