Re: [RFC PATCH 1/1] KVM: x86: Skip empty TDP leaf page tables

[Sean Christopherson <seanjc@google.com>]

On Fri, Aug 14, 2026, Hao Zhang wrote:
> From: Hao Zhang <zhanghao1@kylinos.cn>
> 
> When KVM zaps only leaf SPTEs, the TDP page table hierarchy is
> intentionally retained so that subsequent faults can reuse it.  However,
> a later zap of the same range still descends through retained 4K leaf
> page tables whose leaf SPTEs are all non-present.
> 
> Track whether a retained 4K leaf page table contains any present leaf
> SPTEs.  If a zap fully covers the corresponding 2MiB range and the page
> table is known to be empty, skip descending into it.
> 
> Keep the page table hierarchy linked so that it can still be reused by
> future page faults.  Installing a new leaf SPTE clears the empty hint.
> The hint checks are skipped for ranges smaller than a complete 2MiB leaf
> page table.
> 
> The iterator restarts its walk from the root after yielding.  Allow the
> restarted walk to mark an empty leaf page table again instead of
> permanently excluding the page table that contained the yield.
> 
> Tested on a 4-vCPU, 1GB guest with five repetitions on the same host.
> The main improvement is seen for repeated same-range invalidation; rolling
> sweep workloads are mostly neutral.
> 
> Signed-off-by: Hao Zhang <zhanghao1@kylinos.cn>
> ---

Does the generic iterator solution I provided a (long) while back work for your
use case?  I would still strongly prefer a generic solution that doesn't rely on
storing metadata in the MMU page.

https://lore.kernel.org/all/ZxmGdhwr9BlhUQ_Y@google.com