Re: [PATCH] KVM: VMX: Execute WBINVD to keep data consistency with assigned devices

[Sheng Yang <sheng@linux.intel.com>]

On Friday 25 June 2010 16:54:19 Jan Kiszka wrote:
> Sheng Yang wrote:
> > Some guest device driver may leverage the "Non-Snoop" I/O, and explicitly
> > WBINVD or CLFLUSH to a RAM space. Since migration may occur before WBINVD
> > or CLFLUSH, we need to maintain data consistency either by:
> > 1: flushing cache (wbinvd) when the guest is scheduled out if there is no
> > wbinvd exit, or
> > 2: execute wbinvd on all dirty physical CPUs when guest wbinvd exits.
> > 
> > For wbinvd VMExit capable processors, we issue IPIs to all physical CPUs
> > to do wbinvd, for we can't easily tell which physical CPUs are "dirty".
> 
> wbinvd is a heavy weapon in the hands of a guest. Even if it is limited
> to pass-through scenarios, do we really need to bother all physical host
> CPUs with potential multi-millisecond stalls? Think of VMs only running
> on a subset of CPUs (e.g. to isolate latency sources). I would suggest
> to track the physical CPU usage of VCPUs between two wbinvd requests and
> only send the wbinvd IPI to that set.

OK, would try to make it more specific(and complex)...
> 
> Also, I think the code is still too much vmx-focused. Only the trapping
> should be vendor specific, the rest generic.

OK, would consider it.

--
regards
Yang, Sheng

> 
> Jan