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

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Message-ID: <53C45857.6050605@zytor.com>
Date:	Mon, 14 Jul 2014 15:23:19 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	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 07/14/2014 02:35 PM, Andy Lutomirski wrote:
> Presumably the problem is here:
> 
> ENTRY(xen_iret)
>     pushq $0
> 1:    jmp hypercall_iret
> ENDPATCH(xen_iret)
> 
> This seems rather unlikely to work on the espfix stack.
> 
> Maybe espfix64 should be disabled when running on Xen and Xen should
> implement its own espfix64 in the hypervisor.

Perhaps the first question is: is espfix even necessary on Xen?  How
does the Xen PV IRET handle returning to a 16-bit stack segment?

	-hpa


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