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Date: Mon, 8 Nov 2010 19:01:36 +0200 From: Gleb Natapov <gleb@...hat.com> To: Xiao Guangrong <xiaoguangrong.eric@...il.com> Cc: Xiao Guangrong <xiaoguangrong@...fujitsu.com>, Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>, LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org> Subject: Re: [PATCH 2/3] KVM: MMU: don not retry #PF for nonpaging guest On Tue, Nov 09, 2010 at 12:58:24AM +0800, Xiao Guangrong wrote: > 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. > No A-apf.gva should contain L1 physical address. > On 11/8/10, Gleb Natapov <gleb@...hat.com> 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@...r.kernel.org > > 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 -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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