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

Cornelia Huck
2020-02-21T10:42:15Z

On Fri, 21 Feb 2020 03:09:42 -0500
Christian Borntraeger <borntraeger@de.ibm.com> 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(-)

(...)

> @@ -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.
> + */

What about:

"The following operations are no longer needed and therefore no-ops.
The gpa to hva translation is done when an IRQ route is set up. 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;

I think
ret = 0;
break;

would be better, as the other cases do not do a direct return, either.

> 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,

adapter seems to be unused in this function now? Should we remove it from the parameter list?

> + 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,