Re: [PATCH v2 2/2] KVM: PPC: Book3S HV: rework secure mem slot dropping

[Laurent Dufour]

Le 21/07/2020 Ã 23:37, Ram Pai a ÃcritÂ:
> On Tue, Jul 21, 2020 at 12:42:02PM +0200, Laurent Dufour wrote:
> > When a secure memslot is dropped, all the pages backed in the secure device
> > (aka really backed by secure memory by the Ultravisor) should be paged out
> > to a normal page. Previously, this was achieved by triggering the page
> > fault mechanism which is calling kvmppc_svm_page_out() on each pages.
> >
> > This can't work when hot unplugging a memory slot because the memory slot
> > is flagged as invalid and gfn_to_pfn() is then not trying to access the
> > page, so the page fault mechanism is not triggered.
> >
> > Since the final goal is to make a call to kvmppc_svm_page_out() it seems
> > simpler to directly calling it instead of triggering such a mechanism. This
>              ^^ call directly instead of triggering..
>
> > way kvmppc_uvmem_drop_pages() can be called even when hot unplugging a
> > memslot.
> >
> > Since kvmppc_uvmem_drop_pages() is already holding kvm->arch.uvmem_lock,
> > the call to __kvmppc_svm_page_out() is made.
> > As __kvmppc_svm_page_out needs the vma pointer to migrate the pages, the
> > VMA is fetched in a lazy way, to not trigger find_vma() all the time. In
> > addition, the mmap_sem is help in read mode during that time, not in write
> 		          ^^ held
>
> > mode since the virual memory layout is not impacted, and
> > kvm->arch.uvmem_lock prevents concurrent operation on the secure device.
> >
> > Cc: Ram Pai <linuxram@xxxxxxxxxx>
>
> Reviewed-by: Ram Pai <linuxram@xxxxxxxxxx>

Thanks for reviewing this series.

Regarding the wordsmithing, Paul, could you manage that when pulling the series?

Thanks,
Laurent.