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    Subject[PATCH 08/12] KVM: MMU: introduce nulls desc
    Date
    It likes nulls list and we use the pte-list as the nulls which can help us to
    detect whether the "desc" is moved to anther rmap then we can re-walk the rmap
    if that happened

    Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
    ---
    arch/x86/kvm/mmu.c | 35 ++++++++++++++++++++++++++++-------
    1 file changed, 28 insertions(+), 7 deletions(-)

    diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
    index 3013bb1..36caf6a 100644
    --- a/arch/x86/kvm/mmu.c
    +++ b/arch/x86/kvm/mmu.c
    @@ -918,6 +918,24 @@ static int mapping_level(struct kvm_vcpu *vcpu, gfn_t large_gfn)
    return level - 1;
    }

    +static void desc_mark_nulls(unsigned long *pte_list, struct pte_list_desc *desc)
    +{
    + unsigned long marker;
    +
    + marker = (unsigned long)pte_list | 1UL;
    + desc->more = (struct pte_list_desc *)marker;
    +}
    +
    +static bool desc_is_a_nulls(struct pte_list_desc *desc)
    +{
    + return (unsigned long)desc & 1;
    +}
    +
    +static unsigned long *desc_get_nulls_value(struct pte_list_desc *desc)
    +{
    + return (unsigned long *)((unsigned long)desc & ~1);
    +}
    +
    static int __find_first_free(struct pte_list_desc *desc)
    {
    int i;
    @@ -956,7 +974,7 @@ static int count_spte_number(struct pte_list_desc *desc)

    first_free = __find_first_free(desc);

    - for (desc_num = 0; desc->more; desc = desc->more)
    + for (desc_num = 0; !desc_is_a_nulls(desc->more); desc = desc->more)
    desc_num++;

    return first_free + desc_num * PTE_LIST_EXT;
    @@ -991,6 +1009,7 @@ static int pte_list_add(struct kvm_vcpu *vcpu, u64 *spte,
    desc = mmu_alloc_pte_list_desc(vcpu);
    desc->sptes[0] = (u64 *)*pte_list;
    desc->sptes[1] = spte;
    + desc_mark_nulls(pte_list, desc);
    *pte_list = (unsigned long)desc | 1;
    return 1;
    }
    @@ -1036,7 +1055,7 @@ pte_list_desc_remove_entry(unsigned long *pte_list,
    /*
    * Only one entry existing but still use a desc to store it?
    */
    - WARN_ON(!next_desc);
    + WARN_ON(desc_is_a_nulls(next_desc));

    mmu_free_pte_list_desc(first_desc);
    first_desc = next_desc;
    @@ -1050,7 +1069,7 @@ pte_list_desc_remove_entry(unsigned long *pte_list,
    * Only one entry in this desc, move the entry to the head
    * then the desc can be freed.
    */
    - if (!first_desc->sptes[1] && !first_desc->more) {
    + if (!first_desc->sptes[1] && desc_is_a_nulls(first_desc->more)) {
    *pte_list = (unsigned long)first_desc->sptes[0];
    mmu_free_pte_list_desc(first_desc);
    }
    @@ -1077,7 +1096,7 @@ static void pte_list_remove(u64 *spte, unsigned long *pte_list)

    rmap_printk("pte_list_remove: %p many->many\n", spte);
    desc = (struct pte_list_desc *)(*pte_list & ~1ul);
    - while (desc) {
    + while (!desc_is_a_nulls(desc)) {
    for (i = 0; i < PTE_LIST_EXT && desc->sptes[i]; ++i)
    if (desc->sptes[i] == spte) {
    pte_list_desc_remove_entry(pte_list,
    @@ -1103,11 +1122,13 @@ static void pte_list_walk(unsigned long *pte_list, pte_list_walk_fn fn)
    return fn((u64 *)*pte_list);

    desc = (struct pte_list_desc *)(*pte_list & ~1ul);
    - while (desc) {
    + while (!desc_is_a_nulls(desc)) {
    for (i = 0; i < PTE_LIST_EXT && desc->sptes[i]; ++i)
    fn(desc->sptes[i]);
    desc = desc->more;
    }
    +
    + WARN_ON(desc_get_nulls_value(desc) != pte_list);
    }

    static unsigned long *__gfn_to_rmap(gfn_t gfn, int level,
    @@ -1200,7 +1221,7 @@ static u64 *rmap_get_first(unsigned long rmap, struct rmap_iterator *iter)
    */
    static u64 *rmap_get_next(struct rmap_iterator *iter)
    {
    - if (iter->desc) {
    + if (iter->desc && !desc_is_a_nulls(iter->desc)) {
    if (iter->pos < PTE_LIST_EXT - 1) {
    u64 *sptep;

    @@ -1212,7 +1233,7 @@ static u64 *rmap_get_next(struct rmap_iterator *iter)

    iter->desc = iter->desc->more;

    - if (iter->desc) {
    + if (!desc_is_a_nulls(iter->desc)) {
    iter->pos = 0;
    /* desc->sptes[0] cannot be NULL */
    return iter->desc->sptes[iter->pos];
    --
    1.8.1.4


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