On 2021-01-12 17:28, Alexandru Elisei wrote:
Hi Eric,
On 12/12/20 6:50 PM, Eric Auger wrote:
Commit 23bde34771f1 ("KVM: arm64: vgic-v3: Drop the
reporting of GICR_TYPER.Last for userspace") temporarily fixed
a bug identified when attempting to access the GICR_TYPER
register before the redistributor region setting but dropped
the support of the LAST bit. This patch restores its
support (if the redistributor region was set) while keeping the
code safe.
If I understand your patch correctly, it is possible for the
GICR_TYPER.Last bit
to be transiently 1 if the register is accessed before all the
redistributors
regions have been configured.
Arm IHI 0069F states that accesses to the GICR_TYPER register are RO. I
haven't
found exactly what RO means (please point me to the definition if you
find it in
the architecture!), but I assume it means read-only and I'm not sure
how correct
(from an architectural point of view) it is for two subsequent reads of
this
register to return different values. Maybe Marc can shed some light on
this.
RO = Read-Only indeed. Not sure that's documented anywhere in the
architecture,
but this is enough of a well known acronym that even the ARM ARM doesn't
feel
the need to invent a new definition for it.
As for your concern, I don't think it is a problem to return different
values
if the HW has changed in between. This may need to be documented though.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
