On Wed, Feb 17, 2016 at 03:34:41PM +0000, Marc Zyngier wrote:
> When performing a MMIO access via a KVM IO bus, it is possible
> that the access will actually be out-of-bounds (the redistributor
> handlers do not cover the whole device, for example). In this case,
> we return an error code, which leads to escaping to userspace
> to handle it. Not that good.
Are all such OOB accesses on hardware simply RAZ/WI?
>
> Instead, let's just treat it like any other OOB access, by either
> ignoring the write, or by returning a bunch of zeroes.
>
> And let's keep the code quiet while we're at it, as nobody likes
> it when a guest can generate zillions on messages on the host's
> console...
>
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> ---
> virt/kvm/arm/vgic.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index 043032c..2358272 100644
> --- a/virt/kvm/arm/vgic.c
> +++ b/virt/kvm/arm/vgic.c
> @@ -830,8 +830,11 @@ static int vgic_handle_mmio_access(struct kvm_vcpu *vcpu,
> offset = addr - iodev->addr;
> range = vgic_find_range(iodev->reg_ranges, len, offset);
> if (unlikely(!range || !range->handle_mmio)) {
> - pr_warn("Unhandled access %d %08llx %d\n", is_write, addr, len);
> - return -ENXIO;
> + /* Treat an OOR access as RAZ/WI. */
> + if (!is_write)
> + memset(val, 0, len);
> + pr_debug("Unhandled access %d %08llx %d\n", is_write, addr, len);
> + return 0;
> }
>
> mmio.phys_addr = addr;
> --
> 2.1.4
>
This patch looks fine, but looking at that code, why do we write to
vcpu->run->mmio and call kvm_handle_mio_return in
vgic_handle_mmio_access and also in io_mem_abort?
After this patch you now have two return paths from this function that
both return 0, but only one of them does copies to vcpu->run and calls
the handle return function.
/me confused.
Thanks,
-Christoffer
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