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Date: Thu, 18 Jun 2015 12:17:09 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        Borislav Petkov <bp@alien8.de>, Kees Cook <keescook@chromium.org>,
        Brian Gerst <brgerst@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [RFC/INCOMPLETE 08/13] x86/entry/64: Migrate 64-bit syscalls to
 new exit hooks
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* Andy Lutomirski <luto@amacapital.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