[PATCH v4 18/30] x86/kvm/vmx: Mark vmx_l1d_should flush and vmx_l1d_flush_cond keys as allowed in .noinstr

Valentin Schneider
2025-01-14T18:00:41Z

Later commits will cause objtool to warn about static keys being used in
.noinstr sections in order to safely defer instruction patching IPIs
targeted at NOHZ_FULL CPUs.

These keys are used in .noinstr code, and can be modified at runtime
(/proc/kernel/vmx* write). However it is not expected that they will be
flipped during latency-sensitive operations, and thus shouldn't be a source
of interference wrt the text patching IPI.

Mark it to let objtool know not to warn about it.

Reported-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
---
arch/x86/kvm/vmx/vmx.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 893366e537322..a028c38f44e02 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -225,8 +225,15 @@ module_param(pt_mode, int, S_IRUGO);

struct x86_pmu_lbr __ro_after_init vmx_lbr_caps;

-static DEFINE_STATIC_KEY_FALSE(vmx_l1d_should_flush);
-static DEFINE_STATIC_KEY_FALSE(vmx_l1d_flush_cond);
+/*
+ * Both of these static keys end up being used in .noinstr sections, however
+ * they are only modified:
+ * - at init
+ * - from a /proc/kernel/vmx* write
+ * thus during latency-sensitive operations they should remain stable.
+ */
+static DEFINE_STATIC_KEY_FALSE_NOINSTR(vmx_l1d_should_flush);
+static DEFINE_STATIC_KEY_FALSE_NOINSTR(vmx_l1d_flush_cond);
static DEFINE_MUTEX(vmx_l1d_flush_mutex);

/* Storage for pre module init parameter parsing */
--
2.43.0