On Tue, Feb 05, 2013 at 04:55:37PM +0800, Xiao Guangrong wrote:
> If a shadow page is being zapped or a host page is going to be freed, kvm
> will drop all the reverse-mappings on the shadow page or the gfn. Currently,
> it drops the reverse-mapping one by one - it deletes the first reverse mapping,
> then moves other reverse-mapping between the description-table. When the
> last description-table become empty, it will be freed.
>
> It works well if we only have a few reverse-mappings, but some pte_lists are
> very long, during my tracking, i saw some gfns have more than 200 sptes listed
> on its pte-list (1G memory in guest on softmmu). Optimization for dropping such
> long pte-list is worthwhile, at lease it is good for deletion memslots and
> ksm/thp merge pages.
>
> This patch introduce a better way to optimize for this case, it walks all the
> reverse-mappings and clear them, then free all description-tables together.
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/kvm/mmu.c | 36 +++++++++++++++++++++++++++---------
> 1 files changed, 27 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 58f813a..aa7a887 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -945,6 +945,25 @@ static void pte_list_remove(u64 *spte, unsigned long *pte_list)
> }
> }
>
> +static void pte_list_destroy(unsigned long *pte_list)
> +{
> + struct pte_list_desc *desc;
> + unsigned long list_value = *pte_list;
> +
> + *pte_list = 0;
> +
> + if (!(list_value & 1))
> + return;
> +
> + desc = (struct pte_list_desc *)(list_value & ~1ul);
> + while (desc) {
> + struct pte_list_desc *next_desc = desc->more;
> +
> + mmu_free_pte_list_desc(desc);
> + desc = next_desc;
> + }
> +}
> +
> /*
> * Used by the following functions to iterate through the sptes linked by a
> * pte_list. All fields are private and not assumed to be used outside.
> @@ -1183,17 +1202,17 @@ static bool rmap_write_protect(struct kvm *kvm, u64 gfn)
> static int kvm_unmap_rmapp(struct kvm *kvm, unsigned long *rmapp,
> struct kvm_memory_slot *slot, unsigned long data)
> {
> - u64 *sptep;
> struct pte_list_iterator iter;
> + u64 *sptep;
> int need_tlb_flush = 0;
>
> -restart:
> for_each_spte_in_rmap(*rmapp, iter, sptep) {
> - drop_spte(kvm, sptep);
> + mmu_spte_clear_track_bits(sptep);
> need_tlb_flush = 1;
> - goto restart;
> }
>
> + pte_list_destroy(rmapp);
> +
> return need_tlb_flush;
> }
>
> @@ -2016,11 +2035,10 @@ static void kvm_mmu_unlink_parents(struct kvm *kvm, struct kvm_mmu_page *sp)
> u64 *sptep;
> struct pte_list_iterator iter;
>
> -restart:
> - for_each_spte_in_pte_list(sp->parent_ptes, iter, sptep) {
> - drop_parent_pte(sp, sptep);
> - goto restart;
> - }
> + for_each_spte_in_pte_list(sp->parent_ptes, iter, sptep)
> + mmu_spte_clear_no_track(sptep);
> +
> + pte_list_destroy(&sp->parent_ptes);
> }
Do we lose the crash information of pte_list_remove?
It has been shown to be useful in several cases.
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