Messages in this thread | | | Date | Tue, 29 Jun 2010 10:06:38 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH v2 3/10] KVM: MMU: fix direct sp's access corruptted |
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On 06/29/2010 04:17 AM, Xiao Guangrong wrote: > >> If B is writeable-and-dirty, then it's D bit is already set, and we >> don't need to do anything. >> >> If B is writeable-and-clean, then we'll have an spte pointing to a >> read-only sp, so we'll get a write fault on access and an opportunity to >> set the D bit. >> >> > Sorry, a typo in my reply, i mean mapping A and B both are writable-and-clean, > while A occurs write-#PF, we should change A's spte map to writable sp, if we > only update the spte in writable-and-clean sp(form readonly to writable), the B's > D bit will miss set. >
Right.
We need to update something to notice this:
- FNAME(fetch)() to replace the spte - FNAME(walk_addr)() to invalidate the spte
I think FNAME(walk_addr) is the right place, we're updating the gpte, so we should update the spte at the same time, just like a guest write. But that will be expensive (there could be many sptes, so we have to call kvm_mmu_pte_write()), so perhaps FNAME(fetch) is easier.
We have now
if (is_shadow_present_pte(*sptep) && !is_large_pte(*sptep)) continue;
So we need to add a check, if sp->role.access doesn't match pt_access & pte_access, we need to get a new sp with the correct access (can only change read->write).
>>> Anyway, i think we should re-intall the mapping when the state is >>> changed. :-( >>> >>> >> When the gpte is changed from read-only to writeable or from clean to >> dirty, we need to update the spte, yes. But that's true for other sptes >> as well, not just large gptes. >> >> > I think the indirect sp is not hurt by this bug since for the indirect sp, the access > just form its upper-level, and the D bit is only in the last level, when we change the > pte's access, is not affect its sp's access. > > But for direct sp, the sp's access is form all level. and different mapping that not share > the last mapping page will have the same last sp. >
Right.
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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