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

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Message-Id: <90aab80c1f906e70742eaa4512e3c9b5e62d59d4.1522794757.git.luto@kernel.org>
Date:   Tue,  3 Apr 2018 15:39:26 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org, LKML <linux-kernel@...r.kernel.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH] 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 commit 7f2590a110b8 ("x86/entry/64: Use a per-CPU
trampoline stack for IDT entries").

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---

Hi all-

I have more cleanups in the works, but this is enough of I win by itself
that I wanted to get it out there.

 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
-- 
2.14.3