Re: [PATCH v3.1 02/37] KVM: s390/interrupt: do not pin adapter interrupt pages

David Hildenbrand
2020-02-21T09:50:38Z

On 21.02.20 09:09, Christian Borntraeger wrote:
> From: Ulrich Weigand <Ulrich.Weigand@de.ibm.com>
>
> The adapter interrupt page containing the indicator bits is currently
> pinned. That means that a guest with many devices can pin a lot of
> memory pages in the host. This also complicates the reference tracking
> which is needed for memory management handling of protected virtual
> machines. It might also have some strange side effects for madvise
> MADV_DONTNEED and other things.
>
> We can simply try to get the userspace page set the bits and free the
> page. By storing the userspace address in the irq routing entry instead
> of the guest address we can actually avoid many lookups and list walks
> so that this variant is very likely not slower.
>
> If userspace messes around with the memory slots the worst thing that
> can happen is that we write to some other memory within that process.
> As we get the the page with FOLL_WRITE this can also not be used to
> write to shared read-only pages.
>
> Signed-off-by: Ulrich Weigand <Ulrich.Weigand@de.ibm.com>
> [borntraeger@de.ibm.com: patch simplification]
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> ---
> Documentation/virt/kvm/devices/s390_flic.rst | 11 +-
> arch/s390/include/asm/kvm_host.h | 3 -
> arch/s390/kvm/interrupt.c | 172 ++++++-------------
> 3 files changed, 52 insertions(+), 134 deletions(-)
>
> diff --git a/Documentation/virt/kvm/devices/s390_flic.rst b/Documentation/virt/kvm/devices/s390_flic.rst
> index 954190da7d04..ea96559ba501 100644
> --- a/Documentation/virt/kvm/devices/s390_flic.rst
> +++ b/Documentation/virt/kvm/devices/s390_flic.rst
> @@ -108,16 +108,9 @@ Groups:
> mask or unmask the adapter, as specified in mask
>
> KVM_S390_IO_ADAPTER_MAP
> - perform a gmap translation for the guest address provided in addr,
> - pin a userspace page for the translated address and add it to the
> - list of mappings
> -
> - .. note:: A new mapping will be created unconditionally; therefore,
> - the calling code should avoid making duplicate mappings.
> -
> + This is now a no-op. The mapping is purely done by the irq route.
> KVM_S390_IO_ADAPTER_UNMAP
> - release a userspace page for the translated address specified in addr
> - from the list of mappings
> + This is now a no-op. The mapping is purely done by the irq route.
>
> KVM_DEV_FLIC_AISM
> modify the adapter-interruption-suppression mode for a given isc if the
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 1726224e7772..d058289385a5 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -701,9 +701,6 @@ struct s390_io_adapter {
> bool masked;
> bool swap;
> bool suppressible;
> - struct rw_semaphore maps_lock;
> - struct list_head maps;
> - atomic_t nr_maps;
> };
>
> #define MAX_S390_IO_ADAPTERS ((MAX_ISC + 1) * 8)
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index c06c89d370a7..50ccadaf4953 100644
> --- a/arch/s390/kvm/interrupt.c
> +++ b/arch/s390/kvm/interrupt.c
> @@ -2,7 +2,7 @@
> /*
> * handling kvm guest interrupts
> *
> - * Copyright IBM Corp. 2008, 2015
> + * Copyright IBM Corp. 2008, 2020
> *
> * Author(s): Carsten Otte <cotte@de.ibm.com>
> */
> @@ -2327,9 +2327,6 @@ static int register_io_adapter(struct kvm_device *dev,
> if (!adapter)
> return -ENOMEM;
>
> - INIT_LIST_HEAD(&adapter->maps);
> - init_rwsem(&adapter->maps_lock);
> - atomic_set(&adapter->nr_maps, 0);
> adapter->id = adapter_info.id;
