linux-kernel - [PATCH v4 12/16] x86/vsyscall: Document the fact that vsyscall=emulate disables LASS

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Message-ID: <20240710160655.3402786-13-alexander.shishkin@linux.intel.com>
Date: Wed, 10 Jul 2024 19:06:48 +0300
From: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To: Andy Lutomirski <luto@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
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	Dave Hansen <dave.hansen@...el.com>
Subject: [PATCH v4 12/16] x86/vsyscall: Document the fact that vsyscall=emulate disables LASS

Since EMULATE mode of vsyscall disables LASS, because fixing the LASS
violations during the EMULATE mode would need complex instruction
decoding, document this fact in kernel-parameters.txt.

Cc: Andy Lutomirski <luto@...nel.org>
Suggested-by: Dave Hansen <dave.hansen@...el.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 27ec49af1bf2..f7f06049353c 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -7247,7 +7247,9 @@
 
 			emulate     Vsyscalls turn into traps and are emulated
 			            reasonably safely.  The vsyscall page is
-				    readable.
+				    readable.  This also disables the LASS
+				    feature to allow userspace to poke around
+				    the vsyscall page.
 
 			xonly       [default] Vsyscalls turn into traps and are
 			            emulated reasonably safely.  The vsyscall
-- 
2.43.0