Re: [PATCH v5 3/9] x86/split_lock: Re-define the kernel param option for split_lock_detect

[Sean Christopherson]

On Tue, Mar 24, 2020 at 11:40:18AM +0100, Thomas Gleixner wrote:
> Xiaoyao Li <xiaoyao.li@xxxxxxxxx> writes:
> > On 3/24/2020 1:10 AM, Thomas Gleixner wrote:
> >> Xiaoyao Li <xiaoyao.li@xxxxxxxxx> writes:
> >> 
> >>> Change sld_off to sld_disable, which means disabling feature split lock
> >>> detection and it cannot be used in kernel nor can kvm expose it guest.
> >>> Of course, the X86_FEATURE_SPLIT_LOCK_DETECT is not set.
> >>>
> >>> Add a new optioin sld_kvm_only, which means kernel turns split lock
> >>> detection off, but kvm can expose it to guest.
> >> 
> >> What's the point of this? If the host is not clean, then you better fix
> >> the host first before trying to expose it to guests.
> >
> > It's not about whether or not host is clean. It's for the cases that 
> > users just don't want it enabled on host, to not break the applications 
> > or drivers that do have split lock issue.
> 
> It's very much about whether the host is split lock clean.
> 
> If your host kernel is not, then this wants to be fixed first. If your
> host application is broken, then either fix it or use "warn".

The "kvm only" option was my suggestion.  The thought was to provide a way
for users to leverage KVM to debug/test kernels without having to have a
known good kernel and/or to minimize the risk of crashing their physical
system.  E.g. debug a misbehaving driver by assigning its associated device
to a guest.