KVM: x86/mmu: Retry page fault if root is invalidated by memslot update
Bail from the page fault handler if the root shadow page was obsoleted by a memslot update. Do the check _after_ acuiring mmu_lock, as the TDP MMU doesn't rely on the memslot/MMU generation, and instead relies on the root being explicit marked invalid by kvm_mmu_zap_all_fast(), which takes mmu_lock for write. For the TDP MMU, inserting a SPTE into an obsolete root can leak a SP if kvm_tdp_mmu_zap_invalidated_roots() has already zapped the SP, i.e. has moved past the gfn associated with the SP. For other MMUs, the resulting behavior is far more convoluted, though unlikely to be truly problematic. Installing SPs/SPTEs into the obsolete root isn't directly problematic, as the obsolete root will be unloaded and dropped before the vCPU re-enters the guest. But because the legacy MMU tracks shadow pages by their role, any SP created by the fault can can be reused in the new post-reload root. Again, that _shouldn't_ be problematic as any leaf child SPTEs will be created for the current/valid memslot generation, and kvm_mmu_get_page() will not reuse child SPs from the old generation as they will be flagged as obsolete. But, given that continuing with the fault is pointess (the root will be unloaded), apply the check to all MMUs. Fixes: b7cccd39 ("KVM: x86/mmu: Fast invalidation for TDP MMU") Cc: stable@vger.kernel.org Cc: Ben Gardon <bgardon@google.com> Signed-off-by:Sean Christopherson <seanjc@google.com> Message-Id: <20211120045046.3940942-5-seanjc@google.com> Signed-off-by:
Paolo Bonzini <pbonzini@redhat.com>
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