Re: [Qemu-devel] vhost, iova, and dirty page tracking

[Jason Wang]

On 2019/9/18 下午4:37, Tian, Kevin wrote:
> > From: Jason Wang [mailto:address@hidden]
> > Sent: Wednesday, September 18, 2019 2:10 PM
> >
> > > > Note that the HVA to GPA mapping is not an 1:1 mapping. One HVA
> > range
> > > > could be mapped to several GPA ranges.
> > > This is fine. Currently vfio_dma maintains IOVA->HVA mapping.
> > >
> > > btw under what condition HVA->GPA is not 1:1 mapping? I didn't realize it.
> >
> > I don't remember the details e.g memory region alias? And neither kvm
> > nor kvm API does forbid this if my memory is correct.
> I checked https://qemu.weilnetz.de/doc/devel/memory.html, which
> provides an example of aliased layout. However, its aliasing is all
> 1:1, instead of N:1. From guest p.o.v every writable GPA implies an
> unique location. Why would we hit the situation where multiple
> write-able GPAs are mapped to the same HVA (i.e. same physical
> memory location)?


I don't know, just want to say current API does not forbid this. So we 
probably need to take care it.


> Is Qemu doing its own same-content memory
> merging in GPA level, similar to KSM?


AFAIK, it doesn't.

Thanks


> Thanks
> Kevin