[PATCH] x86/CPU: Add a tlbi= cmdline switch

[Borislav Petkov]

Ok,

here's what I have. I've tagged it for stable so that it goes everywhere and
we have the capability of disabling TLBI. I'm thinking of queueing it next
week.

Thx.

---

From: Rik van Riel <riel@xxxxxxxxxxx>
Date: Wed, 29 Jul 2026 20:43:41 -0400

With the recently found INVLPGB / TLBSYNC issue, there has been some
interest in disabling INVLPGB-based TLB flushing, in order to rule out
that CPU issue as a cause of userspace crashes.

Add a kernel command line option to control the TLB flushing behavior.

If the need arises, we will add a "tlbi=broadcast" for the case when TLB
invalidation broadcasts need to be explicitly selected, but this is not
needed now yet.

  [ bp: Rewrite commit message, move to cpu/common.c, add documentation. ]

Fixes: 767ae437a32d ("x86/mm: Add INVLPGB feature and Kconfig entry")
Suggested-by: Borislav Petkov <bp@xxxxxxxxx>
Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Link: https://patch.msgid.link/20260729204341.3eb0b5ea@fangorn
---
 Documentation/admin-guide/kernel-parameters.txt |  4 ++++
 arch/x86/kernel/cpu/common.c                    | 10 ++++++++++
 2 files changed, 14 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 87bb1fb31696..6f7a50d2af61 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -7568,6 +7568,10 @@ Kernel parameters
 			See Documentation/admin-guide/mm/transhuge.rst for more
 			details.
 
+	tlbi=		[X86-64]
+			Format: {ipi}
+			ipi: switch to IPI-based TLB flushing
+
 	topology=	[S390,EARLY]
 			Format: {off | on}
 			Specify if the kernel should make use of the cpu
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index e84ddf6bb10d..30134d189dae 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2675,3 +2675,13 @@ void __init arch_cpu_finalize_init(void)
 	 */
 	mem_encrypt_init();
 }
+
+/* Control TLB flushing methods */
+static int __init tlbi_setup(char *str)
+{
+	if (!strcmp(str, "ipi"))
+		setup_clear_cpu_cap(X86_FEATURE_INVLPGB);
+
+	return 1;
+}
+__setup("tlbi=", tlbi_setup);
-- 
2.53.0


-- 
Regards/Gruss,
    Boris.

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