On 2019-12-16 15:33, Peter Maydell wrote:
On Thu, 12 Dec 2019 at 17:33, Andrew Jones <drjo...@redhat.com>
wrote:
Userspace that wants to set KVM_REG_ARM_TIMER_CNT should beware that
the KVM register ID is not correct. This cannot be fixed because
it's
UAPI and if the UAPI headers are used then it can't be a problem.
However, if a userspace attempts to create the ID themselves from
the
register's specification, then they will get KVM_REG_ARM_TIMER_CVAL
instead, as the _CNT and _CVAL definitions have their register
parameters swapped.
So, to be clear, you mean that:
(1) the kernel headers say:
/* EL0 Virtual Timer Registers */
#define KVM_REG_ARM_TIMER_CTL ARM64_SYS_REG(3, 3, 14, 3, 1)
#define KVM_REG_ARM_TIMER_CNT ARM64_SYS_REG(3, 3, 14, 3, 2)
#define KVM_REG_ARM_TIMER_CVAL ARM64_SYS_REG(3, 3, 14, 0, 2)
(2) some of the RHSes of these are wrong
(3) but the kernel internally is using the same 'wrong' value, so
userspace also needs to use that value, ie trust the #defined name
rather than manufacturing one ?
That's awkward. I think it would be worth at least having a kernel
patch to add a comment clearly documenting this bug.
(This error seems to only be in the 64-bit ABI, not 32-bit.)
Yeah, this is pretty bad. I wonder how we managed not to notice
this for so long... :-(.
Andrew, could you please write a patch documenting this (both in
the UAPI headers and in the documentation)?
Thanks,
M.
--
Jazz is not dead. It just smells funny...
