Re: [PATCH 08/11] KVM: MMU: use page track for non-leaf shadow pages

From: Kai Huang <kai.huang@linux.intel.com>
To: Xiao Guangrong <guangrong.xiao@linux.intel.com>, pbonzini@redhat.com
Cc: gleb@kernel.org, mtosatti@redhat.com, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 08/11] KVM: MMU: use page track for non-leaf shadow pages
Date: Tue, 15 Dec 2015 15:59:24 +0800	[thread overview]
Message-ID: <566FC85C.9050502@linux.intel.com> (raw)
In-Reply-To: <566FC6B8.9010008@linux.intel.com>


On 12/15/2015 03:52 PM, Kai Huang wrote:
>
>
> On 12/01/2015 02:26 AM, Xiao Guangrong wrote:
>> non-leaf shadow pages are always write protected, it can be the user
>> of page track
>>
>> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
>> ---
>>   arch/x86/include/asm/kvm_page_track.h |  8 +++++
>>   arch/x86/kvm/mmu.c                    | 26 +++++++++++++---
>>   arch/x86/kvm/page_track.c             | 58 
>> +++++++++++++++++++++++------------
>>   3 files changed, 67 insertions(+), 25 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/kvm_page_track.h 
>> b/arch/x86/include/asm/kvm_page_track.h
>> index 6744234..3447dac 100644
>> --- a/arch/x86/include/asm/kvm_page_track.h
>> +++ b/arch/x86/include/asm/kvm_page_track.h
>> @@ -41,8 +41,16 @@ int kvm_page_track_create_memslot(struct 
>> kvm_memory_slot *slot,
>>   void kvm_page_track_free_memslot(struct kvm_memory_slot *free,
>>                    struct kvm_memory_slot *dont);
>>   +void
>> +kvm_slot_page_track_add_page_nolock(struct kvm *kvm,
>> +                    struct kvm_memory_slot *slot, gfn_t gfn,
>> +                    enum kvm_page_track_mode mode);
>>   void kvm_page_track_add_page(struct kvm *kvm, gfn_t gfn,
>>                    enum kvm_page_track_mode mode);
>> +void kvm_slot_page_track_remove_page_nolock(struct kvm *kvm,
>> +                        struct kvm_memory_slot *slot,
>> +                        gfn_t gfn,
>> +                        enum kvm_page_track_mode mode);
>>   void kvm_page_track_remove_page(struct kvm *kvm, gfn_t gfn,
>>                   enum kvm_page_track_mode mode);
>>   bool kvm_page_track_check_mode(struct kvm_vcpu *vcpu, gfn_t gfn,
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index b23f9fc..5a2ca73 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -806,11 +806,17 @@ static void account_shadowed(struct kvm *kvm, 
>> struct kvm_mmu_page *sp)
>>       struct kvm_memory_slot *slot;
>>       gfn_t gfn;
>>   +    kvm->arch.indirect_shadow_pages++;
>>       gfn = sp->gfn;
>>       slots = kvm_memslots_for_spte_role(kvm, sp->role);
>>       slot = __gfn_to_memslot(slots, gfn);
>> +
>> +    /* the non-leaf shadow pages are keeping readonly. */
>> +    if (sp->role.level > PT_PAGE_TABLE_LEVEL)
>> +        return kvm_slot_page_track_add_page_nolock(kvm, slot, gfn,
>> +                            KVM_PAGE_TRACK_WRITE);
>> +
>>       kvm_mmu_gfn_disallow_lpage(slot, gfn);
>> -    kvm->arch.indirect_shadow_pages++;
>>   }
>>     static void unaccount_shadowed(struct kvm *kvm, struct 
>> kvm_mmu_page *sp)
>> @@ -819,11 +825,15 @@ static void unaccount_shadowed(struct kvm *kvm, 
>> struct kvm_mmu_page *sp)
