Re: [Xen-devel] [PATCH 2/4] x86: correct instances of PGC_allocated clearing

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.11.18 at 17:59, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 20/11/2018 16:18, Jan Beulich wrote:
>> For domain heap pages assigned to a domain dropping the page reference
>> tied to PGC_allocated may not drop the last reference, as otherwise the
>> test_and_clear_bit() might already act on an unowned page.
>>
>> Work around this where possible, but the need to acquire extra page
>> references is a fair hint that references should have been acquired in
>> other places instead.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> Compile tested only, as I have neither a mem-sharing nor a mem-paging
>> environment set up ready to be used for such testing.
> 
> Perhaps we should compile them out by default?  It's clear there are no
> production users, given the quality of the code and how many security
> issues we spot accidentally.

Yeah, well - if we're going to have a perhaps much wider set of
config options, then these two surely should become "default n"
until they've been brought out of their sorry state.

> Either way, the code looks plausible.  Acked-by: Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>

Thanks.

Jan



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