Re: [PATCH v4] kvm: Fix page ageing bugs

[Wanpeng Li]

Hi Paolo,
ä 9/24/14, 3:04 PM, Paolo Bonzini åé:
> Il 24/09/2014 04:27, Wanpeng Li ha scritto:
> > Hi Andres,
> > On Mon, Sep 22, 2014 at 02:54:42PM -0700, Andres Lagar-Cavilla wrote:
> > > 1. We were calling clear_flush_young_notify in unmap_one, but we are
> > > within an mmu notifier invalidate range scope. The spte exists no more
> > > (due to range_start) and the accessed bit info has already been
> > > propagated (due to kvm_pfn_set_accessed). Simply call
> > > clear_flush_young.
> > >
> > > 2. We clear_flush_young on a primary MMU PMD, but this may be mapped
> > > as a collection of PTEs by the secondary MMU (e.g. during log-dirty).
> > > This required expanding the interface of the clear_flush_young mmu
> > > notifier, so a lot of code has been trivially touched.
> > >
> > > 3. In the absence of shadow_accessed_mask (e.g. EPT A bit), we emulate
> > > the access bit by blowing the spte. This requires proper synchronizing
> > > with MMU notifier consumers, like every other removal of spte's does.
> > [...]
> > > ---
> > > +	BUG_ON(!shadow_accessed_mask);
> > >
> > > 	for (sptep = rmap_get_first(*rmapp, &iter); sptep;
> > > 	     sptep = rmap_get_next(&iter)) {
> > > +		struct kvm_mmu_page *sp;
> > > +		gfn_t gfn;
> > > 		BUG_ON(!is_shadow_present_pte(*sptep));
> > > +		/* From spte to gfn. */
> > > +		sp = page_header(__pa(sptep));
> > > +		gfn = kvm_mmu_page_get_gfn(sp, sptep - sp->spt);
> > >
> > > 		if (*sptep & shadow_accessed_mask) {
> > > 			young = 1;
> > > 			clear_bit((ffs(shadow_accessed_mask) - 1),
> > > 				 (unsigned long *)sptep);
> > > 		}
> > > +		trace_kvm_age_page(gfn, slot, young);
> > IIUC, all the rmapps in this for loop are against the same gfn which
> > results in the above trace point dump the message duplicated.
> You're right; Andres's patch "[PATCH] kvm/x86/mmu: Pass gfn and level to
> rmapp callback" helps avoiding that.

From Andres's patch "[PATCH] kvm/x86/mmu: Pass gfn and level to rmapp 
callback"

@@ -1410,25 +1421,20 @@ static int kvm_age_rmapp(struct kvm *kvm, 
unsigned long *rmapp,

for (sptep = rmap_get_first(*rmapp, &iter); sptep;
sptep = rmap_get_next(&iter)) {
- struct kvm_mmu_page *sp;
- gfn_t gfn;
BUG_ON(!is_shadow_present_pte(*sptep));
- /* From spte to gfn. */
- sp = page_header(__pa(sptep));
- gfn = kvm_mmu_page_get_gfn(sp, sptep - sp->spt);
-
if (*sptep & shadow_accessed_mask) {
young = 1;
clear_bit((ffs(shadow_accessed_mask) - 1),
(unsigned long *)sptep);
}
- trace_kvm_age_page(gfn, slot, young);
+ trace_kvm_age_page(gfn, level, slot, young);
}
return young;
}


This trace point still dup duplicated message for the same gfn in the 
for loop.

Regards,
Wanpeng Li

> Paolo
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