linux-kernel - [PATCH v5 19/25] KVM: VMX: Mark vmx_l1d_should flush and vmx_l1d_flush

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Message-ID: <20250429113242.998312-20-vschneid@redhat.com>
Date: Tue, 29 Apr 2025 13:32:36 +0200
From: Valentin Schneider <vschneid@...hat.com>
To: linux-kernel@...r.kernel.org,
	virtualization@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	loongarch@...ts.linux.dev,
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Cc: Josh Poimboeuf <jpoimboe@...nel.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Yair Podemsky <ypodemsk@...hat.com>,
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Subject: [PATCH v5 19/25] KVM: VMX: Mark vmx_l1d_should flush and vmx_l1d_flush_cond keys as allowed in .noinstr

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@...nel.org>
Signed-off-by: Valentin Schneider <vschneid@...hat.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 5c5766467a61d..00053458cd10c 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 */
-- 
2.49.0