linux-kernel - [tip:x86/pti] x86/entry/64: Drop idtentry's manual stack switch for user entries

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Date:   Mon, 9 Apr 2018 10:11:25 -0700
From:   tip-bot for Andy Lutomirski <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     luto@...nel.org, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, mingo@...nel.org,
        peterz@...radead.org, linux@...inikbrodowski.net, hpa@...or.com,
        tglx@...utronix.de, bp@...en8.de
Subject: [tip:x86/pti] x86/entry/64: Drop idtentry's manual stack switch for
 user entries

Commit-ID:  071ccc966ba5db1ac8f5c24b0faebb37698f68db
Gitweb:     https://git.kernel.org/tip/071ccc966ba5db1ac8f5c24b0faebb37698f68db
Author:     Andy Lutomirski <luto@...nel.org>
AuthorDate: Tue, 3 Apr 2018 15:39:26 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 9 Apr 2018 18:23:50 +0200

x86/entry/64: Drop idtentry's manual stack switch for user entries

For non-paranoid entries, idtentry knows how to switch from the
kernel stack to the user stack, as does error_entry.  This results
in pointless duplication and code bloat.  Make idtentry stop
thinking about stacks for non-paranoid entries.

This reduces text size by 5377 bytes.

This goes back to the following commit:

  7f2590a110b8 ("x86/entry/64: Use a per-CPU trampoline stack for IDT entries")

Signed-off-by: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dominik Brodowski <linux@...inikbrodowski.net>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/90aab80c1f906e70742eaa4512e3c9b5e62d59d4.1522794757.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/entry/entry_64.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 9b114675fbc0..e237913a056b 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -908,7 +908,7 @@ ENTRY(\sym)
 	pushq	$-1				/* ORIG_RAX: no syscall to restart */
 	.endif
 
-	.if \paranoid < 2
+	.if \paranoid == 1
 	testb	$3, CS-ORIG_RAX(%rsp)		/* If coming from userspace, switch stacks */
 	jnz	.Lfrom_usermode_switch_stack_\@
 	.endif
@@ -955,7 +955,7 @@ ENTRY(\sym)
 	jmp	error_exit
 	.endif
 
-	.if \paranoid < 2
+	.if \paranoid == 1
 	/*
 	 * Entry from userspace.  Switch stacks and treat it
 	 * as a normal entry.  This means that paranoid handlers