From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: Consuming PCI device in PV kernel
Date: Fri, 25 Jul 2014 14:50:18 +0100
Message-ID: <53D2609A.4000802@citrix.com>
References: <524794479.20140703121338@gmail.com>	<20140703180957.GD13710@konrad-lan.dumpdata.com>	<1376452421.20140707092147@gmail.com>	<1083121389.20140707122233@gmail.com>	<623751089.20140718153713@gmail.com>	<20140718190942.GG15947@laptop.dumpdata.com>	<538610044.20140721111330@gmail.com>	<1405940004.25022.10.camel@kazak.uk.xensource.com>	<357303711.20140725135638@gmail.com>	<1406293821.24842.8.camel@kazak.uk.xensource.com>	<1035381797.20140725142116@gmail.com>
	<1406295478.24842.15.camel@kazak.uk.xensource.com>
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To: Ian Campbell <Ian.Campbell@citrix.com>, Simon Martin <furryfuttock@gmail.com>
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On 25/07/14 14:37, Ian Campbell wrote:
> On Fri, 2014-07-25 at 14:21 +0100, Simon Martin wrote:
>> Hello Ian,
>>
>> Thanks for the response.
>>
>>>> I     have     tried     calling    HYPERCALL_update_va_mapping    and
>>>> HYPERCALL_mmu_update  and  they both fail. HYPERCALL_update_va_mapping
>>>> gives me the following in xl dmesg:
>>>>
>>>> (XEN) mm.c:1700:d292v0 Bad L1 flags 400000
>>>>
>>>> Looking at the code I can't see where bit 22 is being set!
>>> Without seeing you code I've no idea about this (even if I could see it,
>>> I dunno...)
>> Bit 22 is being set in Xen code.
> Hopefully someone who knows the x86 PV stuff can chime in then, I looked
> but can't see what this represents.

I suspect this would be:

/* Bit 22 of a 24-bit flag mask. This corresponds to bit 62 of a pte.*/
#define _PAGE_GNTTAB (1U<<22)

from include/asm-x86/x86_64/page.h

So you are attempting to update a pte which already has a granted page
in it.

~Andrew