CVE-2021-47094CVE-2021-47094

In the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Don't advance iterator after restart due to yielding After dropping mmu_lock in the TDP MMU, restart the iterator during tdp_iter_next() and do not advance the iterator. Advancing the iterator results in skipping the top-level SPTE and all its children, which is fatal if any of the skipped SPTEs were not visited before yielding. When zapping all SPTEs, i.e. when min_level == root_level, restarting the iter and then invoking tdp_iter_next() is always fatal if the current gfn has as a valid SPTE, as advancing the iterator results in try_step_side() skipping the current gfn, which wasn't visited before yielding. Sprinkle WARNs on iter->yielded being true in various helpers that are often used in conjunction with yielding, and tag the helper with __must_check to reduce the probabily of improper usage. Failing to zap a top-level SPTE manifests in one of two ways. If a valid SPTE is skipped by both kvm_t