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Date: Wed, 11 Feb 2015 22:13:57 +0100
From: Denys Vlasenko <dvlasenk@redhat.com>
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To: Andy Lutomirski <luto@amacapital.net>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Frederic Weisbecker <fweisbec@gmail.com>, X86 ML <x86@kernel.org>,
        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
        Kees Cook <keescook@chromium.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 02/11] x86: code shrink in paranoid_exit
References: <1421272101-16847-1-git-send-email-dvlasenk@redhat.com> <1421272101-16847-2-git-send-email-dvlasenk@redhat.com> <CALCETrWge6gKxZeVeFkVXtcHt8xByNXyGxhSjB7e9c1MWQLHKQ@mail.gmail.com>
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On 02/11/2015 09:36 PM, Andy Lutomirski wrote:
> On Wed, Jan 14, 2015 at 1:48 PM, Denys Vlasenko <dvlasenk@redhat.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@redhat.com>
>> CC: Linus Torvalds <torvalds@linux-foundation.org>
>> CC: Oleg Nesterov <oleg@redhat.com>
>> CC: Borislav Petkov <bp@alien8.de>
>> CC: "H. Peter Anvin" <hpa@zytor.com>
>> CC: Andy Lutomirski <luto@amacapital.net>
>> CC: Frederic Weisbecker <fweisbec@gmail.com>
>> CC: X86 ML <x86@kernel.org>
>> CC: Alexei Starovoitov <ast@plumgrid.com>
>> CC: Will Drewry <wad@chromium.org>
>> CC: Kees Cook <keescook@chromium.org>
>> CC: linux-kernel@vger.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?