Re: [PATCH RFC V3 7/9] x86/entry: Preserve PKRS MSR across exceptions

[Dave Hansen]

On 10/14/20 8:46 PM, Ira Weiny wrote:
> On Tue, Oct 13, 2020 at 11:52:32AM -0700, Dave Hansen wrote:
>> On 10/9/20 12:42 PM, ira.weiny@xxxxxxxxx wrote:
>>> @@ -341,6 +341,9 @@ noinstr void irqentry_enter(struct pt_regs *regs, irqentry_state_t *state)
>>>  	/* Use the combo lockdep/tracing function */
>>>  	trace_hardirqs_off();
>>>  	instrumentation_end();
>>> +
>>> +done:
>>> +	irq_save_pkrs(state);
>>>  }
>> One nit: This saves *and* sets PKRS.  It's not obvious from the call
>> here that PKRS is altered at this site.  Seems like there could be a
>> better name.
>>
>> Even if we did:
>>
>> 	irq_save_set_pkrs(state, INIT_VAL);
>>
>> It would probably compile down to the same thing, but be *really*
>> obvious what's going on.
> I suppose that is true.  But I think it is odd having a parameter which is the
> same for every call site.

Well, it depends on what you optimize for.  I'm trying to optimize for
the code being understood quickly the first time someone reads it.  To
me, that's more important than minimizing the number of function
parameters (which are essentially free).