linux-kernel - Re: [RFC/INCOMPLETE 08/13] x86/entry/64: Migrate 64-bit syscalls to new exit hooks

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Date:	Thu, 18 Jun 2015 12:17:09 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
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>,
	Borislav Petkov <bp@...en8.de>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC/INCOMPLETE 08/13] x86/entry/64: Migrate 64-bit syscalls to
 new exit hooks


* Andy Lutomirski <luto@...capital.net> wrote:

> >> Any reason why irq state tracking cannot be done in C as well, like the rest 
> >> of the irq state tracking code?
> >
> > Never mind, I see you've done exactly that in patch #12.
> 
> There are still some TRACE_IRQS_ON, LOCKDEP_SYS_EXIT, and such scattered 
> throughout the asm.  it's plausible that even more of that could be moved to C.
> 
> We could also benchmark and find out how bad it would be if we just always 
> filled pt_regs in completely in syscalls.  If the performance hit isn't enough 
> to matter, then we could potentially move the entire syscall path except pt_regs 
> setup and sysret/iret into three C functions.

The thing is, I'd not be against simplifying pt_regs handling even if it slows 
down things a tiny bit. If anyone wants to reintroduce that complexity we'll see 
how it looks like in isolation, done cleanly.

Thanks,

	Ingo
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