[PATCH] x86/cpufeatures: make clearcpuid=invlpgb work

[PATCH] x86/cpufeatures: make clearcpuid=invlpgb work

[Rik van Riel]

With the recently found INVLPGB / TLBSYNC issue, there has
been some interest in disabling invlpgb TLB flushing, in
order to rule out that issue wihle tracking down some
userspace crash.

The top search result shows "clearcpuid=invlpgb"

However, invlpgb is not actually in x86_cap_flags, so booting
with clearcpuid=invlpgb results in the following message:

  clearcpuid: unknown CPU flag: invlpgb

Adding "invlpgb" to the comment after X86_FEATURE_INVLPGB
causes mkcapflags.sh to pick up invlpgb, and add it to
x86_cap_flags.

With that change, clearcpuid=invlpgb works:

  clearcpuid: force-disabling CPU feature flag: invlpgb

Signed-off-by: Rik van Riel <riel@surriel.com>
---
 arch/x86/include/asm/cpufeatures.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 1b4a48bff18f..62fa2b0236af 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -332,7 +332,7 @@
 #define X86_FEATURE_CLZERO		(13*32+ 0) /* "clzero" CLZERO instruction */
 #define X86_FEATURE_IRPERF		(13*32+ 1) /* "irperf" Instructions Retired Count */
 #define X86_FEATURE_XSAVEERPTR		(13*32+ 2) /* "xsaveerptr" Always save/restore FP error pointers */
-#define X86_FEATURE_INVLPGB		(13*32+ 3) /* INVLPGB and TLBSYNC instructions supported */
+#define X86_FEATURE_INVLPGB		(13*32+ 3) /* "invplgb" INVLPGB and TLBSYNC instructions supported */
 #define X86_FEATURE_RDPRU		(13*32+ 4) /* "rdpru" Read processor register at user level */
 #define X86_FEATURE_WBNOINVD		(13*32+ 9) /* "wbnoinvd" WBNOINVD instruction */
 #define X86_FEATURE_AMD_IBPB		(13*32+12) /* Indirect Branch Prediction Barrier */
-- 
2.54.0

Re: [PATCH] x86/cpufeatures: make clearcpuid=invlpgb work

[Borislav Petkov]

On Wed, Jul 29, 2026 at 01:06:46PM -0400, Rik van Riel wrote:
> With the recently found INVLPGB / TLBSYNC issue, there has
> been some interest in disabling invlpgb TLB flushing, in
> order to rule out that issue wihle tracking down some
> userspace crash.

Yeah, except we discourage people from using clearcpuid= because that's
a hack.

Let's define a separate cmdline option now, pls, considering this is a valid
use case. And because writing it is looong and error prone and the feature
name is actually TLBI, we could do simply

tlbi=off

and everyone's happy.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette