lkml.org 
[lkml]   [2011]   [Sep]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v3 01/11] KVM: MMU: avoid pte_list_desc running out in kvm_mmu_pte_write
    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. :-)




    \
     
     \ /
      Last update: 2011-09-13 21:31    [W:0.038 / U:1.024 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site