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SubjectRe: [PATCH 09/11] KVM: MMU: simplify mmu_need_write_protect
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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
> __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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