Re: [PATCH v2 02/10] KVM: arm/arm64: vgic-its: Always allow clearing GITS_CREADR/CWRITER

Christoffer Dall
2017-10-13T11:44:15Z

On Fri, Oct 06, 2017 at 05:29:02PM +0200, Auger Eric wrote:
> Hi,
>
> On 06/10/2017 16:37, Andre Przywara wrote:
> > Hi,
> >
> > On 27/09/17 14:28, Eric Auger wrote:
> >> If the GITS_CBASER Size field is 0, which can correspond to a
> >> reset value, the userspace fails to set the GITS_CREADR/CWRITER
> >> offsets to 0. This failure is not justified.
> >>
> >> Let's allow this setting which can also correspond to a reset value.
> >
> > But the GITS_CBASER size field has a +1 encoding, so can never be 0, if
> > I understand the manual (and ITS_CMD_BUFFER_SIZE) correctly.
> Oh OK, you're. I missed that. I would have sworn I've seen that failure
> but I must have misinterpreted it.
>

What is CWRITER is written to a brand new ITS before the CBASER is
written?

I don't see us initializing the cbaser field anywhere?

Thanks,
-Christoffer

> >
> > What am I missing here?
> >
> > Cheers,
> > Andre.
> >
> >> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> >>
> >> ---
> >>
> >> need to CC stable
> >> ---
> >> virt/kvm/arm/vgic/vgic-its.c | 4 ++--
> >> 1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> >> index fbbc97b..76bed2d 100644
> >> --- a/virt/kvm/arm/vgic/vgic-its.c
> >> +++ b/virt/kvm/arm/vgic/vgic-its.c
> >> @@ -1329,7 +1329,7 @@ static void vgic_mmio_write_its_cwriter(struct kvm *kvm, struct vgic_its *its,
> >>
> >> reg = update_64bit_reg(its->cwriter, addr & 7, len, val);
> >> reg = ITS_CMD_OFFSET(reg);
> >> - if (reg >= ITS_CMD_BUFFER_SIZE(its->cbaser)) {
> >> + if (reg && reg >= ITS_CMD_BUFFER_SIZE(its->cbaser)) {
> >> mutex_unlock(&its->cmd_lock);
> >> return;
> >> }
> >> @@ -1370,7 +1370,7 @@ static int vgic_mmio_uaccess_write_its_creadr(struct kvm *kvm,
> >> }
> >>
> >> cmd_offset = ITS_CMD_OFFSET(val);
> >> - if (cmd_offset >= ITS_CMD_BUFFER_SIZE(its->cbaser)) {
> >> + if (cmd_offset && cmd_offset >= ITS_CMD_BUFFER_SIZE(its->cbaser)) {
> >> ret = -EINVAL;
> >> goto out;
> >> }
> >>