Re: [PATCH v2 for-4.14] x86/livepatch: Make livepatching compatible with CET Shadow Stacks

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/06/2020 16:07, Ross Lagerwall wrote:
> On 2020-06-26 15:46, Andrew Cooper wrote:
>> On 26/06/2020 15:26, Jan Beulich wrote:
>>> On 26.06.2020 15:59, Ross Lagerwall wrote:
>>>> On 2020-06-26 13:24, Andrew Cooper wrote:
>>>>> @@ -56,18 +57,48 @@ int arch_livepatch_safety_check(void)
>>>>>      return -EBUSY;
>>>>>  }
>>>>>  
>>>>> -int arch_livepatch_quiesce(void)
>>>>> +int noinline arch_livepatch_quiesce(void)
>>>>>  {
>>>>> +    /* If Shadow Stacks are in use, disable CR4.CET so we can modify 
>>>>> CR0.WP. */
>>>>> +    if ( cpu_has_xen_shstk )
>>>> Should this be:
>>>>     if ( IS_ENABLED(CONFIG_XEN_SHSTK) && cpu_has_xen_shstk )
>>>>
>>>> to match arch_livepatch_revive?
>>> While it may look a little asymmetric, I think it's preferable
>>> to is IS_ENABLED() only where really needed, i.e. here it
>>> guarding code that otherwise may not build.
>> The reason for the asymmetry is because of the asm() block, which needs
>> compiling out when we detect that we don't have a compatible assembler.
>>
> In that case,
>
> Reviewed-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>

Thanks.  I've decided to clean this up in the (growing) series of 4.15
changes.

~Andrew