Re: [Xen-devel] [PATCH RFC 2/4] xen: grant_table: implement grant_table_soft_reset()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.06.15 at 16:58, <vkuznets@xxxxxxxxxx> wrote:
> "Jan Beulich" <JBeulich@xxxxxxxx> writes:
> 
>>>>> On 03.06.15 at 15:35, <vkuznets@xxxxxxxxxx> wrote:
>>> When soft reset is being performed we need to replace all actively
>>> granted pages with empty pages to prevent possible future memory
>>> corruption as the newly started kernel won't be aware of these
>>> granted pages.
>>> 
>>> We make the tot_pages < max_pages assumption here: previously granted pages
>>> need to belong to someone and we don't want to implement possible DoS by
>>> reassigning them to the grantee/anonymous domain/xen/.. (the malicious guest
>>> will be able to consume all host's memory).
>>
>> How is that going to look in practice? I.e. won't this cause frequent
>> failures?
>>
> 
> I'm not sure we actually need that in practice. In my testing backends
> (even with persistent grants enabled) collaborate nicely and release all
> grants. I can see a single page still being held and I suppose it's
> being held by QEMU (haven't checked what that but I think it is the
> console ring). In case we go for the toolstack-assisted approach we can
> restart qemu and add some warning when there are active grants.

But even a single page could cause the allocation to fail because of
otherwise going over the set limit.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel