[PATCH 7.1 229/271] x86/CPU: Add a tlbi= cmdline switch

7.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Rik van Riel <[email protected]>

commit abe7c8b09bd72a9c726016257c6281f129b4c02d upstream.

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 <[email protected]>
Signed-off-by: Rik van Riel <[email protected]>
Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Cc: <[email protected]>
Link: https://patch.msgid.link/20260729204341.3eb0b5ea@fangorn
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 Documentation/admin-guide/kernel-parameters.txt |    4 ++++
 arch/x86/kernel/cpu/common.c                    |   10 ++++++++++
 2 files changed, 14 insertions(+)

--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -7573,6 +7573,10 @@ 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
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2668,3 +2668,13 @@ 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);