linux-kernel - Re: [PATCH v4 12/17] x86/asm/entry/64: Save all regs on interrupt entry

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Date:	Thu, 2 Jul 2015 08:33:28 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4 12/17] x86/asm/entry/64: Save all regs on interrupt entry

On Thu, Jul 2, 2015 at 3:52 AM, Borislav Petkov <bp@...en8.de> wrote:
> On Mon, Jun 29, 2015 at 12:33:44PM -0700, Andy Lutomirski wrote:
>> To prepare for the big rewrite of the error and interrupt exit
>> paths, we will need pt_regs completely filled in.  It's already
>> completely filled in when error_exit runs, so rearrange interrupt
>> handling to match it.  This will slow down interrupt handling very
>> slightly (eight instructions), but the simplification it enables
>> will be more than worth it.
>>
>> Signed-off-by: Andy Lutomirski <luto@...nel.org>
>> ---
>>  arch/x86/entry/entry_64.S | 29 +++++++++--------------------
>>  1 file changed, 9 insertions(+), 20 deletions(-)
>>
>> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
>> index 9bc76766aa71..51d34fafe4c0 100644
>> --- a/arch/x86/entry/entry_64.S
>> +++ b/arch/x86/entry/entry_64.S
>> @@ -502,21 +502,13 @@ END(irq_entries_start)
>>  /* 0(%rsp): ~(interrupt number) */
>>       .macro interrupt func
>>       cld
>> -     /*
>> -      * Since nothing in interrupt handling code touches r12...r15 members
>> -      * of "struct pt_regs", and since interrupts can nest, we can save
>> -      * four stack slots and simultaneously provide
>> -      * an unwind-friendly stack layout by saving "truncated" pt_regs
>> -      * exactly up to rbp slot, without these members.
>> -      */
>> -     ALLOC_PT_GPREGS_ON_STACK -RBP
>> -     SAVE_C_REGS -RBP
>> -     /* this goes to 0(%rsp) for unwinder, not for saving the value: */
>> -     SAVE_EXTRA_REGS_RBP -RBP
>
> That macro's unused now AFAICT.
>

I'll delete it in v5.

--Andy

> --
> Regards/Gruss,
>     Boris.
>
> ECO tip #101: Trim your mails when you reply.
> --



-- 
Andy Lutomirski
AMA Capital Management, LLC
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