Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter

[Ingo Molnar]

* Fenghua Yu <fenghua.yu@xxxxxxxxx> wrote:

> > This feature MUST be default enabled, otherwise everything will 
> > be/remain broken and we'll end up in the situation where you can't 
> > use it even if you wanted to.
> 
> The usage scope of this patch set is largely reduced to only real time. 
> The long split lock processing time (>1000 cycles) cannot be tolerated 
> by real time.
> 
> Real time customers do want to use this feature to detect the fatal 
> split lock error. They don't want any split lock issue from BIOS/EFI/ 
> firmware/kerne/drivers/user apps.
> 
> Real time can enable the feature (set bit 29 in TEST_CTRL MSR) in BIOS 
> and don't need OS to enable it. But, #AC handler cannot handle split 
> lock in the kernel and will return to the faulting instruction and 
> re-enter #AC. So current #AC handler doesn't provide useful information 
> for the customers. That's why we add the new #AC handler in this patch 
> set.

Immaterial - for this feature to be useful it must be default-enabled, 
with reasonable quirk knobs offered to people who happen to be bitten by 
such bugs and cannot fix the software.

But default-enabled is a must-have, as Peter said.

Thanks,

	Ingo