On 09/13/2011 06:50 PM, Avi Kivity wrote: > On 09/13/2011 01:24 PM, Xiao Guangrong wrote: >> 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? >> > > Yes. > > btw, is rmap_can_add() sufficent? We allocate more than just rmaps in mmu_topup_memory_caches(). I guess it is, but this is getting tricky. > rmap_can_add() is used to avoid prefetching sptes more than the number of rmaps in the cache, because we do not know the exact number of sptes to be fetched. :-) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
