Re: [PATCH v4 06/17] KVM: x86/mmu: Allocate DPAMT pages for vCPU-induced page split

[Yan Zhao]

On Sat, Oct 10, 2026 at 02:37:17PM +0800, Yan Zhao wrote:
> On Wed, Oct 07, 2026 at 11:45:48PM +0800, Edgecombe, Rick P wrote:
> > On Mon, 2026-09-28 at 17:10 +0800, Yan Zhao wrote:
> > > From: Sean Christopherson <seanjc@xxxxxxxxxx>
> > > 
> > > Extend the TDP MMU to allocate Dynamic PAMT backing pages (DPAMT pages) for
> > > vCPU-induced huge page splits in mirror roots when DPAMT is enabled.
> > > 
> > > Leverage the .topup_external_cache() interface to topup the DPAMT cache
> > > when allocating a new child page table for splitting. The DPAMT cache is
> > > currently a per-vCPU thread-local list. When a vCPU-induced page split
> > > occurs, DPAMT pages can be drawn locklessly from the list.
> > > 
> > > Pass min_nr_spts as 1 to .topup_external_cache(), indicating there's one
> > > new S-EPT page table page. So, tdx_topup_external_pamt_cache() will
> > > allocate DPAMT page pairs for both the newly added S-EPT page table page
> > > and the demoted guest private page.
> > > 
> > > tdp_mmu_alloc_sp_for_split() is currently not reachable from a non-vCPU
> > > context for mirror roots, since dirty page tracking is not yet allowed on
> > > mirror roots. So, simply add a WARN if tdx_topup_external_pamt_cache() is
> > > invoked under a non-vCPU context.
> > > 
> > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > > Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
> > > ---
> > > v4: new patch.
> > 
> > New? It is essentially this with a new log, right?
> > https://lore.kernel.org/kvm/20260129011517.3545883-39-seanjc@xxxxxxxxxx/#t
> Ha, "new patch" is relative to v3.
> It's indeed introduced by Sean from the DPAMT combined v5.
Let me add a Link to Sean's original post in the next version.

> > Reviewed-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> > 
> > 
> >