Re: [XEN PATCH v1 1/1] Invalidate cache for cpus affinitized to the domain

["Shamsundara Havanur, Harsha" <havanur@amazon.com>]

On Mon, 2020-12-14 at 09:52 +0100, Jan Beulich wrote:
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> On 11.12.2020 12:44, Harsha Shamsundara Havanur wrote:
> > A HVM domain flushes cache on all the cpus using
> > `flush_all` macro which uses cpu_online_map, during
> > i) creation of a new domain
> > ii) when device-model op is performed
> > iii) when domain is destructed.
> > 
> > This triggers IPI on all the cpus, thus affecting other
> > domains that are pinned to different pcpus. This patch
> > restricts cache flush to the set of cpus affinitized to
> > the current domain using `domain->dirty_cpumask`.
> 
> But then you need to effect cache flushing when a CPU gets
> taken out of domain->dirty_cpumask. I don't think you/we want
> to do that.
> 
If we do not restrict, it could lead to DoS attack, where a malicious
guest could keep writing to MTRR registers or do a cache flush through
DM Op and keep sending IPIs to other neighboring guests.

-Harsha
> Jan
>