Re: [PATCH 11/11] KVM: MMU: improve write flooding detected

Avi Kivity
2011-08-25T14:07:46Z

On 08/25/2011 04:21 PM, Marcelo Tosatti wrote:
> On Thu, Aug 25, 2011 at 07:42:10AM +0300, Avi Kivity wrote:
> > On 08/25/2011 05:04 AM, Marcelo Tosatti wrote:
> > >>
> > >> It could increase the flood count independently of the accessed bit of
> > >> the spte being updated, zapping after 3 attempts as it is now.
> > >>
> > >> But additionally reset the flood count if the gpte appears to be valid
> > >> (points to an existant gfn if the present bit is set, or if its zeroed).
> > >
> > >Well not zero, as thats a common pattern for non ptes.
> > >
> >
> > On 32-bit with 4GB RAM, practically anything is a valid gpte.
>
> The following could be required to consider a valid gpte, for write
> flood detection purposes:
>
> - Must be present.
> - PageCacheDisable must be unset.
> - PageWriteThrough must be unset.
>

Unless the guest is using PAT.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.