git: e5f8cbb86d58 - main - x86: x86_msr_op(): MSR_OP_LOCAL: Disable interrupts on atomic ops

The branch main has been updated by olce:

URL: https://cgit.FreeBSD.org/src/commit/?id=e5f8cbb86d58f25b5ff168506b78d09dca266fb6

commit e5f8cbb86d58f25b5ff168506b78d09dca266fb6
Author:     Olivier Certner <olce@FreeBSD.org>
AuthorDate: 2026-01-23 20:52:46 +0000
Commit:     Olivier Certner <olce@FreeBSD.org>
CommitDate: 2026-02-03 14:03:01 +0000

    x86: x86_msr_op(): MSR_OP_LOCAL: Disable interrupts on atomic ops
    
    On MSR_OP_LOCAL and non-naturally-atomic operations (MSR_OP_ANDNOT and
    MSR_OP_OR), there is no guarantee that we are not interrupted between
    reading and writing the MSR, and that interruption could actually
    perform some operation on that MSR, which would be lost.
    
    Prevent that problem by temporarily disabling interrupts around MSR
    manipulation.
    
    Reviewed by:    kib
    Discussed with: markj
    MFC after:      2 weeks
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D54996
---
 sys/x86/include/x86_var.h | 2 ++
 sys/x86/x86/cpu_machdep.c | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/sys/x86/include/x86_var.h b/sys/x86/include/x86_var.h
index 701b982e6afb..215fe0562465 100644
--- a/sys/x86/include/x86_var.h
+++ b/sys/x86/include/x86_var.h
@@ -171,6 +171,8 @@ uint64_t rdtsc_ordered(void);
 
 /*
  * Where and which execution mode
+ *
+ * All modes cause execution on the target CPU(s) with interrupts disabled.
  */
 #define	MSR_OP_LOCAL		0x10000000
 #define	MSR_OP_SCHED_ALL	0x20000000
diff --git a/sys/x86/x86/cpu_machdep.c b/sys/x86/x86/cpu_machdep.c
index 5cbcb40540bb..5f8965bd5614 100644
--- a/sys/x86/x86/cpu_machdep.c
+++ b/sys/x86/x86/cpu_machdep.c
@@ -160,6 +160,7 @@ x86_msr_op(u_int msr, u_int op, uint64_t arg1, uint64_t *res)
 	struct thread *td;
 	struct msr_op_arg a;
 	cpuset_t set;
+	register_t flags;
 	u_int exmode;
 	int bound_cpu, cpu, i, is_bound;
 
@@ -171,7 +172,9 @@ x86_msr_op(u_int msr, u_int op, uint64_t arg1, uint64_t *res)
 
 	switch (exmode) {
 	case MSR_OP_LOCAL:
+		flags = intr_disable();
 		x86_msr_op_one(&a);
+		intr_restore(flags);
 		break;
 	case MSR_OP_SCHED_ALL:
 		td = curthread;