Re: [PATCH v3 12/16] KVM: arm64: handle pending bit for LPIs in ITS emulation

[Marc Zyngier <marc.zyngier@arm.com>]

On 07/10/15 16:46, Pavel Fedin wrote:
>  Hello!
> 
>> Sure. And you then have to parse and validate all the tables each and
>> every time you're going to inject an interrupt (because the guest can
>> change the table content behind your back). You are quickly going to
>> notice that your performance is abysmal.
> 
>  I don't see any real problems, at least with LPI tables. If the guest changes something, it will be
> immediately available to us. I don't see any need to seriously validate something, at least here.
> Pending bit is just pending bit, and configuration is just priority value plus enable bit.
>  But, well, if we think a bit better, in case of pending bit modification, the operations on both
> guest and host side have to be atomic, otherwise we can clobber our table if, for example, both host
> and guest modify adjacent bits. And there's no way to interlock with the guest. So, OK, i accept
> your point.

The pending table is the least of our concerns. Device table, ITTs,
collections. That's the real problem.

	M.
-- 
Jazz is not dead. It just smells funny...