[xen stable-4.15] x86: avoid wrong use of all-but-self IPI shorthand

[patchbot@xxxxxxx]

commit 12c6ce12a1996df1e53ee1f35e1b6132771256f3
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Jan 7 08:14:13 2022 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Jan 7 08:14:13 2022 +0100

    x86: avoid wrong use of all-but-self IPI shorthand
    
    With "nosmp" I did observe a flood of "APIC error on CPU0: 04(04), Send
    accept error" log messages on an AMD system. And rightly so - nothing
    excludes the use of the shorthand in send_IPI_mask() in this case. Set
    "unaccounted_cpus" to "true" also when command line restrictions are the
    cause.
    
    Note that PV-shim mode is unaffected by this change, first and foremost
    because "nosmp" and "maxcpus=" are ignored in this case.
    
    Fixes: 5500d265a2a8 ("x86/smp: use APIC ALLBUT destination shorthand when 
possible")
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: 7621880de0bb40bae6436a5b106babc0e4718f4d
    master date: 2021-12-10 10:26:52 +0100
---
 xen/arch/x86/mpparse.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/mpparse.c b/xen/arch/x86/mpparse.c
index dff02b142b..91fa580831 100644
--- a/xen/arch/x86/mpparse.c
+++ b/xen/arch/x86/mpparse.c
@@ -85,9 +85,14 @@ void __init set_nr_cpu_ids(unsigned int max_cpus)
        if (!park_offline_cpus)
                tot_cpus = max_cpus;
        nr_cpu_ids = min(tot_cpus, NR_CPUS + 0u);
-       if (park_offline_cpus && nr_cpu_ids < num_processors)
-               printk(XENLOG_WARNING "SMP: Cannot bring up %u further CPUs\n",
-                      num_processors - nr_cpu_ids);
+       if (nr_cpu_ids < num_processors)
+       {
+               unaccounted_cpus = true;
+               if (park_offline_cpus)
+                       printk(XENLOG_WARNING
+                              "SMP: Cannot bring up %u further CPUs\n",
+                              num_processors - nr_cpu_ids);
+       }
 
 #ifndef nr_cpumask_bits
        nr_cpumask_bits = ROUNDUP(nr_cpu_ids, BITS_PER_LONG);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.15