I mean the second case, the problem is in "d:", now, A-apf is on L0->L1 mapping, and A-apf.gva is nested fault address(L2's physics address in L0->L2 mapping), you use this address to retry #pf in L0->L1 mapping? it is just waste. On 11/8/10, Gleb Natapov <gleb@xxxxxxxxxx> wrote: > On Mon, Nov 08, 2010 at 10:14:35AM +0800, Xiao Guangrong wrote: >> On 11/05/2010 06:31 PM, Gleb Natapov wrote: >> > On Fri, Nov 05, 2010 at 04:03:28PM +0800, Xiao Guangrong wrote: >> >> On 11/05/2010 03:45 PM, Gleb Natapov wrote: >> >> >> >>>> >> >>>> It looks like something broken: apfs can generated in L2 guest >> >>>> (nested ntp guest) >> >>>> and be retried in L1 guest. >> >>>> >> >>> Why is this a problem? apf will be generate on direct map even when L2 >> >>> guest is running so it should be OK to prefault it into direct map on >> >>> completion. >> >>> >> >> >> >> The nested_cr3 is different between L2 and L1, fix L2's page fault in >> >> L1's page table >> >> is useless. >> > But we are fixing L0 page faults in L0 page table. We do not start apf >> > because of L1 faulted in its page table. >> > >> >> Hi Gleb, >> >> For example, NPT Guest L1 runs on Host, and Nested NPT Guest L2 runs on >> Guest L1. >> Now, Guest L2 is running, has below sequences: >> >> a: NPF/PF occurs in L2 Guest, and generates a apf(named A-apf), then >> L2 Guest is blocked >> > What do you mean by that? Do you mean L2 exits to L1 with NPF because > L1 swapped out L2 page? In this case apf will be generated and handled > by L1 just like in L0->L1 non-nested case. Or do you mean L2 exits to L0 > with NPF because L0 swapped out L1 page? Lets assume you mean second > case since it is interesting one. > >> b: a external event wakes up L2 Guest, and let it run again. >> >> c: L2 Guest VMEXIT to L1 Guest because L2 Guest's action is intercepted by >> Guest L1 >> >> d: When cpu enter L1 Guest, A-apf is completed, then it will retry A-apf >> in >> L1 Guest's mmu context, and this 'retry' is useless. > Since A-apf was on L0->L1 mapping it is OK to prefault it into direct > map. Wen L2 will run again and try to access this page it fill fault > again since the page is not pre-faulted into nntp shadow page. This time > L0 will find page in memory and will create shadow mapping for it > without apf. > >> >> Could you please point it out for me if i missed something. :-) >> > > -- > Gleb. > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- Sent from my mobile device -- 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