> adapter->isc = adapter_info.isc;
> adapter->maskable = adapter_info.maskable;
> @@ -2354,87 +2351,12 @@ int kvm_s390_mask_adapter(struct kvm *kvm, unsigned int id, bool masked)
> return ret;
> }
>
> -static int kvm_s390_adapter_map(struct kvm *kvm, unsigned int id, __u64 addr)
> -{
> - struct s390_io_adapter *adapter = get_io_adapter(kvm, id);
> - struct s390_map_info *map;
> - int ret;
> -
> - if (!adapter || !addr)
> - return -EINVAL;
> -
> - map = kzalloc(sizeof(*map), GFP_KERNEL);
> - if (!map) {
> - ret = -ENOMEM;
> - goto out;
> - }
> - INIT_LIST_HEAD(&map->list);
> - map->guest_addr = addr;
> - map->addr = gmap_translate(kvm->arch.gmap, addr);
> - if (map->addr == -EFAULT) {
> - ret = -EFAULT;
> - goto out;
> - }
> - ret = get_user_pages_fast(map->addr, 1, FOLL_WRITE, &map->page);
> - if (ret < 0)
> - goto out;
> - BUG_ON(ret != 1);
> - down_write(&adapter->maps_lock);
> - if (atomic_inc_return(&adapter->nr_maps) < MAX_S390_ADAPTER_MAPS) {
> - list_add_tail(&map->list, &adapter->maps);
> - ret = 0;
> - } else {
> - put_page(map->page);
> - ret = -EINVAL;
> - }
> - up_write(&adapter->maps_lock);
> -out:
> - if (ret)
> - kfree(map);
> - return ret;
> -}
> -
> -static int kvm_s390_adapter_unmap(struct kvm *kvm, unsigned int id, __u64 addr)
> -{
> - struct s390_io_adapter *adapter = get_io_adapter(kvm, id);
> - struct s390_map_info *map, *tmp;
> - int found = 0;
> -
> - if (!adapter || !addr)
> - return -EINVAL;
> -
> - down_write(&adapter->maps_lock);
> - list_for_each_entry_safe(map, tmp, &adapter->maps, list) {
> - if (map->guest_addr == addr) {
> - found = 1;
> - atomic_dec(&adapter->nr_maps);
> - list_del(&map->list);
> - put_page(map->page);
> - kfree(map);
> - break;
> - }
> - }
> - up_write(&adapter->maps_lock);
> -
> - return found ? 0 : -EINVAL;
> -}
> -
> void kvm_s390_destroy_adapters(struct kvm *kvm)
> {
> int i;
> - struct s390_map_info *map, *tmp;
>
> - for (i = 0; i < MAX_S390_IO_ADAPTERS; i++) {
> - if (!kvm->arch.adapters[i])
> - continue;
> - list_for_each_entry_safe(map, tmp,
> - &kvm->arch.adapters[i]->maps, list) {
> - list_del(&map->list);
> - put_page(map->page);
> - kfree(map);
> - }
> + for (i = 0; i < MAX_S390_IO_ADAPTERS; i++)
> kfree(kvm->arch.adapters[i]);
> - }
> }
>
> static int modify_io_adapter(struct kvm_device *dev,
> @@ -2456,12 +2378,13 @@ static int modify_io_adapter(struct kvm_device *dev,
> if (ret > 0)
> ret = 0;
> break;
> + /*
> + * We resolve the gpa to hva when setting the IRQ routing. the set_irq
> + * code uses get_user_pages_remote() to do the actual write.
> + */
> case KVM_S390_IO_ADAPTER_MAP:
> - ret = kvm_s390_adapter_map(dev->kvm, req.id, req.addr);
> - break;
> case KVM_S390_IO_ADAPTER_UNMAP:
> - ret = kvm_s390_adapter_unmap(dev->kvm, req.id, req.addr);
> - break;
> + return 0;
> default:
> ret = -EINVAL;
> }
> @@ -2699,19 +2622,17 @@ static unsigned long get_ind_bit(__u64 addr, unsigned long bit_nr, bool swap)
> return swap ? (bit ^ (BITS_PER_LONG - 1)) : bit;
> }
>
> -static struct s390_map_info *get_map_info(struct s390_io_adapter *adapter,
> - u64 addr)
> +static struct page *get_map_page(struct kvm *kvm,
> + struct s390_io_adapter *adapter,
> + u64 uaddr)
> {
> - struct s390_map_info *map;
> -
> - if (!adapter)
> - return NULL;
> + struct page *page = NULL;
>
> - list_for_each_entry(map, &adapter->maps, list) {
> - if (map->guest_addr == addr)
> - return map;
> - }
> - return NULL;
> + down_read(&kvm->mm->mmap_sem);
> + get_user_pages_remote(NULL, kvm->mm, uaddr, 1, FOLL_WRITE,
> + &page, NULL, NULL);