>>       struct kvm_memory_slot *slot;
>>       gfn_t gfn;
>>   +    kvm->arch.indirect_shadow_pages--;
>>       gfn = sp->gfn;
>>       slots = kvm_memslots_for_spte_role(kvm, sp->role);
>>       slot = __gfn_to_memslot(slots, gfn);
>> +    if (sp->role.level > PT_PAGE_TABLE_LEVEL)
>> +        return kvm_slot_page_track_remove_page_nolock(kvm, slot, gfn,
>> +                            KVM_PAGE_TRACK_WRITE);
>> +
>>       kvm_mmu_gfn_allow_lpage(slot, gfn);
>> -    kvm->arch.indirect_shadow_pages--;
>>   }
>>     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?
>
>>           if (level > PT_PAGE_TABLE_LEVEL && need_sync)
>>               kvm_sync_pages(vcpu, gfn);
>> -
>> -        account_shadowed(vcpu->kvm, sp);
>>       }
>>       sp->mmu_valid_gen = vcpu->kvm->arch.mmu_valid_gen;
>>       init_shadow_page_table(sp);
>> diff --git a/arch/x86/kvm/page_track.c b/arch/x86/kvm/page_track.c
>> index 84420df..87554d3 100644
>> --- a/arch/x86/kvm/page_track.c
>> +++ b/arch/x86/kvm/page_track.c
>> @@ -77,6 +77,26 @@ static void update_gfn_track(struct 
>> kvm_memory_slot *slot, gfn_t gfn,
>>       WARN_ON(val < 0);
>>   }
>>   +void
>> +kvm_slot_page_track_add_page_nolock(struct kvm *kvm,
>> +                    struct kvm_memory_slot *slot, gfn_t gfn,
>> +                    enum kvm_page_track_mode mode)
>> +{
>> +    WARN_ON(!check_mode(mode));
>> +
>> +    update_gfn_track(slot, gfn, mode, 1);
>> +
>> +    /*
>> +     * new track stops large page mapping for the
>> +     * tracked page.
>> +     */
>> +    kvm_mmu_gfn_disallow_lpage(slot, gfn);
>> +
>> +    if (mode == KVM_PAGE_TRACK_WRITE)
>> +        if (kvm_mmu_slot_gfn_write_protect(kvm, slot, gfn))
>> +            kvm_flush_remote_tlbs(kvm);
>> +}
>> +
>>   /*
>>    * add guest page to the tracking pool so that corresponding access 
>> on that
>>    * page will be intercepted.
>> @@ -101,21 +121,27 @@ void kvm_page_track_add_page(struct kvm *kvm, 
>> gfn_t gfn,
>>           slot = __gfn_to_memslot(slots, gfn);
>>             spin_lock(&kvm->mmu_lock);
>> -        update_gfn_track(slot, gfn, mode, 1);
>> -
>> -        /*
>> -         * new track stops large page mapping for the
>> -         * tracked page.
>> -         */
>> -        kvm_mmu_gfn_disallow_lpage(slot, gfn);
>> -
>> -        if (mode == KVM_PAGE_TRACK_WRITE)
>> -            if (kvm_mmu_slot_gfn_write_protect(kvm, slot, gfn))
>> -                kvm_flush_remote_tlbs(kvm);
>> +        kvm_slot_page_track_add_page_nolock(kvm, slot, gfn, mode);
>>           spin_unlock(&kvm->mmu_lock);
>>       }
>>   }
>>   +void kvm_slot_page_track_remove_page_nolock(struct kvm *kvm,
>> +                        struct kvm_memory_slot *slot,
>> +                        gfn_t gfn,
>> +                        enum kvm_page_track_mode mode)
>> +{
>> +    WARN_ON(!check_mode(mode));
>> +
>> +    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);
>> +}
>> +
>>   /*
>>    * 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.
Should be patch 5. sorry again.

Thanks,
-Kai
>
> Thanks,
> -Kai
>> spin_unlock(&kvm->mmu_lock);
>>       }
>>   }
>
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