[xen stable-4.16] core-parking: fix build with gcc12 and NR_CPUS=1

[patchbot@xxxxxxx]

commit 4a6bedefe589dab12182d6b974de8ea3b2fcc681
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Mar 21 13:50:18 2023 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Mar 21 13:50:18 2023 +0100

    core-parking: fix build with gcc12 and NR_CPUS=1
    
    Gcc12 takes issue with core_parking_remove()'s
    
        for ( ; i < cur_idle_nums; ++i )
            core_parking_cpunum[i] = core_parking_cpunum[i + 1];
    
    complaining that the right hand side array access is past the bounds of
    1. Clearly the compiler can't know that cur_idle_nums can only ever be
    zero in this case (as the sole CPU cannot be parked).
    
    Arrange for core_parking.c's contents to not be needed altogether, and
    then disable its building when NR_CPUS == 1.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: 4b0422f70feb4b1cd04598ffde805fc224f3812e
    master date: 2023-03-13 15:15:42 +0100
---
 xen/arch/x86/Kconfig              |  2 +-
 xen/arch/x86/platform_hypercall.c | 11 ++++++++---
 xen/arch/x86/sysctl.c             |  3 +++
 xen/common/Kconfig                |  1 +
 4 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
index 3c14096c80..8e2b504923 100644
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -8,7 +8,7 @@ config X86
        select ACPI_LEGACY_TABLES_LOOKUP
        select ALTERNATIVE_CALL
        select ARCH_SUPPORTS_INT128
-       select CORE_PARKING
+       imply CORE_PARKING
        select HAS_ALTERNATIVE
        select HAS_COMPAT
        select HAS_CPUFREQ
diff --git a/xen/arch/x86/platform_hypercall.c 
b/xen/arch/x86/platform_hypercall.c
index bf4090c942..c35e5669a4 100644
--- a/xen/arch/x86/platform_hypercall.c
+++ b/xen/arch/x86/platform_hypercall.c
@@ -725,12 +725,17 @@ ret_t 
do_platform_op(XEN_GUEST_HANDLE_PARAM(xen_platform_op_t) u_xenpf_op)
         case XEN_CORE_PARKING_SET:
             idle_nums = min_t(uint32_t,
                     op->u.core_parking.idle_nums, num_present_cpus() - 1);
-            ret = continue_hypercall_on_cpu(
-                    0, core_parking_helper, (void *)(unsigned long)idle_nums);
+            if ( CONFIG_NR_CPUS > 1 )
+                ret = continue_hypercall_on_cpu(
+                        0, core_parking_helper,
+                        (void *)(unsigned long)idle_nums);
+            else if ( idle_nums )
+                ret = -EINVAL;
             break;
 
         case XEN_CORE_PARKING_GET:
-            op->u.core_parking.idle_nums = get_cur_idle_nums();
+            op->u.core_parking.idle_nums = CONFIG_NR_CPUS > 1
+                                           ? get_cur_idle_nums() : 0;
             ret = __copy_field_to_guest(u_xenpf_op, op, u.core_parking) ?
                   -EFAULT : 0;
             break;
diff --git a/xen/arch/x86/sysctl.c b/xen/arch/x86/sysctl.c
index aff52a13f3..ff843eaee2 100644
--- a/xen/arch/x86/sysctl.c
+++ b/xen/arch/x86/sysctl.c
@@ -179,6 +179,9 @@ long arch_do_sysctl(
                 ret = -EBUSY;
                 break;
             }
+            if ( CONFIG_NR_CPUS <= 1 )
+                /* Mimic behavior of smt_up_down_helper(). */
+                return 0;
             plug = op == XEN_SYSCTL_CPU_HOTPLUG_SMT_ENABLE;
             fn = smt_up_down_helper;
             hcpu = _p(plug);
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 6443943889..c9f4b7f492 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -10,6 +10,7 @@ config COMPAT
 
 config CORE_PARKING
        bool
+       depends on NR_CPUS > 1
 
 config GRANT_TABLE
        bool "Grant table support" if EXPERT
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.16