git: 40c01de13562 - stable/13 - x86: Short-circuit ipi_all_but_self() on UP systems

The branch stable/13 has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=40c01de1356224a82fec217bd3cd59dd058ef095

commit 40c01de1356224a82fec217bd3cd59dd058ef095
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2025-01-07 17:58:58 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2025-01-14 14:14:45 +0000

    x86: Short-circuit ipi_all_but_self() on UP systems
    
    Apparently this is required on old intel hw, see
    https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275086#c3
    
    PR:             275086
    Reviewed by:    mav, kib
    Fixes:          279cd05b7e4d ("Use APIC_IPI_DEST_OTHERS for bitmapped IPIs too.")
    MFC after:      1 week
    Diagnosed by:   Ben Wilber <ben@desync.com>
    Differential Revision:  https://reviews.freebsd.org/D48361
    
    (cherry picked from commit 254a2b767f9a39f1541e0a07a70bbe269e86ad70)
---
 sys/x86/x86/mp_x86.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/sys/x86/x86/mp_x86.c b/sys/x86/x86/mp_x86.c
index 56cf7e426076..771cf95f36b4 100644
--- a/sys/x86/x86/mp_x86.c
+++ b/sys/x86/x86/mp_x86.c
@@ -1424,6 +1424,9 @@ ipi_all_but_self(u_int ipi)
 	cpuset_t other_cpus;
 	int cpu, c;
 
+	if (mp_ncpus == 1)
+		return;
+
 	/*
 	 * IPI_STOP_HARD maps to a NMI and the trap handler needs a bit
 	 * of help in order to understand what is the source.