[RFC 03/38] x86/hyperlaunch: convert max vcpu determination to domain builder

[Daniel P. Smith]

The domain configuration may request more vcpus than are present in the system.
For dom0, the function dom0_max_vcpus() was used to clamp down to physically
available vcpus. Here we are introducing a generalized version,
dom_max_vcpus(), that takes a boot domain and sets the max vcpus based on the
lesser of the requested max and the available vcpus.

Signed-off-by: Daniel P. Smith <dpsm...@apertussolutions.com>
---
 xen/arch/x86/domain-builder/Makefile      |  1 +
 xen/arch/x86/domain-builder/domain.c      | 38 +++++++++++++++++++++++
 xen/arch/x86/include/asm/domain-builder.h |  1 +
 xen/arch/x86/setup.c                      |  4 +--
 4 files changed, 42 insertions(+), 2 deletions(-)
 create mode 100644 xen/arch/x86/domain-builder/domain.c

diff --git a/xen/arch/x86/domain-builder/Makefile 
b/xen/arch/x86/domain-builder/Makefile
index b10cd56b286b..67024b5cb213 100644
--- a/xen/arch/x86/domain-builder/Makefile
+++ b/xen/arch/x86/domain-builder/Makefile
@@ -1,2 +1,3 @@
 obj-$(CONFIG_DOMAIN_BUILDER) += fdt.init.o
 obj-y += core.init.o
+obj-y += domain.init.o
diff --git a/xen/arch/x86/domain-builder/domain.c 
b/xen/arch/x86/domain-builder/domain.c
new file mode 100644
index 000000000000..f2277b9e3cf3
--- /dev/null
+++ b/xen/arch/x86/domain-builder/domain.c
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2024, Apertus Solutions, LLC
+ */
+
+#include <xen/cpumask.h>
+#include <xen/domain.h>
+#include <xen/init.h>
+#include <xen/sched.h>
+
+#include <asm/bootinfo.h>
+
+unsigned int __init dom_max_vcpus(struct boot_domain *bd)
+{
+    unsigned int limit = bd->mode & BUILD_MODE_PARAVIRT ?
+                                    MAX_VIRT_CPUS : HVM_MAX_VCPUS;
+
+    if ( bd->capabilities & BUILD_CAPS_CONTROL )
+        limit = dom0_max_vcpus();
+    else
+        limit = min(limit,
+                    (uint32_t)cpumask_weight(cpupool_valid_cpus(cpupool0)));
+
+    if ( bd->max_vcpus == 0 || bd->max_vcpus > limit )
+        bd->max_vcpus = limit;
+
+    return bd->max_vcpus;
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/arch/x86/include/asm/domain-builder.h 
b/xen/arch/x86/include/asm/domain-builder.h
index 7518b6ddf3b9..f37f73e2255b 100644
--- a/xen/arch/x86/include/asm/domain-builder.h
+++ b/xen/arch/x86/include/asm/domain-builder.h
@@ -8,5 +8,6 @@ int __init builder_get_cmdline(
     struct boot_info *bi, int offset, char *cmdline, size_t size);
 
 void builder_init(struct boot_info *bi);
+unsigned int dom_max_vcpus(struct boot_domain *bd);
 
 #endif
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 6a939ccede3f..86bbd7c72ccd 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1010,18 +1010,18 @@ static struct domain *__init create_dom0(struct 
boot_info *bi)
     char *cmdline = NULL;
     size_t cmdline_size;
     unsigned int create_flags = 0;
+    struct boot_domain *bd = &bi->domains[0];
     struct xen_domctl_createdomain dom0_cfg = {
         .flags = IS_ENABLED(CONFIG_TBOOT) ? XEN_DOMCTL_CDF_s3_integrity : 0,
         .max_evtchn_port = -1,
         .max_grant_frames = -1,
         .max_maptrack_frames = -1,
         .grant_opts = XEN_DOMCTL_GRANT_version(opt_gnttab_max_version),
-        .max_vcpus = dom0_max_vcpus(),
+        .max_vcpus = dom_max_vcpus(bd),
         .arch = {
             .misc_flags = opt_dom0_msr_relaxed ? XEN_X86_MSR_RELAXED : 0,
         },
     };
-    struct boot_domain *bd = &bi->domains[0];
     struct domain *d;
 
     if ( opt_dom0_pvh ||
-- 
2.30.2