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Date: Wed, 29 Nov 2017 14:38:41 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
        Denys Vlasenko <dvlasenk@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, daniel.gruss@iaik.tugraz.at,
        hughd@google.com, keescook@google.com, linux-mm@kvack.org,
        michael.schwarz@iaik.tugraz.at, moritz.lipp@iaik.tugraz.at,
        richard.fellner@student.tugraz.at,
        Andy Lutomirski <luto@amacapital.net>
Subject: Re: [PATCH 4/6] x86/mm/kaiser: Support PCID without INVPCID
Message-ID: <20171129133841.mkphnjpryrffns43@hirez.programming.kicks-ass.net>
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On Wed, Nov 29, 2017 at 01:31:58PM +0100, Peter Zijlstra wrote:
> On Wed, Nov 29, 2017 at 11:33:05AM +0100, Peter Zijlstra wrote:
> > @@ -220,7 +215,27 @@ For 32-bit we have the following convent
> >  .macro SWITCH_TO_USER_CR3 scratch_reg:req
> >  	STATIC_JUMP_IF_FALSE .Lend_\@, kaiser_enabled_key, def=1
> >  	mov	%cr3, \scratch_reg
> > -	ADJUST_USER_CR3 \scratch_reg
> > +
> > +	/*
> > +	 * Test if the ASID needs a flush.
> > +	 */
> > +	push	\scratch_reg			/* preserve CR3 */
> 
> So I was just staring at disasm of a few functions and I noticed this
> one reads like push, while others read like pushq.
> 
> So does the stupid assembler thing really do a 32bit push if you provide
> it with a 64bit register?

N/m, I just really cannot read straight today. The pushq's were a mem64,
not a r64 argument to push.