Re: Consuming PCI device in PV kernel

[Andrew Cooper <andrew.cooper3@citrix.com>]

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