linux-kernel - Re: [PATCH 07/10] KVM: x86: MMU: Encapsulate the type of rmap-chain head in a new struct

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Date:	Thu, 19 Nov 2015 11:23:58 +0900
From:	Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	mtosatti@...hat.com
Subject: Re: [PATCH 07/10] KVM: x86: MMU: Encapsulate the type of rmap-chain
 head in a new struct

On 2015/11/18 18:09, Paolo Bonzini wrote:

> On 18/11/2015 04:21, Xiao Guangrong wrote:

>> On 11/12/2015 07:55 PM, Takuya Yoshikawa wrote:
>>> @@ -1720,7 +1724,7 @@ static struct kvm_mmu_page
>>> *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu,
>>>         * this feature. See the comments in kvm_zap_obsolete_pages().
>>>         */
>>>        list_add(&sp->link, &vcpu->kvm->arch.active_mmu_pages);
>>> -    sp->parent_ptes = 0;
>>> +    sp->parent_ptes.val = 0;
>>
>> The sp is allocated from kmem_cache_zalloc() so explicitly initialize it
>> to zero is not needed.
>
> Right, but it should be a separate patch.
>
> Takuya, since you are going to send another version of this series, can
> you also:

Yes, I'm preparing to do so.

> 1) move this patch either to the beginning or to the end
>
> 2) include "KVM: x86: always set accessed bit in shadow PTEs", also near
> the beginning of the series?

Commit 1c9a5e19b1af8a2c ("KVM: x86: MMU: always set accessed bit
in shadow PTEs") will be the first.

Then, the ordering will become something like this:

02: Encapsulate the type of rmap-chain head in a new struct
03: Remove unused parameter of __direct_map()
04: Add helper function to clear a bit in unsync child bitmap
05: Make mmu_set_spte() return emulate value
06: Remove is_rmap_spte() and use is_shadow_present_pte()

These five seem to be easy ones for you to apply: since patch 02
touches many places, it should go first to become the base of the
following work.

07: Consolidate BUG_ON checks for reverse-mapped sptes

I will change the WARN_ON to BUG_ON.  // Marcelo's comment

08: Move initialization of parent_ptes out from kvm_mmu_alloc_page()

In this patch, I will delete "sp->parent_ptes.val = 0;" line since
this is the problem of kvm_mmu_alloc_page(), though not a new one.
   // Xiao's comment

09: Use for_each_rmap_spte macro instead of pte_list_walk()

There is some confusion between us: Paolo and I agreed that the
patch keeps the original way and calls mark_unsync() the same way
as before, but there are still comments from Marcelo and Xiao and
those comments seem to explain the code differently.

I will check again, but I may not change this one and the following
two patches in the next version.  If we can eliminate some of the
mark_unsync() calls, that will be kind of an optimization which this
series does not intend to achieve.

Anyway, by moving the non-trivial two patches (09 and 10) here,
reviewing will become easier and you can apply the other patches
separately.

10: Move parent_pte handling from kvm_mmu_get_page()
     to link_shadow_page()
11: Remove unused parameter parent_pte from kvm_mmu_get_page()

Thanks,
   Takuya

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