Messages in this thread | | | From | Paolo Bonzini <> | Subject | Re: [PATCH 09/54] KVM: x86/mmu: Unconditionally zap unsync SPs when creating >4k SP at GFN | Date | Wed, 23 Jun 2021 18:38:33 +0200 |
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On 23/06/21 17:08, Sean Christopherson wrote: > Because the shadow page's level is incorporated into its role, if the level of > the new page is >4k, the branch at (1) will be taken for all 4k shadow pages. > > Maybe something like this for a comment?
Good, integrated.
Though I also wonder why breaking out of the loop early is okay. Initially I thought that zapping only matters if there's no existing page with the desired role, because otherwise the unsync page would have been zapped already by an earlier kvm_get_mmu_page, but what if the page was synced at the time of kvm_get_mmu_page and then both were unsynced?
It may be easier to just split the loop to avoid that additional confusion, something like:
/* * If the guest is creating an upper-level page, zap unsync pages * for the same gfn, because the gfn will be write protected and * future syncs of those unsync pages could happen with an incompatible * context. While it's possible the guest is using recursive page * tables, in all likelihood the guest has stopped using the unsync * page and is installing a completely unrelated page. */ if (level > PG_LEVEL_4K) { for_each_valid_sp(vcpu->kvm, sp, sp_list) if (sp->gfn == gfn && sp->role.word != role.word && sp->unsync) kvm_mmu_prepare_zap_page(vcpu->kvm, sp, &invalid_list); }
Paolo
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