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SubjectRe: [PATCH 09/11] KVM: MMU: simplify mmu_need_write_protect
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On 12/15/2015 04:43 PM, Kai Huang wrote:
>
>
> On 12/01/2015 02:26 AM, Xiao Guangrong wrote:
>> Now, all non-leaf shadow page are page tracked, if gfn is not tracked
>> there is no non-leaf shadow page of gfn is existed, we can directly
>> make the shadow page of gfn to unsync
>>
>> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
>> ---
>> arch/x86/kvm/mmu.c | 26 ++++++++------------------
>> 1 file changed, 8 insertions(+), 18 deletions(-)
>>
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index 5a2ca73..f89e77f 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -2461,41 +2461,31 @@ static void __kvm_unsync_page(struct kvm_vcpu
>> *vcpu, struct kvm_mmu_page *sp)
>> kvm_mmu_mark_parents_unsync(sp);
>> }
>> -static void kvm_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn)
>> +static bool kvm_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn,
>> + bool can_unsync)
>> {
>> struct kvm_mmu_page *s;
>> for_each_gfn_indirect_valid_sp(vcpu->kvm, s, gfn) {
>> + if (!can_unsync)
>> + return true;
> How about moving this right before for_each_gfn_indirect_valid_sp? As
> can_unsync is passed as parameter, so there's no point checking it
> several times.
>
> A further thinking is can we move it to mmu_need_write_protect?
> Passing can_unsync as parameter to kvm_unsync_pages sounds a little
> bit odd.
>
>> +
>> if (s->unsync)
>> continue;
>> WARN_ON(s->role.level != PT_PAGE_TABLE_LEVEL);
> How about large page mapping? Such as if guest uses 2M mapping and its
> shadow is indirect, does above WARN_ON still meet? As you removed the
> PT level check in mmu_need_write_protect.
>
> Thanks,
> -Kai
Btw I also think this patch can be merged with patch 6.

Thanks,
-Kai
>> __kvm_unsync_page(vcpu, s);
>> }
>> +
>> + return false;
>> }
>
>> static bool mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
>> bool can_unsync)
>> {
>> - struct kvm_mmu_page *s;
>> - bool need_unsync = false;
>> -
>> if (kvm_page_track_check_mode(vcpu, gfn, KVM_PAGE_TRACK_WRITE))
>> return true;
>> - for_each_gfn_indirect_valid_sp(vcpu->kvm, s, gfn) {
>> - if (!can_unsync)
>> - return true;
>> -
>> - if (s->role.level != PT_PAGE_TABLE_LEVEL)
>> - return true;
>> -
>> - if (!s->unsync)
>> - need_unsync = true;
>> - }
>> - if (need_unsync)
>> - kvm_unsync_pages(vcpu, gfn);
>> -
>> - return false;
>> + return kvm_unsync_pages(vcpu, gfn, can_unsync);
>> }
>> static bool kvm_is_mmio_pfn(pfn_t pfn)
>
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