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SubjectRe: [PATCH v6 2/7] KVM: MMU: delete shadow page from hash list in kvm_mmu_prepare_zap_page
On Fri, May 17, 2013 at 05:12:57AM +0800, Xiao Guangrong wrote:
> Move deletion shadow page from the hash list from kvm_mmu_commit_zap_page to
> kvm_mmu_prepare_zap_page so that we can call kvm_mmu_commit_zap_page
> once for multiple kvm_mmu_prepare_zap_page that can help us to avoid
> unnecessary TLB flush
>
Don't we call kvm_mmu_commit_zap_page() once for multiple
kvm_mmu_prepare_zap_page() now when possible? kvm_mmu_commit_zap_page()
gets a list as a parameter. I am not against the change, but wish to
understand it better.

> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
> ---
> arch/x86/kvm/mmu.c | 8 ++++++--
> 1 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 40d7b2d..682ecb4 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -1466,7 +1466,7 @@ static inline void kvm_mod_used_mmu_pages(struct kvm *kvm, int nr)
> static void kvm_mmu_free_page(struct kvm_mmu_page *sp)
> {
> ASSERT(is_empty_shadow_page(sp->spt));
> - hlist_del(&sp->hash_link);
> +
> list_del(&sp->link);
> free_page((unsigned long)sp->spt);
> if (!sp->role.direct)
> @@ -1655,7 +1655,8 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
>
> #define for_each_gfn_indirect_valid_sp(_kvm, _sp, _gfn) \
> for_each_gfn_sp(_kvm, _sp, _gfn) \
> - if ((_sp)->role.direct || (_sp)->role.invalid) {} else
> + if ((_sp)->role.direct || \
> + ((_sp)->role.invalid && WARN_ON(1))) {} else
>
> /* @sp->gfn should be write-protected at the call site */
> static int __kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
> @@ -2074,6 +2075,9 @@ static int kvm_mmu_prepare_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp,
> unaccount_shadowed(kvm, sp->gfn);
> if (sp->unsync)
> kvm_unlink_unsync_page(kvm, sp);
> +
> + hlist_del_init(&sp->hash_link);
> +
What about moving this inside if() bellow and making it hlist_del()?
Leave the page on the hash if root_count is non zero.

> if (!sp->root_count) {
> /* Count self */
> ret++;
> --
> 1.7.7.6

--
Gleb.


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