Messages in this thread | | | Date | Mon, 12 Apr 2010 12:08:15 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH 2/6] KVM MMU: fix kvm_mmu_zap_page() and its calling path |
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On 04/12/2010 11:53 AM, Xiao Guangrong wrote: >> >>> kvm->arch.n_free_mmu_pages = 0; >>> @@ -1589,7 +1589,8 @@ static void mmu_unshadow(struct kvm *kvm, gfn_t >>> gfn) >>> && !sp->role.invalid) { >>> pgprintk("%s: zap %lx %x\n", >>> __func__, gfn, sp->role.word); >>> - kvm_mmu_zap_page(kvm, sp); >>> + if (kvm_mmu_zap_page(kvm, sp)) >>> + nn = bucket->first; >>> } >>> } >>> >>> >> I don't understand why this is needed. >> > There is the code segment in mmu_unshadow(): > > |hlist_for_each_entry_safe(sp, node, nn, bucket, hash_link) { > | if (sp->gfn == gfn&& !sp->role.direct > | && !sp->role.invalid) { > | pgprintk("%s: zap %lx %x\n", > | __func__, gfn, sp->role.word); > | kvm_mmu_zap_page(kvm, sp); > | } > | } > > in the loop, if nn is zapped, hlist_for_each_entry_safe() access nn will > cause crash. and it's checked in other functions, such as kvm_mmu_zap_all(), > kvm_mmu_unprotect_page()... >
hlist_for_each_entry_safe() is supposed to be be safe against removal of the element that is pointed to by the iteration cursor.
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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