linux-kernel - Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init

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Date:	Mon, 18 Jan 2016 11:45:18 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...e.de>, Andy Lutomirski <luto@...capital.net>
Cc:	Brian Gerst <brgerst@...il.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after
 init

On 01/18/16 10:39, Borislav Petkov wrote:
> On Mon, Jan 18, 2016 at 10:29:24AM -0800, Andy Lutomirski wrote:
>> I think that, if we can make static_cpu_has be unconditionally safe as
>> a result
> 
> Problem with this is the additional .altinstructions entry for
> X86_FEATURE_ALWAYS. And sometimes you don't really need to use the _safe
> variant when you know you're safe.
> 

I think the two-byte optimization is the real issue if there is one at
all.  I don't care about the inittext, and unless I'm misremembering
completely altinstructions also get ejected.

So I don't personally object to killing off the unsafe variant.

	-hpa