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SubjectRe: [PATCH 08/11] KVM: MMU: use page track for non-leaf shadow pages
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On 12/15/2015 05:10 PM, Xiao Guangrong wrote:
>
>
> On 12/15/2015 03:52 PM, Kai Huang wrote:
>
>>> static bool __mmu_gfn_lpage_is_disallowed(gfn_t gfn, int level,
>>> @@ -2140,12 +2150,18 @@ static struct kvm_mmu_page
>>> *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
>>> hlist_add_head(&sp->hash_link,
>>> &vcpu->kvm->arch.mmu_page_hash[kvm_page_table_hashfn(gfn)]);
>>> if (!direct) {
>>> - if (rmap_write_protect(vcpu, gfn))
>>> + /*
>>> + * we should do write protection before syncing pages
>>> + * otherwise the content of the synced shadow page may
>>> + * be inconsistent with guest page table.
>>> + */
>>> + account_shadowed(vcpu->kvm, sp);
>>> +
>>> + if (level == PT_PAGE_TABLE_LEVEL &&
>>> + rmap_write_protect(vcpu, gfn))
>>> kvm_flush_remote_tlbs(vcpu->kvm);
>> I think your modification is good but I am little bit confused here.
>> In account_shadowed, if
>> sp->role.level > PT_PAGE_TABLE_LEVEL, the sp->gfn is write protected,
>> and this is reasonable. So why
>> write protecting the gfn of PT_PAGE_TABLE_LEVEL here?
>
> Because the shadow page will become 'sync' that means the shadow page
> will be synced
> with the page table in guest. So the shadow page need to be
> write-protected to avoid
> the guest page table is changed when we do the 'sync' thing.
>
> The shadow page need to be write-protected to avoid that guest page
> table is changed
> when we are syncing the shadow page table. See kvm_sync_pages() after
> doing
> rmap_write_protect().
I see. So why are you treat PT_PAGE_TABLE_LEVEL gfn separately here? why
this cannot be done in account_shadowed, as you did for upper level sp?
Actually I am thinking whether account_shadowed is overdoing things.
From it's name it should only *account* shadow sp, but now it also does
write protection and disable large page mapping.

Thanks,
-Kai
>
>>> /*
>>> * remove the guest page from the tracking pool which stops the
>>> interception
>>> * of corresponding access on that page. It is the opposed
>>> operation of
>>> @@ -134,20 +160,12 @@ void kvm_page_track_remove_page(struct kvm
>>> *kvm, gfn_t gfn,
>>> struct kvm_memory_slot *slot;
>>> int i;
>>> - WARN_ON(!check_mode(mode));
>>> -
>>> for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
>>> slots = __kvm_memslots(kvm, i);
>>> slot = __gfn_to_memslot(slots, gfn);
>>> spin_lock(&kvm->mmu_lock);
>>> - update_gfn_track(slot, gfn, mode, -1);
>>> -
>>> - /*
>>> - * allow large page mapping for the tracked page
>>> - * after the tracker is gone.
>>> - */
>>> - kvm_mmu_gfn_allow_lpage(slot, gfn);
>>> + kvm_slot_page_track_remove_page_nolock(kvm, slot, gfn, mode);
>> Looks you need to merge this part with patch 1, as you are modifying
>> kvm_page_track_{add,remove}_page here, which are introduced in your
>> patch 1.
>
> Indeed, it is better.
>
>



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