Re: [PATCH v6 7/9] KVM: arm/arm64: vgic-its: Free caches when GITS_BASER Valid bit is cleared

Marc Zyngier
2017-10-30T03:19:54Z

On Thu, Oct 26 2017 at 6:23:09 pm BST, Eric Auger <eric.auger@redhat.com> wrote:
> When the GITS_BASER<n>.Valid gets cleared, the data structures in
> guest RAM are not valid anymore. The device, collection
> and LPI lists stored in the in-kernel ITS represent the same
> information in some form of cache. So let's void the cache.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>
> ---
> v5 -> v6:
> - rename type into device_type and revert tthe u64 -> int change
> - remove the default clause
> - take the its mutex lock around vgic_its_free_device/collection_list
>
> v4 -> v5:
> - add comment about locking
>
> v2 -> v3:
> - add a comment and clear cache in if block
> ---
> virt/kvm/arm/vgic/vgic-its.c | 26 ++++++++++++++++++++++----
> 1 file changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 5b7be85..2a92d4d 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -1428,7 +1428,7 @@ static void vgic_mmio_write_its_baser(struct kvm *kvm,
> unsigned long val)
> {
> const struct vgic_its_abi *abi = vgic_its_get_abi(its);
> - u64 entry_size, device_type;
> + u64 entry_size, table_type;
> u64 reg, *regptr, clearbits = 0;
>
> /* When GITS_CTLR.Enable is 1, we ignore write accesses. */
> @@ -1439,12 +1439,12 @@ static void vgic_mmio_write_its_baser(struct kvm *kvm,
> case 0:
> regptr = &its->baser_device_table;
> entry_size = abi->dte_esz;
> - device_type = GITS_BASER_TYPE_DEVICE;
> + table_type = GITS_BASER_TYPE_DEVICE;
> break;
> case 1:
> regptr = &its->baser_coll_table;
> entry_size = abi->cte_esz;
> - device_type = GITS_BASER_TYPE_COLLECTION;
> + table_type = GITS_BASER_TYPE_COLLECTION;
> clearbits = GITS_BASER_INDIRECT;
> break;
> default:
> @@ -1456,10 +1456,28 @@ static void vgic_mmio_write_its_baser(struct kvm *kvm,
> reg &= ~clearbits;
>
> reg |= (entry_size - 1) << GITS_BASER_ENTRY_SIZE_SHIFT;
> - reg |= device_type << GITS_BASER_TYPE_SHIFT;
> + reg |= table_type << GITS_BASER_TYPE_SHIFT;
> reg = vgic_sanitise_its_baser(reg);
>
> *regptr = reg;
> +
> + /*
> + * If the table is no longer valid, we clear the associated cached data.
> + * Note: there cannot be any race with save/restore code which locks
> + * all vcpus.
> + */

nit: I found this comment to be pretty confusing, as it talks about
locks that we don't try to take here. The actual mutual exclusion is
done by taking the its_lock, which is also taken on the save/restore
path.

Christoffer: can you fix that when applying this patch? I don't think
there is a need for a respin of the series just for this.

> + if (!(reg & GITS_BASER_VALID)) {
> + mutex_lock(&its->its_lock);
> + switch (table_type) {
> + case GITS_BASER_TYPE_DEVICE:
> + vgic_its_free_device_list(kvm, its);
> + break;
> + case GITS_BASER_TYPE_COLLECTION:
> + vgic_its_free_collection_list(kvm, its);
> + break;
> + }
> + mutex_unlock(&its->its_lock);
> + }
> }
>
> static unsigned long vgic_mmio_read_its_ctlr(struct kvm *vcpu,

Otherwise:

Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>

Thanks,

M.
--
Jazz is not dead. It just smells funny.