[PATCH 3/4] arm64: fix hyp mode mismatch detection

[Marc Zyngier]

On 16/03/15 10:56, Mark Rutland wrote:
> On Fri, Mar 13, 2015 at 08:21:19PM +0000, Ard Biesheuvel wrote:
>> On 13 March 2015 at 17:14, Mark Rutland <mark.rutland at arm.com> wrote:
>>> Commit 828e9834e9a5b7e6 ("arm64: head: create a new function for setting
>>> the boot_cpu_mode flag") added BOOT_CPU_MODE_EL1, a nonzero value
>>> replacing uses of zero. However it failed to update __boot_cpu_mode
>>> appropriately.
>>>
>>> A CPU booted at EL2 writes BOOT_CPU_MODE_EL2 to __boot_cpu_mode[0], and
>>> a CPU booted at EL1 writes BOOT_CPU_MODE_EL1 to __boot_cpu_mode[1].
>>> Later is_hyp_mode_mismatched() determines there to be a mismatch if
>>> __boot_cpu_mode[0] != __boot_cpu_mode[1].
>>>
>>> If all CPUs are booted at EL1, __boot_cpu_mode[0] will be set to
>>> BOOT_CPU_MODE_EL1, but __boot_cpu_mode[1] will retain its initial value
>>> of zero, and is_hyp_mode_mismatched will erroneously determine that the
>>> boot modes are mismatched. This hasn't been a problem so far, but later
>>> patches which will make use of is_hyp_mode_mismatched() expect it to
>>> work correctly.
>>>
>>> This patch initialises __boot_cpu_mode[1] to BOOT_CPU_MODE_EL1, fixing
>>> the erroneous mismatch detection when all CPUs are booted at EL1.
>>>
>>
>> Maybe it's just me, but isn't it *much* easier to understand to
>> initialise both values to 0, and use 'both are non-zero' as the error
>> condition?
>> 'HYP mode available' would then be '__boot_cpu_mode[0] ==
>> BOOT_CPU_MODE_EL2 && __boot_cpu_mode[1] == 0'
> 
> I agree that change would make this easier to follow.
> 
> Marc, are you happy with Ard's proposed change?

Absolutely. If that makes it more obvious, please go for it.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...