linux-kernel - Re: [PATCH 02/11] x86: code shrink in paranoid

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Date:	Wed, 11 Feb 2015 22:13:57 +0100
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/11] x86: code shrink in paranoid_exit

On 02/11/2015 09:36 PM, Andy Lutomirski wrote:
> On Wed, Jan 14, 2015 at 1:48 PM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
>> RESTORE_EXTRA_REGS + RESTORE_C_REGS looks small, but it's
>> a lot of instructions (fourteen). Let's reuse them.
>>
>> Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
>> CC: Linus Torvalds <torvalds@...ux-foundation.org>
>> CC: Oleg Nesterov <oleg@...hat.com>
>> CC: Borislav Petkov <bp@...en8.de>
>> CC: "H. Peter Anvin" <hpa@...or.com>
>> CC: Andy Lutomirski <luto@...capital.net>
>> CC: Frederic Weisbecker <fweisbec@...il.com>
>> CC: X86 ML <x86@...nel.org>
>> CC: Alexei Starovoitov <ast@...mgrid.com>
>> CC: Will Drewry <wad@...omium.org>
>> CC: Kees Cook <keescook@...omium.org>
>> CC: linux-kernel@...r.kernel.org
>> ---
>>  arch/x86/kernel/entry_64.S | 6 ++----
>>  1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
>> index a21b5b3..f5e815e 100644
>> --- a/arch/x86/kernel/entry_64.S
>> +++ b/arch/x86/kernel/entry_64.S
>> @@ -1270,12 +1270,10 @@ ENTRY(paranoid_exit)
>>         jnz paranoid_restore
>>         TRACE_IRQS_IRETQ 0
>>         SWAPGS_UNSAFE_STACK
>> -       RESTORE_EXTRA_REGS
>> -       RESTORE_C_REGS
>> -       REMOVE_PT_GPREGS_FROM_STACK 8
>> -       INTERRUPT_RETURN
>> +       jmp paranoid_restore1
>>  paranoid_restore:
>>         TRACE_IRQS_IRETQ_DEBUG 0
>> +paranoid_restore1:
>>         RESTORE_EXTRA_REGS
>>         RESTORE_C_REGS
>>         REMOVE_PT_GPREGS_FROM_STACK 8
> 
> This is sort of a reply to the wrong thread, but wouldn't it be nicer
> if we could pop a bunch of regs instead of using mov followed by add?

I like this (pop instead of mov) too.

> (Yes, this could be a followup, but it could be easier to spot now by
> changing macros like RESTORE_XYZ.)

I don't understand what this means.
"Let's switch to pops now, in this patch"? Or something else?
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