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

Christoffer Dall
2017-10-30T06:03:58Z

On Mon, Oct 30, 2017 at 03:19:54AM +0000, Marc Zyngier wrote:
> 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 + * If the table is no longer valid, we clear the associated cached data.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.
>

Yes, no problem.

> > + 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>
>

Also,

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>