Re: [PATCH v2 1/3] kvm: svm: Add support for additional SVM NPF error codes

[Brijesh Singh]

Hi Paolo,

On 08/04/2017 09:05 AM, Paolo Bonzini wrote:
> On 04/08/2017 02:30, Brijesh Singh wrote:
> > On 8/2/17 5:42 AM, Paolo Bonzini wrote:
> > > On 01/08/2017 15:36, Brijesh Singh wrote:
> > > > > The flow is:
> > > > >
> > > > >     hardware walks page table; L2 page table points to read only memory
> > > > >     -> pf_interception (code =
> > > > >     -> kvm_handle_page_fault (need_unprotect = false)
> > > > >     -> kvm_mmu_page_fault
> > > > >     -> paging64_page_fault (for example)
> > > > >        -> try_async_pf
> > > > >           map_writable set to false
> > > > >        -> paging64_fetch(write_fault = true, map_writable = false,
> > > > > prefault = false)
> > > > >           -> mmu_set_spte(speculative = false, host_writable = false,
> > > > > write_fault = true)
> > > > >              -> set_spte
> > > > >                 mmu_need_write_protect returns true
> > > > >                 return true
> > > > >              write_fault == true -> set emulate = true
> > > > >              return true
> > > > >           return true
> > > > >        return true
> > > > >     emulate
> > > > >
> > > > > Without this patch, emulation would have called
> > > > >
> > > > >     ..._gva_to_gpa_nested
> > > > >     -> translate_nested_gpa
> > > > >     -> paging64_gva_to_gpa
> > > > >     -> paging64_walk_addr
> > > > >     -> paging64_walk_addr_generic
> > > > >        set fault (nested_page_fault=true)
> > > > >
> > > > > and then:
> > > > >
> > > > >      kvm_propagate_fault
> > > > >      -> nested_svm_inject_npf_exit
> > > > maybe then safer thing would be to qualify the new error_code check with
> > > > !mmu_is_nested(vcpu) or something like that. So that way it would run on
> > > > L1 guest, and not the L2 guest. I believe that would restrict it avoid
> > > > hitting this case. Are you okay with this change ?
> > > Or check "vcpu->arch.mmu.direct_map"?  That would be true when not using
> > > shadow pages.
> >
> > Yes that can be used.
>
> Are you going to send a patch for this?

Yes. I should be posting it by Monday or Tuesday - need sometime to verify it.

-Brijesh