xen: allow up to 16383 cpus

With lock handling now allowing up to 16384 cpus (spinlocks can handle
65535 cpus, rwlocks can handle 16384 cpus), raise the allowed limit for
the number of cpus to be configured to 16383.

The new limit is imposed by IOMMU_CMD_BUFFER_MAX_ENTRIES and
QINVAL_MAX_ENTRY_NR required to be larger than 2 * CONFIG_NR_CPUS.

Add a support limit of physical CPUs to SUPPORT.md (4096 on x86, 128
on ARM).

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <jgrall@amazon.com>

CHANGELOG.md

@@ -14,6 +14,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
    - HVM PIRQs are disabled by default.
    - Reduce IOMMU setup time for hardware domain.
  - xl/libxl configures vkb=[] for HVM domains with priority over vkb_device.
+ - Increase the maximum number of CPUs Xen can be built for from 4095 to
+   16383.
 
 ### Added
  - On x86:

SUPPORT.md

@@ -61,6 +61,11 @@ For the Cortex A77 r0p0 - r1p0, see Errata 1508412.
 
     Status, x86: Supported
 
+### Physical CPUs
+
+    Status, x86: Supported up to 4096
+    Status, ARM: Supported up to 128
+
 ### Host ACPI (via Domain 0)
 
     Status, x86 PV: Supported

xen/arch/Kconfig

@@ -6,7 +6,7 @@ config PHYS_ADDR_T_32
 
 config NR_CPUS
 	int "Maximum number of CPUs"
-	range 1 4095
+	range 1 16383
 	default "256" if X86
 	default "8" if ARM && RCAR3
 	default "4" if ARM && QEMU