linux-kernel - Re: [tip:x86/asm] x86/asm/msr: Make wrmsrl

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Message-ID: <20150605100442.GA8995@gmail.com>
Date:	Fri, 5 Jun 2015 12:04:42 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-tip-commits@...r.kernel.org,
	tip-bot for Andy Lutomirski <tipbot@...or.com>,
	peterz@...radead.org, torvalds@...ux-foundation.org,
	luto@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
	akpm@...ux-foundation.org
Subject: Re: [tip:x86/asm] x86/asm/msr: Make wrmsrl_safe() a function

* H. Peter Anvin <hpa@...or.com> wrote:

> Shouldn't we make it a proper function sine there is going to have to be a 
> function call involved anyway?

Yeah, so what I think should be done instead is to flip around the API:
make wrmsrl_safe() the primary API and derive wrmsr_safe() from that,
because it's the saner API and because we have 3 times more wrmsrl_safe()
users right now!

And I'd make _that_ mapping inline, which would catch crap like:

  ./arch/x86/include/asm/msr.h:   return wrmsr_safe(msr, (u32)val,  (u32)(val >> 32));
  ./arch/x86/xen/enlighten.c:     wrmsr_safe(msr, (u32)pfn, (u32)(pfn >> 32));

and would turn it back into wrmsrl_safe(pfn)/etc. seemlessly.

In addition to that we might even phase out the high/low API altogether, as code 
like this:

            !wrmsr_safe(MSR_EFER,
                        header->pmode_efer_low,
                        header->pmode_efer_high))

should probably use a single u64.

But crappy paravirt indirections get in the way of an easy, trivial restructuring, 
as usual...

Thanks,

	Ingo
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