Re: [PATCH v2] KVM: Ignore MMU notifiers for guest_memfd-only memslots

[Sean Christopherson <seanjc@google.com>]

On Tue, Jul 14, 2026, Alexandru Elisei wrote:
> +	 * TODO: Skip gmem-only memslots on mmu_notifier events entirely, once
> +	 * gfn_to_pfn_cache is also wired up to directly pull from guest_memfd.

So it turns out we need to solve a very related problem[*], thanks to commit
b9220d32799a ("KVM: x86/xen: allow shared_info to be mapped by fixed HVA"),
which as it says, allows populating gfn_to_pfn_cache directly with an HVA, i.e.
without a memslot.

My not-yet-tested solution for that mess is to give gfn_to_pfn_cache its own
invalidation sequence, at which point there shouldn't be a need to process
gmem-only memslots just for gfn_to_pfn_cache, because it will already be equipped
to handle memslot-less invalidation.

Given how simple this change *should* be, I'm going to put this patch on the
backburner for now, and then assuming my proposed change actually works, I'll
grab your original change (or more likely, re-post it as the last patch in the
series weans gfn_to_pfn_cache off mmu_invalidate_seq).

It'll probably take me a few weeks to circle back to this, as I finally crawled
out from underneath a pile of urgent and am just now getting back into review
mode, but this is fairly high on my todo list, so with luck we might still squeeze
this into 7.3.

[*] https://lore.kernel.org/all/aj2hi-NcqUUCaoQF@google.com