linux-kernel - Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*

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Message-ID: <535F205F.9040101@zytor.com>
Date:	Mon, 28 Apr 2014 20:45:35 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Andrew Lutomirski <amluto@...il.com>
CC:	comex <comexk@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Borislav Petkov <bp@...en8.de>,
	Arjan van de Ven <arjan.van.de.ven@...el.com>,
	Brian Gerst <brgerst@...il.com>,
	Alexandre Julliard <julliard@...ehq.com>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*

On 04/28/2014 07:38 PM, H. Peter Anvin wrote:
> On 04/28/2014 05:20 PM, Andrew Lutomirski wrote:
>>
>> ldttest segfaults on 3.13 and 3.14 for me.  It reboots (triple fault?)
>> on your branch.  It even said this:
>>
>> qemu-system-x86_64: 9pfs:virtfs_reset: One or more uncluncked fids
>> found during reset
>>
>> I have no idea what an uncluncked fd is :)
>>
> 
> It means 9p wasn't properly shut down.
> 

OK, so I found a bug in ldttest.c -- it sets CS to an LDT segment, but
it never sets SS to an LDT segment.  This means that it should really
have zero footprint versus the espfix code, and implies that we instead
have another bug involved.  Why the espfix code should have any effect
whatsoever is a mystery, however... if it indeed does?

I have uploaded a fixed ldttest.c, but it seems we might be chasing more
than that...

	-hpa


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