Re: H_CLEAR_REF and H_CLEAR_MOD

[Paul Mackerras <paulus@samba.org>]

On Sat, Apr 11, 2015 at 12:57:54PM -0700, Nathan Whitehorn wrote:
> 
> 
> On 02/18/15 15:33, Nathan Whitehorn wrote:
> >
> >On 02/18/15 14:00, Paul Mackerras wrote:
> >>On Wed, Feb 18, 2015 at 09:34:54AM +0100, Alexander Graf wrote:
> >>>>Am 18.02.2015 um 07:12 schrieb Nathan Whitehorn
> >>>><nwhitehorn@freebsd.org>:
> >>>>
> >>>>It seems like KVM doesn't implement the H_CLEAR_REF and H_CLEAR_MOD
> >>>>hypervisor calls, which are absolutely critical for memory
> >>>>management in the FreeBSD kernel (and are marked "mandatory" in the
> >>>>PAPR manual). It seems some patches have been contributed already in https://lists.ozlabs.org/pipermail/linuxppc-dev/2011-December/095013.html,
> >>>>so it would be fantastic if these could end up upstream.
> >>>Paul, I guess we never included this because  there was no user. If
> >>>FreeBSD does use it though, I think it makes a lot of sense to resend
> >>>it for inclusion.
> >>I agree.  I just need to check the locking and synchronization around
> >>the reference and change bit recording, then I'll resend it.
> >
> >Thanks much! Please let me know if I can help at all with this.
> 
> Any news on this? I'm happy to test the patch if you like.
> -Nathan

I have discovered a bug where we can lose the host-side view of the
dirtiness of pages when the guest does a H_CLEAR_MOD on a huge-page
HPTE, so I'm working on a fix for that.

Paul.