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SubjectRe: [PATCH 0/4] KVM: x86/mmu: Zap invalid TDP MMU roots when unmapping
On Wed, Dec 15, 2021, Paolo Bonzini wrote:
> On 12/15/21 02:15, Sean Christopherson wrote:
> > Patches 01-03 implement a bug fix by ensuring KVM zaps both valid and
> > invalid roots when unmapping a gfn range (including the magic "all" range).
> > Failure to zap invalid roots means KVM doesn't honor the mmu_notifier's
> > requirement that all references are dropped.
> >
> > set_nx_huge_pages() is the most blatant offender, as it doesn't elevate
> > mm_users and so a VM's entire mm can be released, but the same underlying
> > bug exists for any "unmap" command from the mmu_notifier in combination
> > with a memslot update. E.g. if KVM is deleting a memslot, and a
> > mmu_notifier hook acquires mmu_lock while it's dropped by
> > kvm_mmu_zap_all_fast(), the mmu_notifier hook will see the to-be-deleted
> > memslot but won't zap entries from the invalid roots.
> >
> > Patch 04 is cleanup to reuse the common iterator for walking _only_
> > invalid roots.
> >
> > Sean Christopherson (4):
> > KVM: x86/mmu: Use common TDP MMU zap helper for MMU notifier unmap
> > hook
> > KVM: x86/mmu: Move "invalid" check out of kvm_tdp_mmu_get_root()
> > KVM: x86/mmu: Zap _all_ roots when unmapping gfn range in TDP MMU
> > KVM: x86/mmu: Use common iterator for walking invalid TDP MMU roots
> >
> > arch/x86/kvm/mmu/tdp_mmu.c | 116 +++++++++++++++++--------------------
> > arch/x86/kvm/mmu/tdp_mmu.h | 3 -
> > 2 files changed, 53 insertions(+), 66 deletions(-)
> >
>
> Queued 1-3 for 5.16 and 4 for 5.17.

Actually, can you please unqueue patch 4? I think we can actually kill off
kvm_tdp_mmu_zap_invalidated_roots() entirely. I don't know if that code will be
ready for 5.17, but if it is then this patch is unnecesary. And if not, it
shouldn't be difficult to re-queue this a bit later.

Thanks!

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