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

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Message-ID: <555B5105.4040808@zytor.com>
Date:	Tue, 19 May 2015 08:04:37 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...nel.org>
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

On 05/18/2015 12:43 PM, Andy Lutomirski wrote:
> On 05/15/2015 12:27 AM, H. Peter Anvin wrote:
>> On 05/14/2015 11:54 PM, Ingo Molnar wrote:
>>>
>>> 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.
>>>
>>
>> It doesn't hurt, although it isn't super critical as each page will be
>> shared among 64 CPUs.  The whole espfix stack is only a single cacheline
>> long.
>>
> 
> I don't think we actually need these pages allocated until we try to run
> user code.  Can we move this very late in initialization instead?
> 

Yes, we could, as long as it is run on each CPU before that CPU tries to
run user code.

	-hpa


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