Re: [PATCH 6/6] KVM: MMU: fast zap all shadow pages

From: Xiao Guangrong
Date: Tue Mar 19 2013 - 11:37:57 EST

On 03/19/2013 10:40 PM, Marcelo Tosatti wrote:

> I misunderstood the benefit of your idea (now i got it: zap root
> and flush TLB guarantees vcpus will refault). What i'd like to avoid is
> memset(cache, 0, sizeof(*cache));
> kvm_mmu_init(kvm);
> I'd prefer normal operations on those data structures (in mmu_cache).
> And also the page accounting is a problem.
> Perhaps you can use a generation number to consider whether shadow pages
> are valid? So:
> find_sp(gfn_t gfn)
> lookup hash
> if sp->generation_number != mmu->current_generation_number
> initialize page as if it were just allocated (but keep it in the hash list)
> And on kvm_mmu_zap_all()
> spin_lock(mmu_lock)
> for each page
> if page->root_count
> zero sp->spt[]
> flush TLB
> mmu->current_generation_number++
> spin_unlock(mmu_lock)
> Then have kvm_mmu_free_all() that actually frees all data.
> Hum, not sure if thats any better than your current patchset.

I also got the idea of generation number like yours which i mentioned
it in the [PATCH 0/6]:

Avoiding Marcelo beat me :), they are some works not attached to make the
patchset more smaller:
(1): batch kvm_reload_remote_mmus for zapping root shadow pages
(2): free shadow pages by using generation-number
(3): remove unneeded kvm_reload_remote_mmus after kvm_mmu_zap_all
(4): drop unnecessary @npages from kvm_arch_create_memslot
(5): rename init_kvm_mmu to init_vcpu_mmu

> Well, maybe resend patchset with bug fixes / improvements and
> we go from there.

I agree. Thanks for your time, Marcelo!

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