Re: [RFC, PATCH 05/12] KVM: TDX: Add tdx_pamt_get()/put() helpers

[Yan Zhao <yan.y.zhao@intel.com>]

On Tue, May 06, 2025 at 06:15:40PM -0700, Vishal Annapurve wrote:
> On Tue, May 6, 2025 at 6:04 PM Yan Zhao <yan.y.zhao@intel.com> wrote:
> >
> > On Mon, May 05, 2025 at 08:44:26PM +0800, Huang, Kai wrote:
> > > On Fri, 2025-05-02 at 16:08 +0300, Kirill A. Shutemov wrote:
> > > > +static int tdx_pamt_add(atomic_t *pamt_refcount, unsigned long hpa,
> > > > +                   struct list_head *pamt_pages)
> > > > +{
> > > > +   u64 err;
> > > > +
> > > > +   hpa = ALIGN_DOWN(hpa, SZ_2M);
> > > > +
> > > > +   spin_lock(&pamt_lock);
> > >
> > > Just curious, Can the lock be per-2M-range?
> > Me too.
> > Could we introduce smaller locks each covering a 2M range?
> >
> > And could we deposit 2 pamt pages per-2M hpa range no matter if it's finally
> > mapped as a huge page or not?
> >
> 
> Are you suggesting to keep 2 PAMT pages allocated for each private 2M
> page even if it's mapped as a hugepage? It will lead to wastage of
> memory of 4 MB per 1GB of guest memory range. For large VM sizes that
> will amount to high values.
Ok. I'm thinking of the possibility to aligning the time of PAMT page allocation
to that of physical page allocation.