Re: [PATCH] tools/xenstore: don't store domU's mfn of ring page in xensotred

[Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>]

On 29/04/2020 14:06, Jürgen Groß wrote:
> On 29.04.20 14:49, Igor Druzhinin wrote:
>> On 29/04/2020 13:29, Jürgen Groß wrote:
>>> On 29.04.20 13:04, Igor Druzhinin wrote:
>>
>> Yes, XAPI is doing soft reset differently from libxl. You need to keep 
>> xenstore
>> data to at least keep backends working without the need to reinitialize them
>> before entering kdump kernel. We do the same thing while entering crash 
>> kernel
>> in Windows after BSOD (CC Paul as he recommended this approach).
>> There are other reasons to not reset xenstore data.
>>
>> I considered XS_INTRODUCE functionality to be part of xenstored ABI and we 
>> built
>> a lot of infrastructure on top of that. So I don't think it could be easily 
>> removed now.
> 
> Nobody wants to remove XS_INTRODUCE. It was just questioned there is a
> need to call XS_INTRODUCE multiple times for a domain without a call of
> XS_RELEASE in between.

Sorry, I didn't mean the whole XS_INTRODUCE but that particular bit that
allows it to rebind the channels without calling XS_RELEASE first as the
latter has a lot of implications from toolstack point of view.

> In case there is such a need this means we either should just drop the
> test for the mfn to match and recreate the event-channel (which will do
> no harm IMO), or we need to keep the mfn in the live-update state record
> with the knowledge that it is far from being a good indicator for the
> test whether a domain is known already or not (two HVM domains using a
> similar configuration with the very same kernel will use the same gfn
> probably).
> 
> As only dom0 is allowed to use XS_INTRODUCE and I'm not aware of any
> problems with neither XS_INTRODUCE failing due to illegal calls (no mfn
> match), nor with potentially recreating the event channel for a "wrong"
> domain, I suggest to just allow XS_INTRODUCE to be called as often as
> the toolstack wants to.

If that means keeping the current semantics of XS_INTRODUCE - I'd be quite
happy with that.

Igor