[PATCH] xen/arm: vtimer: Don't read/use the secure physical timer interrupt for ACPI

[Julien Grall <julien@xxxxxxx>]

From: Julien Grall <jgrall@xxxxxxxxxx>

Per ACPI 6.5 section 5.2.25 ("Generic Timer Description Table (GTDT)"),
the fields "Secure EL1 Timer GSIV/Flags" are optional and an OS running
in non-secure world is meant to ignore the values.

However, Xen is trying to reserve the value. When booting on Graviton
2 metal instances, this would result to crash a boot because the
value is 0 which is already reserved (I haven't checked for which device).
While nothing prevent a PPI to be shared, the field should have been
ignored by Xen.

For the Device-Tree case, I couldn't find a statement suggesting
that the secure physical timer interrupt  is ignored. In fact, I have
found some code in Linux using it as a fallback. That said, it should
never be used.

As I am not aware of any issue when booting using Device-Tree, the
physical timer interrupt is only ignored for ACPI.

Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>

----

This has not been tested on Graviton 2 because I can't seem to get
the serial console working properly. @Dan would you be able to try it?

It would also be good to understand why 0 why already reserved. This
may be a sign for other issues in the ACPI code.
---
 xen/arch/arm/time.c   |  4 ----
 xen/arch/arm/vtimer.c | 17 +++++++++++++++--
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/xen/arch/arm/time.c b/xen/arch/arm/time.c
index 3535bd8ac7c7..8fc14cd3ff62 100644
--- a/xen/arch/arm/time.c
+++ b/xen/arch/arm/time.c
@@ -78,10 +78,6 @@ static int __init arch_timer_acpi_init(struct 
acpi_table_header *header)
     irq_set_type(gtdt->non_secure_el1_interrupt, irq_type);
     timer_irq[TIMER_PHYS_NONSECURE_PPI] = gtdt->non_secure_el1_interrupt;
 
-    irq_type = acpi_get_timer_irq_type(gtdt->secure_el1_flags);
-    irq_set_type(gtdt->secure_el1_interrupt, irq_type);
-    timer_irq[TIMER_PHYS_SECURE_PPI] = gtdt->secure_el1_interrupt;
-
     irq_type = acpi_get_timer_irq_type(gtdt->virtual_timer_flags);
     irq_set_type(gtdt->virtual_timer_interrupt, irq_type);
     timer_irq[TIMER_VIRT_PPI] = gtdt->virtual_timer_interrupt;
diff --git a/xen/arch/arm/vtimer.c b/xen/arch/arm/vtimer.c
index c54360e20266..e73ae33c1b58 100644
--- a/xen/arch/arm/vtimer.c
+++ b/xen/arch/arm/vtimer.c
@@ -8,6 +8,7 @@
  * Copyright (c) 2011 Citrix Systems.
  */
 
+#include <xen/acpi.h>
 #include <xen/lib.h>
 #include <xen/perfc.h>
 #include <xen/sched.h>
@@ -61,10 +62,22 @@ int domain_vtimer_init(struct domain *d, struct 
xen_arch_domainconfig *config)
 
     config->clock_frequency = timer_dt_clock_frequency;
 
-    /* At this stage vgic_reserve_virq can't fail */
+    /*
+     * Per the ACPI specification, providing a secure EL1 timer
+     * interrupt is optional and will be ignored by non-secure OS.
+     * Therefore don't reserve the interrupt number for the HW domain
+     * and ACPI.
+     *
+     * Note that we should still reserve it when using the Device-Tree
+     * because the interrupt is not optional. That said, we are not
+     * expecting any OS to use it when running on top of Xen.
+     *
+     * At this stage vgic_reserve_virq() is not meant to fail.
+    */
     if ( is_hardware_domain(d) )
     {
-        if ( !vgic_reserve_virq(d, timer_get_irq(TIMER_PHYS_SECURE_PPI)) )
+        if ( acpi_disabled &&
+             !vgic_reserve_virq(d, timer_get_irq(TIMER_PHYS_SECURE_PPI)) )
             BUG();
 
         if ( !vgic_reserve_virq(d, timer_get_irq(TIMER_PHYS_NONSECURE_PPI)) )
-- 
2.40.1