Re: [PATCH 09/11] KVM: MMU: simplify mmu_need_write_protect

[Kai Huang]

On 12/15/2015 04:43 PM, Kai Huang wrote:
> On 12/01/2015 02:26 AM, Xiao Guangrong wrote:
> > Now, all non-leaf shadow page are page tracked, if gfn is not tracked
> > there is no non-leaf shadow page of gfn is existed, we can directly
> > make the shadow page of gfn to unsync
> >
> > Signed-off-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/kvm/mmu.c | 26 ++++++++------------------
> >   1 file changed, 8 insertions(+), 18 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> > index 5a2ca73..f89e77f 100644
> > --- a/arch/x86/kvm/mmu.c
> > +++ b/arch/x86/kvm/mmu.c
> > @@ -2461,41 +2461,31 @@ static void __kvm_unsync_page(struct kvm_vcpu 
> > *vcpu, struct kvm_mmu_page *sp)
> >       kvm_mmu_mark_parents_unsync(sp);
> >   }
> >   -static void kvm_unsync_pages(struct kvm_vcpu *vcpu,  gfn_t gfn)
> > +static bool kvm_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn,
> > +                 bool can_unsync)
> >   {
> >       struct kvm_mmu_page *s;
> >         for_each_gfn_indirect_valid_sp(vcpu->kvm, s, gfn) {
> > +        if (!can_unsync)
> > +            return true;
> How about moving this right before for_each_gfn_indirect_valid_sp? As 
> can_unsync is passed as parameter, so there's no point checking it 
> several times.
>
> A further thinking is can we move it to mmu_need_write_protect? 
> Passing can_unsync as parameter to kvm_unsync_pages sounds a little 
> bit odd.
>
> > +
> >           if (s->unsync)
> >               continue;
> >           WARN_ON(s->role.level != PT_PAGE_TABLE_LEVEL);
> How about large page mapping? Such as if guest uses 2M mapping and its 
> shadow is indirect, does above WARN_ON still meet? As you removed the 
> PT level check in mmu_need_write_protect.
>
> Thanks,
> -Kai
Btw I also think this patch can be merged with patch 6.

Thanks,
-Kai
> >           __kvm_unsync_page(vcpu, s);
> >       }
> > +
> > +    return false;
> >   }
>
> >     static bool mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
> >                      bool can_unsync)
> >   {
> > -    struct kvm_mmu_page *s;
> > -    bool need_unsync = false;
> > -
> >       if (kvm_page_track_check_mode(vcpu, gfn, KVM_PAGE_TRACK_WRITE))
> >           return true;
> >   -    for_each_gfn_indirect_valid_sp(vcpu->kvm, s, gfn) {
> > -        if (!can_unsync)
> > -            return true;
> > -
> > -        if (s->role.level != PT_PAGE_TABLE_LEVEL)
> > -            return true;
> > -
> > -        if (!s->unsync)
> > -            need_unsync = true;
> > -    }
> > -    if (need_unsync)
> > -        kvm_unsync_pages(vcpu, gfn);
> > -
> > -    return false;
> > +    return kvm_unsync_pages(vcpu, gfn, can_unsync);
> >   }
> >     static bool kvm_is_mmio_pfn(pfn_t pfn)
>
> --
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