[PATCH v6 2/4] xen/arm: make is_espi() a pure range predicate

[Mykola Kvach <mykola_kvach@xxxxxxxx>]

is_espi() currently changes its result according to CONFIG_GICV3_ESPI.
Without eSPI support, it returns false, and its assertion fails if
an eSPI INTID is passed. Callers therefore use it both to identify
eSPIs and to exclude eSPI handling when support is disabled.

Make is_espi() report only whether an INTID is in the architectural
eSPI range. Check for eSPI support at the call sites.

Use BUG_ON() if the GIC reports an eSPI without compiled-in support,
matching the handling of unsupported LPIs. Treat virtual eSPI lookup
without support as unreachable, with a NULL return from the
espi_to_pending() stub.

Signed-off-by: Mykola Kvach <mykola_kvach@xxxxxxxx>
Reviewed-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
---
Changes in v5:
- Explain why an eSPI cannot be handled without compiled-in support.
- Make both espi_to_pending() helpers static inline and constify d.
- Add ASSERT_UNREACHABLE() to the espi_to_pending() stub.
- Preserve the unmapped LPI comment and clarify that an eSPI lookup
  without support must not occur.

Changes in v4:
- Clarify the existing is_espi() behavior in the commit message.
- Drop the unrelated blank-line removal in vgic.c.
- Use BUG_ON() if the GIC reports an eSPI without eSPI support.
- Drop the redundant CONFIG_GICV3_ESPI check in IRQ dispatch.
- Return NULL for virtual eSPI lookup when eSPI support is disabled.

Changes in v3:
- New preparatory cleanup requested during review.
---
 xen/arch/arm/gic.c             |  6 ++++++
 xen/arch/arm/include/asm/irq.h | 11 -----------
 xen/arch/arm/vgic.c            | 30 ++++++++++++++++++------------
 3 files changed, 24 insertions(+), 23 deletions(-)

diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
index 6a132c64e1..0e96def2d0 100644
--- a/xen/arch/arm/gic.c
+++ b/xen/arch/arm/gic.c
@@ -353,6 +353,12 @@ void gic_interrupt(struct cpu_user_regs *regs, int is_fiq)
         /* Reading IRQ will ACK it */
         irq = gic_hw_ops->read_irq();
 
+        /*
+         * Without CONFIG_GICV3_ESPI, there is no IRQ descriptor or
+         * pending_irq storage for eSPIs, so we cannot handle them.
+         */
+        BUG_ON(!IS_ENABLED(CONFIG_GICV3_ESPI) && is_espi(irq));
+
         if ( likely(irq >= GIC_SGI_STATIC_MAX && irq < 1020) || is_espi(irq) )
         {
             isb();
diff --git a/xen/arch/arm/include/asm/irq.h b/xen/arch/arm/include/asm/irq.h
index 09788dbfeb..c29f3d04a3 100644
--- a/xen/arch/arm/include/asm/irq.h
+++ b/xen/arch/arm/include/asm/irq.h
@@ -66,18 +66,7 @@ static inline bool is_lpi(unsigned int irq)
 
 static inline bool is_espi(unsigned int irq)
 {
-#ifdef CONFIG_GICV3_ESPI
     return irq >= ESPI_BASE_INTID && irq <= ESPI_MAX_INTID;
-#else
-    /*
-     * The function should not be called for eSPIs when CONFIG_GICV3_ESPI is
-     * disabled. Returning false allows the compiler to optimize the code
-     * when the config is disabled, while the assert ensures that out-of-range
-     * array resources are not accessed.
-     */
-    ASSERT(!(irq >= ESPI_BASE_INTID && irq <= ESPI_MAX_INTID));
-    return false;
-#endif
 }
 
 static inline unsigned int espi_intid_to_idx(unsigned int intid)
diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
index e5aca17dcb..0ba13e18da 100644
--- a/xen/arch/arm/vgic.c
+++ b/xen/arch/arm/vgic.c
@@ -62,6 +62,14 @@ static inline struct vgic_irq_rank 
*vgic_get_espi_rank(struct vcpu *v,
     return &v->domain->arch.vgic.ext_shared_irqs[EXT_RANK_NUM2IDX(rank)];
 }
 
+static inline struct pending_irq *espi_to_pending(const struct domain *d,
+                                                  unsigned int irq)
+{
+    unsigned int idx = espi_intid_to_idx(irq) + d->arch.vgic.nr_spis;
+
+    return &d->arch.vgic.pending_irqs[idx];
+}
+
 #else
 static inline bool is_valid_espi_rank(struct domain *d, unsigned int rank)
 {
@@ -78,6 +86,13 @@ static inline struct vgic_irq_rank 
*vgic_get_espi_rank(struct vcpu *v,
     ASSERT_UNREACHABLE();
     return NULL;
 }
+
+static inline struct pending_irq *espi_to_pending(const struct domain *d,
+                                                  unsigned int irq)
+{
+    ASSERT_UNREACHABLE();
+    return NULL;
+}
 #endif
 
 static inline struct vgic_irq_rank *vgic_get_rank(struct vcpu *v,
@@ -698,6 +713,7 @@ bool vgic_to_sgi(struct vcpu *v, register_t sgir, enum 
gic_sgi_mode irqmode,
  * interrupt.
  * This can return NULL if called for an LPI which has been unmapped
  * meanwhile.
+ * This must not be called for an eSPI when CONFIG_GICV3_ESPI is disabled.
  */
 struct pending_irq *irq_to_pending(struct vcpu *v, unsigned int irq)
 {
@@ -715,22 +731,12 @@ struct pending_irq *irq_to_pending(struct vcpu *v, 
unsigned int irq)
 
 struct pending_irq *spi_to_pending(struct domain *d, unsigned int irq)
 {
-    unsigned int idx;
-
     ASSERT(irq >= NR_LOCAL_IRQS);
 
     if ( is_espi(irq) )
-    {
-        unsigned int nr_spis = d->arch.vgic.nr_spis;
+        return espi_to_pending(d, irq);
 
-        idx = espi_intid_to_idx(irq) + nr_spis;
-    }
-    else
-    {
-        idx = irq - NR_LOCAL_IRQS;
-    }
-
-    return &d->arch.vgic.pending_irqs[idx];
+    return &d->arch.vgic.pending_irqs[irq - NR_LOCAL_IRQS];
 }
 
 void vgic_clear_pending_irqs(struct vcpu *v)
-- 
2.53.0