Re: [PATCH -v2] Monitor command: pfa2hva, translate guest physical address to host virtual address

[Avi Kivity <avi@redhat.com>]

On 11/10/2010 09:16 PM, Andi Kleen wrote:
> On Wed, Nov 10, 2010 at 07:47:11PM +0200, Avi Kivity wrote:
> >  On 11/10/2010 07:44 PM, Andi Kleen wrote:
> >  >>   Doing it in userspace in easier, since we can replace the vma for
> >  >>   that section (and avoid mixed 4k/2M pages in hugetlbfs).
> >  >
> >  >You can't do that today, there's no way currently to access the non corrupted
> >  >portion of the 2MB page. Once it's poisoned it's all gone.
> >
> >  I see.  Thanks.
>
> BTW my understanding is that KVM will only use hugepages with
> transparent huge pages anyways, correct?

There will always be those who want full control over every last bit; 
they will use hugetlbfs and numactl for manual allocation of resources 
for guests.

General usage will be with transparent huge pages, though.

> So it may be reasonable to simply fix this as part of the transparent
> hugepages work, but ignore it before that.

Transparent hugepages work only for anonymous memory.

However, hugetlbfs is not the only option for backing -mempath memory; 
if poisoning works for tmpfs/shm or other file backed memory, we can use 
that to get named access to memory.

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