Messages in this thread | ![/](/images/icornerl.gif) | | Date | Fri, 5 Apr 2024 16:06:33 +0200 | Subject | Re: [RFC PATCH 0/4] KVM: x86/mmu: Rework marking folios dirty/accessed | From | Paolo Bonzini <> |
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On 4/5/24 15:59, Sean Christopherson wrote: > Ya, from commit c13fda237f08 ("KVM: Assert that notifier count is elevated in > .change_pte()"): > > x86 and MIPS are clearcut nops if the old SPTE is not-present, and that > is guaranteed due to the prior invalidation. PPC simply unmaps the SPTE, > which again should be a nop due to the invalidation. arm64 is a bit > murky, but it's also likely a nop because kvm_pgtable_stage2_map() is > called without a cache pointer, which means it will map an entry if and > only if an existing PTE was found. > > I'm 100% in favor of removing .change_pte(). As I've said multiple times, the > only reason I haven't sent a patch is because I didn't want it to prompt someone > into resurrecting the original behavior. 🙂
Ah, this indeed reminded me of discussions we had in the past. Patches sent now:
https://lore.kernel.org/kvm/20240405115815.3226315-1-pbonzini@redhat.com/
and I don't think anyone would try to resurrect the original behavior. It made some sense when there was an .invalidate_page() callback as well, but the whole thing started to crumble when .invalidate_page() was made sleepable, plus as David noticed it's very poorly documented where to use set_pte_at_notify() vs. set_pte_at().
As I wrote in the cover letter above, the only reason why it has never caused a bug is because it was doing nothing...
Paolo
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