Re: [Xen-devel] [PATCH] x86/efi: Reserve EFI properties table

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.05.17 at 18:21, <ross.lagerwall@xxxxxxxxxx> wrote:
> On 05/15/2017 02:52 PM, Julien Grall wrote:
>> Hi Andrew,
>>
>> On 08/05/17 17:29, Andrew Cooper wrote:
>>> On 08/05/17 17:17, Ross Lagerwall wrote:
>>>> Some EFI firmware implementations may place the EFI properties table in
>>>> RAM marked as BootServicesData, which Xen does not consider as reserved.
>>>> When dom0 tries to access the EFI properties table (which Linux >= 4.4
>>>> does), it crashes with a page fault.
>>>
>>> The pagefault is just a side effect of Linux blindly assuming that the
>>> ioremap() request succeeded.
>>>
>>> From Xen's point of view, Dom0 tries to map a page which doesn't belong
>>> to dom_xen, resulting a permission failure.
>>>
>>>>   Fix this by unconditionally
>>>> marking the EFI properties table as reserved in the E820, much like is
>>>> done with the dmi regions.
>>>>
>>>> Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
>>>
>>> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>
>>> This is probably also 4.9 material.
>>
>> It looks like Jan had some comments on this patch. I haven't seen any
>> reply from Ross, I will wait before looking from a release perspective.
> 
> Jan had some comments on that patch but essentially NAKed it on
> principle so I don't think it will be going into 4.9.

Let me clarify the NAK a little: Besides there having been no
opposition to it (indicating to me that the grounds on which I gave
it are acceptable), I'd revisit this if a serious attempt was made to
make Linux behave sanely here, and that attempt was (bogusly)
rejected. After all Linux is already prepared to deal with there not
being any EFI memory map, so it would seem pretty strange to me
if they didn't accept a (presumably small) change to skip retrieving
the properties table in that case (and perhaps at once the
memory attributes one). (And btw, I seem to recall indication that
the Dom0 boot problem was due to an unchecked ioremap() or
alike call, but afaict 4.11 does have a check there, so I'm currently
at a loss to see where the boot failure would come from.)

Jan


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