Re: [RFC PATCH v2 24/26] KVM: arm64: Make memcache anonymous in pgtable allocator

[Will Deacon]

On Thu, Feb 04, 2021 at 02:24:44PM +0000, Quentin Perret wrote:
> On Wednesday 03 Feb 2021 at 15:59:44 (+0000), Will Deacon wrote:
> > On Fri, Jan 08, 2021 at 12:15:22PM +0000, Quentin Perret wrote:
> > > The current stage2 page-table allocator uses a memcache to get
> > > pre-allocated pages when it needs any. To allow re-using this code at
> > > EL2 which uses a concept of memory pools, make the memcache argument to
> > > kvm_pgtable_stage2_map() anonymous. and let the mm_ops zalloc_page()
> > > callbacks use it the way they need to.
> > > 
> > > Signed-off-by: Quentin Perret <qperret@xxxxxxxxxx>
> > > ---
> > >  arch/arm64/include/asm/kvm_pgtable.h | 6 +++---
> > >  arch/arm64/kvm/hyp/pgtable.c         | 4 ++--
> > >  2 files changed, 5 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> > > index 8e8f1d2c5e0e..d846bc3d3b77 100644
> > > --- a/arch/arm64/include/asm/kvm_pgtable.h
> > > +++ b/arch/arm64/include/asm/kvm_pgtable.h
> > > @@ -176,8 +176,8 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt);
> > >   * @size:	Size of the mapping.
> > >   * @phys:	Physical address of the memory to map.
> > >   * @prot:	Permissions and attributes for the mapping.
> > > - * @mc:		Cache of pre-allocated GFP_PGTABLE_USER memory from which to
> > > - *		allocate page-table pages.
> > > + * @mc:		Cache of pre-allocated memory from which to allocate page-table
> > > + *		pages.
> > 
> > We should probably mention that this memory must be zeroed, since I don't
> > think the page-table code takes care of that.
> 
> OK, though I think this is unrelated to this change -- this is already
> true today I believe. Anyhow, I'll pile a change on top.

It is, but GFP_PGTABLE_USER implies __GFP_ZERO, so the existing comment
captures that.

Will