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

Auger Eric
2017-10-06T15:29:16Z

Hi Andre,

On 06/10/2017 16:38, Andre Przywara wrote:
> 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

OK. I will add this check.

Thanks

Eric
>
> 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
>>