linux-kernel - Re: [PATCH 01/23] x86, kaiser: prepare assembly for entry/exit CR3 switching

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Message-ID: <20171101204242.whvunv2yvgj2uw22@pd.tnic>
Date:   Wed, 1 Nov 2017 21:42:42 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        moritz.lipp@...k.tugraz.at, daniel.gruss@...k.tugraz.at,
        michael.schwarz@...k.tugraz.at, luto@...nel.org,
        torvalds@...ux-foundation.org, keescook@...gle.com,
        hughd@...gle.com, x86@...nel.org
Subject: Re: [PATCH 01/23] x86, kaiser: prepare assembly for entry/exit CR3
 switching

On Wed, Nov 01, 2017 at 11:27:48AM -0700, Dave Hansen wrote:
> This allows for a tiny optimization of Andy's that I realize I must have
> blown away at some point.  It lets us do a 32-bit-register instruction
> (and using %eXX) when checking KAISER_SWITCH_MASK instead of a 64-bit
> register via %rXX.
> 
> I don't feel strongly about maintaining that optimization it looks weird
> and surely doesn't actually do much.

Yeah, and consistent syntax would probably bring more.

> Thanks for catching that.  We can kill one of these.  I'm inclined to
> kill the first one.  Looking at the second one since we've just saved
> off ptregs, that should make %rdi safe to clobber without the push/pop
> at all.
> 
> Does that seem like it would work?

Yap, sounds about right.

Thx.

-- 
Regards/Gruss,
    Boris.

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