Re: [PATCH v3] xen/arm: Correctly support WARN_ON

[Julien Grall <julien.grall@linaro.org>]

Hi Ian,

On 22/09/2014 16:29, Ian Campbell wrote:
> On Wed, 2014-09-10 at 16:33 -0700, Julien Grall wrote:
>> +#ifdef CONFIG_ARM_64
>> +static void do_trap_brk(struct cpu_user_regs *regs, union hsr hsr)
>> +{
>> +    /* HCR_EL2.TGE and MDCR_EL2.TDE are not set so we never receive
>> +     * software breakpoint exception for EL1 and EL0 here
>> +     */
>> +    /* It's not possible to use BUG_ON here, because we would recurse */
>> +    if ( unlikely(READ_SYSREG(HCR_EL2) & HCR_TGE) ||
>> +         unlikely(READ_SYSREG(MDCR_EL2) & HDCR_TDE) )
>> +        panic("Unable to handle brk exception from EL1/EL0");
>
> Either of those bits being set doesn't imply that *this* trap came from
> EL1/EL0.
>
> The correct check would be BUG_ON(!hyp_mode(regs)) which I think won't
> recurse because the resulting BRK will pass the check the second time,
> although if you want to if (!hyp_mode(regs)) panic(...) instead that's
> fine too.

In fact, I haven't though this way. The BUG_ON(!hyp_mode(regs)) will 
definitely works here.

I will send a new version with this change and the typoes fixed.

Regards,



-- 
Julien Grall