[PATCH v6 4/4] xen/arm: vgic: free eSPIs using the bitmap index

[Mykola Kvach <mykola_kvach@xxxxxxxx>]

The allocated_irqs bitmap in the existing vGIC implementation stores eSPI
allocation bits immediately after the regular vIRQ bits.
vgic_reserve_virq() converts an eSPI INTID to this compressed bitmap index,
but vgic_free_virq() used the raw INTID.

Freeing INTID 4096 therefore clears bit 4096 instead of the first eSPI bit.
This writes beyond allocated_irqs and leaves the intended eSPI bit set.
Valid eSPIs reach this path during DOMCTL bind failure cleanup and unbind,
and during vPL011 teardown.

Add virq_to_idx(), the inverse of idx_to_virq(), and use it when reserving
and freeing vIRQs. Use vgic_is_valid_line() for the validity checks when
reserving and freeing vIRQs in both vGIC implementations.

Fixes: bdde400c6e1b ("xen/arm: vgic: add resource management for extended SPIs")
Signed-off-by: Mykola Kvach <mykola_kvach@xxxxxxxx>
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
---
Changes in v5:
- Add the vgic_is_valid_line() guard to vgic_free_virq() in the new
  vGIC implementation and use the same helper in vgic_reserve_virq().

Changes in v4:
- Document the compressed bitmap layout with an ASCII diagram above the
  conversion helpers and refer to struct vgic_dist for the full layout.

Changes in v3:
- Adapt virq_to_idx() to the configuration-neutral is_espi() helper.

Changes in v2:
- Call is_espi() without a configuration guard.
---
 xen/arch/arm/vgic.c      | 42 +++++++++++++++++++++++++++++-----------
 xen/arch/arm/vgic/vgic.c |  5 ++++-
 2 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
index 0ba13e18da..acded6a40f 100644
--- a/xen/arch/arm/vgic.c
+++ b/xen/arch/arm/vgic.c
@@ -25,6 +25,21 @@
 #include <asm/vgic.h>
 
 
+/*
+ * The allocated_irqs bitmap is compressed: eSPI bits immediately follow
+ * regular IRQ bits, skipping the gap in the INTID space.
+ *
+ *   +-----------+-----------+-------------------+-------------------+
+ *   |   SGIs    |   PPIs    |       SPIs        |       eSPIs       |
+ *   +-----------+-----------+-------------------+-------------------+
+ *   0           16          32                  vgic_num_irqs(d)
+ *
+ * INTID ESPI_BASE_INTID maps to bitmap index vgic_num_irqs(d).
+ * The following idx_to_virq() and virq_to_idx() convert between INTIDs
+ * and bitmap indexes.
+ *
+ * See also the allocated_irqs comment in struct vgic_dist.
+ */
 static inline unsigned int idx_to_virq(struct domain *d, unsigned int idx)
 {
     if ( idx >= vgic_num_irqs(d) )
@@ -33,6 +48,16 @@ static inline unsigned int idx_to_virq(struct domain *d, 
unsigned int idx)
     return idx;
 }
 
+static inline unsigned int virq_to_idx(struct domain *d, unsigned int virq)
+{
+    ASSERT(IS_ENABLED(CONFIG_GICV3_ESPI) || !is_espi(virq));
+
+    if ( IS_ENABLED(CONFIG_GICV3_ESPI) && is_espi(virq) )
+        return espi_intid_to_idx(virq) + vgic_num_irqs(d);
+
+    return virq;
+}
+
 bool vgic_is_valid_line(struct domain *d, unsigned int virq)
 {
 #ifdef CONFIG_GICV3_ESPI
@@ -854,19 +879,11 @@ bool vgic_emulate(struct cpu_user_regs *regs, union hsr 
hsr)
 
 bool vgic_reserve_virq(struct domain *d, unsigned int virq)
 {
-    unsigned int idx = virq;
-
     if ( !vgic_is_valid_line(d, virq) )
         return false;
 
-    if ( is_espi(virq) )
-    {
-        unsigned int num_regular_irqs = vgic_num_irqs(d);
-
-        idx = espi_intid_to_idx(virq) + num_regular_irqs;
-    }
-
-    return !test_and_set_bit(idx, d->arch.vgic.allocated_irqs);
+    return !test_and_set_bit(virq_to_idx(d, virq),
+                             d->arch.vgic.allocated_irqs);
 }
 
 int vgic_allocate_virq(struct domain *d, bool spi)
@@ -903,7 +920,10 @@ int vgic_allocate_virq(struct domain *d, bool spi)
 
 void vgic_free_virq(struct domain *d, unsigned int virq)
 {
-    clear_bit(virq, d->arch.vgic.allocated_irqs);
+    if ( !vgic_is_valid_line(d, virq) )
+        return;
+
+    clear_bit(virq_to_idx(d, virq), d->arch.vgic.allocated_irqs);
 }
 
 unsigned int vgic_max_vcpus(unsigned int domctl_vgic_version)
diff --git a/xen/arch/arm/vgic/vgic.c b/xen/arch/arm/vgic/vgic.c
index ba029b8a3b..84212bbefe 100644
--- a/xen/arch/arm/vgic/vgic.c
+++ b/xen/arch/arm/vgic/vgic.c
@@ -712,7 +712,7 @@ bool vgic_evtchn_irq_pending(struct vcpu *v)
 
 bool vgic_reserve_virq(struct domain *d, unsigned int virq)
 {
-    if ( virq >= vgic_num_irqs(d) )
+    if ( !vgic_is_valid_line(d, virq) )
         return false;
 
     return !test_and_set_bit(virq, d->arch.vgic.allocated_irqs);
@@ -756,6 +756,9 @@ int vgic_allocate_virq(struct domain *d, bool spi)
 
 void vgic_free_virq(struct domain *d, unsigned int virq)
 {
+    if ( !vgic_is_valid_line(d, virq) )
+        return;
+
     clear_bit(virq, d->arch.vgic.allocated_irqs);
 }
 
-- 
2.53.0