linux-kernel - Re: Is espfix64's double-fault thing OK on Xen?

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Message-ID: <53C40D83.3090501@zytor.com>
Date:	Mon, 14 Jul 2014 10:04:03 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Is espfix64's double-fault thing OK on Xen?

On 07/09/2014 04:17 PM, Andy Lutomirski wrote:
> This part in __do_double_fault looks fishy:
> 
>     cmpl $__KERNEL_CS,CS(%rdi)
>     jne do_double_fault
> 
> Shouldn't that be:
> 
>     test $3,CS(%rdi)
>     jnz do_double_fault
> 

No, it should be fine.  The *only* case where we need to do the espfix
magic is when we are on __KERNEL_CS.

	-hpa


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