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DateMon, 31 May 2010 14:14:35 +0300
FromAvi Kivity <>
SubjectRe: [PATCH 1/5] KVM: MMU: introduce some macros to cleanup hlist traverseing
On 05/31/2010 05:00 AM, Xiao Guangrong wrote:
>
>>
>>> +
>>> +#define for_each_gfn_indirect_sp(kvm, sp, gfn, pos, n) \
>>> + hlist_for_each_entry_safe(sp, pos, n, \
>>> +&kvm->arch.mmu_page_hash[kvm_page_table_hashfn(gfn)], hash_link)\
>>> + if (sp->gfn == gfn&& !sp->role.direct)
>>> +
>>> +#define for_each_gfn_indirect_valid_sp(kvm, sp, gfn, pos, n) \
>>> + hlist_for_each_entry_safe(sp, pos, n, \
>>> +&kvm->arch.mmu_page_hash[kvm_page_table_hashfn(gfn)], hash_link)\
>>> + if (sp->gfn == gfn&& !sp->role.direct&& \
>>> + !sp->role.invalid)
>>>
>>>
>> Shouldn't we always skip invalid gfns?
>>
> Actually, in kvm_mmu_unprotect_page() function, it need find out
> invalid shadow pages:
>
> | hlist_for_each_entry_safe(sp, node, n, bucket, hash_link)
> | if (sp->gfn == gfn&& !sp->role.direct) {
> | pgprintk("%s: gfn %lx role %x\n", __func__, gfn,
> | sp->role.word);
> | r = 1;
> | if (kvm_mmu_zap_page(kvm, sp))
> | goto restart;
> | }
>
> I'm not sure whether we can skip invalid sp here, since it can change this
> function's return value. :-(
>

Hm. Invalid pages don't need to be write protected. So I think you can
patch unprotect_page() to ignore invalid pages, and then you can convert
it to the new macros which ignore invalid pages as well.

The invariant is: if an sp exists with !role.invalid and !unsync, then
the page must be write protected.


>> What about providing both gfn and role to the macro?
>>
>>
> In current code, no code simply use role and gfn to find sp,
> in kvm_mmu_get_page(), we need do other work for
> 'sp->gfn == gfn&& sp->role != role' sp, and other functions only need compare
> some members in role, but not all members.
>

How about just gfn? I think everything compares against that!

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.



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