On Thu, Sep 05, 2013 at 06:29:12PM +0800, Xiao Guangrong wrote:
> The basic idea is from nulls list which uses a nulls to indicate
> whether the desc is moved to different pte-list
>
> Note, we should do bottom-up walk in the desc since we always move
> the bottom entry to the deleted position. A desc only has 3 entries
> in the current code so it is not a problem now, but the issue will
> be triggered if we expend the size of desc in the further development
>
> Thanks to SLAB_DESTROY_BY_RCU, the desc can be quickly reused
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/kvm/mmu.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 53 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index c5f1b27..3e1432f 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -975,6 +975,10 @@ static int count_spte_number(struct pte_list_desc *desc)
> return first_free + desc_num * PTE_LIST_EXT;
> }
>
> +#define rcu_assign_pte_list(pte_list_p, value) \
> + rcu_assign_pointer(*(unsigned long __rcu **)(pte_list_p), \
> + (unsigned long *)(value))
> +
> /*
> * Pte mapping structures:
> *
> @@ -994,7 +998,7 @@ static int pte_list_add(struct kvm_vcpu *vcpu, u64 *spte,
>
> if (!*pte_list) {
> rmap_printk("pte_list_add: %p %llx 0->1\n", spte, *spte);
> - *pte_list = (unsigned long)spte;
> + rcu_assign_pte_list(pte_list, spte);
> return 0;
> }
>
> @@ -1004,7 +1008,7 @@ static int pte_list_add(struct kvm_vcpu *vcpu, u64 *spte,
> desc->sptes[0] = (u64 *)*pte_list;
> desc->sptes[1] = spte;
> desc_mark_nulls(pte_list, desc);
> - *pte_list = (unsigned long)desc | 1;
> + rcu_assign_pte_list(pte_list, (unsigned long)desc | 1);
> return 1;
> }
>
> @@ -1017,7 +1021,7 @@ static int pte_list_add(struct kvm_vcpu *vcpu, u64 *spte,
> new_desc = mmu_alloc_pte_list_desc(vcpu);
> new_desc->more = desc;
> desc = new_desc;
> - *pte_list = (unsigned long)desc | 1;
> + rcu_assign_pte_list(pte_list, (unsigned long)desc | 1);
> }
>
> free_pos = find_first_free(desc);
> @@ -1125,6 +1129,51 @@ static void pte_list_walk(unsigned long *pte_list, pte_list_walk_fn fn)
> WARN_ON(desc_get_nulls_value(desc) != pte_list);
> }
>
> +/* The caller should hold rcu lock. */
> +static void pte_list_walk_lockless(unsigned long *pte_list,
> + pte_list_walk_fn fn)
> +{
> + struct pte_list_desc *desc;
> + unsigned long pte_list_value;
> + int i;
> +
> +restart:
> + /*
> + * Force the pte_list to be reloaded.
> + *
> + * See the comments in hlist_nulls_for_each_entry_rcu().
> + */
> + barrier();
> + pte_list_value = *rcu_dereference(pte_list);
> + if (!pte_list_value)
> + return;
> +
> + if (!(pte_list_value & 1))
> + return fn((u64 *)pte_list_value);
> +
> + desc = (struct pte_list_desc *)(pte_list_value & ~1ul);
> + while (!desc_is_a_nulls(desc)) {
> + /*
> + * We should do top-down walk since we always use the higher
> + * indices to replace the deleted entry if only one desc is
> + * used in the rmap when a spte is removed. Otherwise the
> + * moved entry will be missed.
> + */
> + for (i = PTE_LIST_EXT - 1; i >= 0; i--)
> + if (desc->sptes[i])
> + fn(desc->sptes[i]);
> +
> + desc = rcu_dereference(desc->more);
> +
> + /* It is being initialized. */
> + if (unlikely(!desc))
> + goto restart;
> + }
> +
> + if (unlikely(desc_get_nulls_value(desc) != pte_list))
> + goto restart;
> +}
> +
> static unsigned long *__gfn_to_rmap(gfn_t gfn, int level,
> struct kvm_memory_slot *slot)
> {
> @@ -4651,7 +4700,7 @@ int kvm_mmu_module_init(void)
> {
> pte_list_desc_cache = kmem_cache_create("pte_list_desc",
> sizeof(struct pte_list_desc),
> - 0, 0, NULL);
> + 0, SLAB_DESTROY_BY_RCU, NULL);
Haven't we agreed that constructor is needed for the cache?
> if (!pte_list_desc_cache)
> goto nomem;
>
> --
> 1.8.1.4
--
Gleb.
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