linux-kernel - Re: [RFC PATCH] x86, espfix: use spin

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Message-ID: <20150515065417.GB29973@gmail.com>
Date:	Fri, 15 May 2015 08:54:17 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Borislav Petkov <bp@...en8.de>, Gu Zheng <guz.fnst@...fujitsu.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [RFC PATCH] x86, espfix: use spin_lock rather than mutex


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

> On 05/14/2015 02:27 PM, Borislav Petkov wrote:
> > Remove stable@ from CC.
> > 
> > On Thu, May 14, 2015 at 08:29:55PM +0200, Ingo Molnar wrote:
> >> We could allocate them on the boot CPU side and hand them over to 
> >> the secondary CPU.
> > 
> > Yeah, something along those lines. I mean, they're allocated and 
> > in-use during the complete system lifetime, we might just as well 
> > allocate them all in one go. Btw, what's our allocator that early, 
> > memblock?
> > 
> > Still, what I find strange is why are we seeing this only now? Is 
> > it because it had to be a big box (cpu >= 128) or something else 
> > changed...?
> > 
> 
> Quite probable.  You don't really want to allocate them until you 
> know if a CPU at least exists, though.
> 
> I like Ingo's suggestion of allocating them before CPU bringup on 
> the initiating CPU.

The only slightly subtle detail with that is to use alloc_pages_node() 
with the secondary CPU's node, to make sure the espfix stack is 
NUMA-local to the CPU that is going to use it.

Thanks,

	Ingo
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