xen/arm: vgic: Ignore write access to ICPENDR*

Currently, Xen will return IO unhandled when guests write ICPENDR*
virtual registers, which will raise a data abort inside the guest.
For Linux guest, these virtual registers will not be accessed. But
for Zephyr, these virtual registers will be accessed during the
initialization. Zephyr guest will get an IO data abort and crash.
Emulating ICPENDR is not easy with the existing vGIC, this patch
reworks the emulation to ignore write access to ICPENDR* virtual
registers and print a message about whether they are already pending
instead of returning unhandled.
More details can be found at [1].

[1] https://github.com/zephyrproject-rtos/zephyr/blob/eaf6cf745df3807e6e
cc941c3a30de6c179ae359/drivers/interrupt_controller/intc_gicv3.c#L274

Signed-off-by: Hongda Deng <hongda.deng@arm.com>
Release-Acked-by: Ian Jackson <iwj@xenproject.org>
Reviewed-by: Julien Grall <jgrall@amazon.com>

xen/arch/arm/vgic-v2.c

@@ -481,10 +481,12 @@ static int vgic_v2_distr_mmio_write(struct vcpu *v, mmio_info_t *info,
 
     case VRANGE32(GICD_ICPENDR, GICD_ICPENDRN):
         if ( dabt.size != DABT_WORD ) goto bad_width;
-        printk(XENLOG_G_ERR
-               "%pv: vGICD: unhandled word write %#"PRIregister" to ICPENDR%d\n",
-               v, r, gicd_reg - GICD_ICPENDR);
-        return 0;
+        rank = vgic_rank_offset(v, 1, gicd_reg - GICD_ICPENDR, DABT_WORD);
+        if ( rank == NULL ) goto write_ignore;
+
+        vgic_check_inflight_irqs_pending(v->domain, v, rank->index, r);
+
+        goto write_ignore;
 
     case VRANGE32(GICD_ISACTIVER, GICD_ISACTIVERN):
         if ( dabt.size != DABT_WORD ) goto bad_width;

xen/arch/arm/vgic-v3.c

@@ -817,10 +817,12 @@ static int __vgic_v3_distr_common_mmio_write(const char *name, struct vcpu *v,
 
     case VRANGE32(GICD_ICPENDR, GICD_ICPENDRN):
         if ( dabt.size != DABT_WORD ) goto bad_width;
-        printk(XENLOG_G_ERR
-               "%pv: %s: unhandled word write %#"PRIregister" to ICPENDR%d\n",
-               v, name, r, reg - GICD_ICPENDR);
-        return 0;
+        rank = vgic_rank_offset(v, 1, reg - GICD_ICPENDR, DABT_WORD);
+        if ( rank == NULL ) goto write_ignore;
+
+        vgic_check_inflight_irqs_pending(v->domain, v, rank->index, r);
+
+        goto write_ignore;
 
     case VRANGE32(GICD_ISACTIVER, GICD_ISACTIVERN):
         if ( dabt.size != DABT_WORD ) goto bad_width;
@@ -986,11 +988,8 @@ static int vgic_v3_rdistr_sgi_mmio_write(struct vcpu *v, mmio_info_t *info,
                                                  info, gicr_reg, r);
 
     case VREG32(GICR_ICPENDR0):
-        if ( dabt.size != DABT_WORD ) goto bad_width;
-        printk(XENLOG_G_ERR
-               "%pv: vGICR: SGI: unhandled word write %#"PRIregister" to ICPENDR0\n",
-               v, r);
-        return 0;
+        return __vgic_v3_distr_common_mmio_write("vGICR: SGI", v,
+                                                 info, gicr_reg, r);
 
     case VREG32(GICR_IGRPMODR0):
         /* We do not implement security extensions for guests, write ignore */

xen/arch/arm/vgic.c

@@ -726,6 +726,34 @@ unsigned int vgic_max_vcpus(unsigned int domctl_vgic_version)
     }
 }
 
+void vgic_check_inflight_irqs_pending(struct domain *d, struct vcpu *v,
+                                      unsigned int rank, uint32_t r)
+{
+    const unsigned long mask = r;
+    unsigned int i;
+
+    for_each_set_bit( i, &mask, 32 )
+    {
+        struct pending_irq *p;
+        struct vcpu *v_target;
+        unsigned long flags;
+        unsigned int irq = i + 32 * rank;
+
+        v_target = vgic_get_target_vcpu(v, irq);
+
+        spin_lock_irqsave(&v_target->arch.vgic.lock, flags);
+
+        p = irq_to_pending(v_target, irq);
+
+        if ( p && !list_empty(&p->inflight) )
+            printk(XENLOG_G_WARNING
+                   "%pv trying to clear pending interrupt %u.\n",
+                   v, irq);
+
+        spin_unlock_irqrestore(&v_target->arch.vgic.lock, flags);
+    }
+}
+
 /*
  * Local variables:
  * mode: C

xen/include/asm-arm/vgic.h

@@ -298,6 +298,8 @@ extern bool vgic_to_sgi(struct vcpu *v, register_t sgir,
                         enum gic_sgi_mode irqmode, int virq,
                         const struct sgi_target *target);
 extern bool vgic_migrate_irq(struct vcpu *old, struct vcpu *new, unsigned int irq);
+extern void vgic_check_inflight_irqs_pending(struct domain *d, struct vcpu *v,
+                                             unsigned int rank, uint32_t r);
 
 #endif /* !CONFIG_NEW_VGIC */