> + up_read(&kvm->mm->mmap_sem);
> + return page;
> }
>
> static int adapter_indicators_set(struct kvm *kvm,
> @@ -2720,30 +2641,35 @@ static int adapter_indicators_set(struct kvm *kvm,
> {
> unsigned long bit;
> int summary_set, idx;
> - struct s390_map_info *info;
> + struct page *ind_page, *summary_page;
> void *map;
>
> - info = get_map_info(adapter, adapter_int->ind_addr);
> - if (!info)
> + ind_page = get_map_page(kvm, adapter, adapter_int->ind_addr);
> + if (!ind_page)
> return -1;
> - map = page_address(info->page);
> - bit = get_ind_bit(info->addr, adapter_int->ind_offset, adapter->swap);
> - set_bit(bit, map);
> - idx = srcu_read_lock(&kvm->srcu);
> - mark_page_dirty(kvm, info->guest_addr >> PAGE_SHIFT);
> - set_page_dirty_lock(info->page);
> - info = get_map_info(adapter, adapter_int->summary_addr);
> - if (!info) {
> - srcu_read_unlock(&kvm->srcu, idx);
> + summary_page = get_map_page(kvm, adapter, adapter_int->summary_addr);
> + if (!summary_page) {
> + put_page(ind_page);
> return -1;
> }
> - map = page_address(info->page);
> - bit = get_ind_bit(info->addr, adapter_int->summary_offset,
> - adapter->swap);
> +
> + idx = srcu_read_lock(&kvm->srcu);
> + map = page_address(ind_page);
> + bit = get_ind_bit(adapter_int->ind_addr,
> + adapter_int->ind_offset, adapter->swap);
> + set_bit(bit, map);
> + mark_page_dirty(kvm, adapter_int->ind_addr >> PAGE_SHIFT);
> + set_page_dirty_lock(ind_page);
> + map = page_address(summary_page);
> + bit = get_ind_bit(adapter_int->summary_addr,
> + adapter_int->summary_offset, adapter->swap);
> summary_set = test_and_set_bit(bit, map);
> - mark_page_dirty(kvm, info->guest_addr >> PAGE_SHIFT);
> - set_page_dirty_lock(info->page);
> + mark_page_dirty(kvm, adapter_int->summary_addr >> PAGE_SHIFT);
> + set_page_dirty_lock(summary_page);
> srcu_read_unlock(&kvm->srcu, idx);
> +
> + put_page(ind_page);
> + put_page(summary_page);
> return summary_set ? 0 : 1;
> }
>
> @@ -2765,9 +2691,7 @@ static int set_adapter_int(struct kvm_kernel_irq_routing_entry *e,
> adapter = get_io_adapter(kvm, e->adapter.adapter_id);
> if (!adapter)
> return -1;
> - down_read(&adapter->maps_lock);
> ret = adapter_indicators_set(kvm, adapter, &e->adapter);
> - up_read(&adapter->maps_lock);
> if ((ret > 0) && !adapter->masked) {
> ret = kvm_s390_inject_airq(kvm, adapter);
> if (ret == 0)
> @@ -2818,23 +2742,27 @@ int kvm_set_routing_entry(struct kvm *kvm,
> struct kvm_kernel_irq_routing_entry *e,
> const struct kvm_irq_routing_entry *ue)
> {
> - int ret;
> + u64 uaddr;
>
> switch (ue->type) {
> + /* we store the userspace addresses instead of the guest addresses */
> case KVM_IRQ_ROUTING_S390_ADAPTER:
> e->set = set_adapter_int;
> - e->adapter.summary_addr = ue->u.adapter.summary_addr;
> - e->adapter.ind_addr = ue->u.adapter.ind_addr;
> + uaddr = gmap_translate(kvm->arch.gmap, ue->u.adapter.summary_addr);
> + if (uaddr == -EFAULT)
> + return -EFAULT;
> + e->adapter.summary_addr = uaddr;
> + uaddr = gmap_translate(kvm->arch.gmap, ue->u.adapter.ind_addr);
> + if (uaddr == -EFAULT)
> + return -EFAULT;
> + e->adapter.ind_addr = uaddr;
> e->adapter.summary_offset = ue->u.adapter.summary_offset;
> e->adapter.ind_offset = ue->u.adapter.ind_offset;
> e->adapter.adapter_id = ue->u.adapter.adapter_id;
> - ret = 0;
> - break;
> + return 0;
> default:
> - ret = -EINVAL;
> + return -EINVAL;
> }
> -
> - return ret;
> }
>
> int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e, struct kvm *kvm,
>

Acked-by: David Hildenbrand <david@redhat.com>

--
Thanks,

David / dhildenb