Re: [PATCH v2 05/10] KVM: arm/arm64: vgic-its: Check GITS_CBASER validity before processing commands

Andre Przywara
2017-10-06T14:38:29Z

Hi,

On 27/09/17 14:28, Eric Auger wrote:
> At the moment vgic_its_process_commands() does not
> check the CBASER is valid before processing any command.
> Let's fix that.

Good catch, but actually it goes a bit further:

"When GITS_CTLR.Enabled is written from 0 to 1 behavior is UNPREDICTABLE
if any of the following conditions are true:
· GITS_CBASER.Valid == 0.
...
"

So I think we need to check it upon setting CTLR.Enabled.
I did this in Xen, but forgot to fix this in KVM as well:
https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/arm/vgic-v3-its.c;hb=HEAD#l1164

Cheers,
Andre.

>
> Also rename cbaser local variable into cbaser_pa to avoid
> any confusion with the full register.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> ---
> virt/kvm/arm/vgic/vgic-its.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 60ecf91..720552c 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -1301,17 +1301,20 @@ static void vgic_mmio_write_its_cbaser(struct kvm *kvm, struct vgic_its *its,
> /* Must be called with the cmd_lock held. */
> static void vgic_its_process_commands(struct kvm *kvm, struct vgic_its *its)
> {
> - gpa_t cbaser;
> + gpa_t cbaser_pa;
> u64 cmd_buf[4];
>
> - /* Commands are only processed when the ITS is enabled. */
> - if (!its->enabled)
> + /*
> + * Commands are only processed when the ITS is enabled and
> + * CBASER is valid
> + */
> + if (!its->enabled || (!(its->cbaser & GITS_CBASER_VALID)))
> return;
>
> - cbaser = CBASER_ADDRESS(its->cbaser);
> + cbaser_pa = CBASER_ADDRESS(its->cbaser);
>
> while (its->cwriter != its->creadr) {
> - int ret = kvm_read_guest(kvm, cbaser + its->creadr,
> + int ret = kvm_read_guest(kvm, cbaser_pa + its->creadr,
> cmd_buf, ITS_CMD_SIZE);
> /*
> * If kvm_read_guest() fails, this could be due to the guest
>