Paolo Bonzini <pbonzini@xxxxxxxxxx> writes:
> This will make it easier to support multiple address spaces in
> kvm_gfn_to_hva_cache_init. Instead of having to check the address
> space id, we can keep on checking just the generation number.
>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> virt/kvm/kvm_main.c | 24 ++++++++++++++++--------
> 1 file changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index e21bac7ed5d3..a83c186cefc1 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -506,11 +506,6 @@ static struct kvm_memslots *kvm_alloc_memslots(void)
> if (!slots)
> return NULL;
>
> - /*
> - * Init kvm generation close to the maximum to easily test the
> - * code of handling generation number wrap-around.
> - */
> - slots->generation = -150;
> for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
> slots->id_to_index[i] = slots->memslots[i].id = i;
>
> @@ -641,9 +636,16 @@ static struct kvm *kvm_create_vm(unsigned long type)
>
> r = -ENOMEM;
> for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> - kvm->memslots[i] = kvm_alloc_memslots();
> - if (!kvm->memslots[i])
> + struct kvm_memslots *slots = kvm_alloc_memslots();
> + if (!slots)
> goto out_err_no_srcu;
> + /*
> + * Generations must be different for each address space.
> + * Init kvm generation close to the maximum to easily test the
> + * code of handling generation number wrap-around.
> + */
> + slots->generation = i * 2 - 150;
> + rcu_assign_pointer(kvm->memslots[i], slots);
> }
I can't seem to understand why rcu_assign_pointer wasn't used before.
kvm->memslots[i] was a rcu protected pointer even before this change,
right ?
> if (init_srcu_struct(&kvm->srcu))
> @@ -870,8 +872,14 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
> * Increment the new memslot generation a second time. This prevents
> * vm exits that race with memslot updates from caching a memslot
> * generation that will (potentially) be valid forever.
> + *
> + * Generations must be unique even across address spaces. We do not need
> + * a global counter for that, instead the generation space is evenly split
> + * across address spaces. For example, with two address spaces, address
> + * space 0 will use generations 0, 4, 8, ... while * address space 1 will
> + * use generations 2, 6, 10, 14, ...
> */
> - slots->generation++;
> + slots->generation += KVM_ADDRESS_SPACE_NUM * 2 - 1;
>
> kvm_arch_memslots_updated(kvm, slots);
