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    SubjectRe: [PATCH v3 01/11] KVM: MMU: avoid pte_list_desc running out in kvm_mmu_pte_write
    On 09/13/2011 05:51 PM, Avi Kivity wrote:
    > On 08/30/2011 05:34 AM, Xiao Guangrong wrote:
    >> kvm_mmu_pte_write is unsafe since we need to alloc pte_list_desc in the
    >> function when spte is prefetched, unfortunately, we can not know how many
    >> spte need to be prefetched on this path, that means we can use out of the
    >> free pte_list_desc object in the cache, and BUG_ON() is triggered, also some
    >> path does not fill the cache, such as INS instruction emulated that does not
    >> trigger page fault
    >>
    >> @@ -3716,10 +3735,6 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code,
    >> goto out;
    >> }
    >>
    >> - r = mmu_topup_memory_caches(vcpu);
    >> - if (r)
    >> - goto out;
    >> -
    >> er = x86_emulate_instruction(vcpu, cr2, 0, insn, insn_len);
    >>
    >
    > Suppose we are out of memory, can't this get us in an endless loop?
    >
    > return -ENOMEM breaks as out (and kills the guest, likely).
    >

    If memory is not enough, we just clear sptes on pte_write path(not prefetch spte),
    the later page fault path can return -1 to let guest crash. Hmm?



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