[PATCH v4 02/46] KVM: PPC: Book3S HV: Add a function to filter guest LPCR bits

[Nicholas Piggin]

Excerpts from Nicholas Piggin's message of April 1, 2021 7:32 pm:
> Excerpts from Paul Mackerras's message of March 31, 2021 2:08 pm:
>> On Tue, Mar 23, 2021 at 11:02:21AM +1000, Nicholas Piggin wrote:
>>> Guest LPCR depends on hardware type, and future changes will add
>>> restrictions based on errata and guest MMU mode. Move this logic
>>> to a common function and use it for the cases where the guest
>>> wants to update its LPCR (or the LPCR of a nested guest).
>> 
>> [snip]
>> 
>>> @@ -4641,8 +4662,9 @@ void kvmppc_update_lpcr(struct kvm *kvm, unsigned long lpcr, unsigned long mask)
>>>  		struct kvmppc_vcore *vc = kvm->arch.vcores[i];
>>>  		if (!vc)
>>>  			continue;
>>> +
>>>  		spin_lock(&vc->lock);
>>> -		vc->lpcr = (vc->lpcr & ~mask) | lpcr;
>>> +		vc->lpcr = kvmppc_filter_lpcr_hv(vc, (vc->lpcr & ~mask) | lpcr);
>> 
>> This change seems unnecessary, since kvmppc_update_lpcr is called only
>> to update MMU configuration bits, not as a result of any action by
>> userspace or a nested hypervisor.  It's also beyond the scope of what
>> was mentioned in the commit message.
> 
> I didn't think it was outside the spirit of the patch, but yes
> only the guest update LPCR case was enumerated. Would it be more 
> consistent to add it to the changelog and leave it in here or would
> you prefer it left out until there is a real use?

On second thoughts, I already left at least one other place without
such a check, so I now tend to agree with you. But I instead added
a test that just ensures the host is not out of synch with itself in
terms of what it can set the LPCR to.

Thanks,
Nick