git: 8b2546469323 - stable/14 - x86_msr_op(9): consistently return the value read from MSR

The branch stable/14 has been updated by olce:

URL: https://cgit.FreeBSD.org/src/commit/?id=8b2546469323c72a954d4c0c1202d0845b80c3ee

commit 8b2546469323c72a954d4c0c1202d0845b80c3ee
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2026-02-04 00:24:58 +0000
Commit:     Olivier Certner <olce@FreeBSD.org>
CommitDate: 2026-07-23 09:59:00 +0000

    x86_msr_op(9): consistently return the value read from MSR
    
    If the operation is executed on more than one CPU, a random instance of
    the read value is returned.
    
    Reviewed by:    markj, olce
    Sponsored by:   The FreeBSD Foundation
    MFC after:      1 week
    Differential revision:  https://reviews.freebsd.org/D55045
    
    (cherry picked from commit 36ceb5509d01ff2e6482a78ca809c344574e9a25)
---
 sys/x86/x86/cpu_machdep.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/sys/x86/x86/cpu_machdep.c b/sys/x86/x86/cpu_machdep.c
index 6e49a25f8ece..0228e127419b 100644
--- a/sys/x86/x86/cpu_machdep.c
+++ b/sys/x86/x86/cpu_machdep.c
@@ -137,6 +137,8 @@ x86_msr_op_one_safe(struct msr_op_arg *a)
 			atomic_cmpset_int(&a->error, 0, error);
 			break;
 		}
+		if (a->res != NULL)
+			atomic_store_64(a->res, v);
 		v &= ~a->arg1;
 		error = wrmsr_safe(a->msr, v);
 		if (error != 0)
@@ -148,6 +150,8 @@ x86_msr_op_one_safe(struct msr_op_arg *a)
 			atomic_cmpset_int(&a->error, 0, error);
 			break;
 		}
+		if (a->res != NULL)
+			atomic_store_64(a->res, v);
 		v |= a->arg1;
 		error = wrmsr_safe(a->msr, v);
 		if (error != 0)
@@ -160,10 +164,12 @@ x86_msr_op_one_safe(struct msr_op_arg *a)
 		break;
 	case MSR_OP_READ:
 		error = rdmsr_safe(a->msr, &v);
-		if (error == 0)
-			*a->res = v;
-		else
+		if (error == 0) {
+			if (a->res != NULL)
+				atomic_store_64(a->res, v);
+		} else {
 			atomic_cmpset_int(&a->error, 0, error);
+		}
 		break;
 	}
 }
@@ -176,11 +182,15 @@ x86_msr_op_one_unsafe(struct msr_op_arg *a)
 	switch (a->op) {
 	case MSR_OP_ANDNOT:
 		v = rdmsr(a->msr);
+		if (a->res != NULL)
+			atomic_store_64(a->res, v);
 		v &= ~a->arg1;
 		wrmsr(a->msr, v);
 		break;
 	case MSR_OP_OR:
 		v = rdmsr(a->msr);
+		if (a->res != NULL)
+			atomic_store_64(a->res, v);
 		v |= a->arg1;
 		wrmsr(a->msr, v);
 		break;
@@ -189,7 +199,8 @@ x86_msr_op_one_unsafe(struct msr_op_arg *a)
 		break;
 	case MSR_OP_READ:
 		v = rdmsr(a->msr);
-		*a->res = v;
+		if (a->res != NULL)
+			atomic_store_64(a->res, v);
 		break;
 	default:
 		__assert_unreachable();