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 Thu, 01 Apr 2021 02:32:37 -0700 (PDT)
Date: Thu, 01 Apr 2021 19:32:32 +1000
From: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v4 02/46] KVM: PPC: Book3S HV: Add a function to filter
 guest LPCR bits
To: Paul Mackerras <paulus@ozlabs.org>
References: <20210323010305.1045293-1-npiggin@gmail.com>
 <20210323010305.1045293-3-npiggin@gmail.com>
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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).
>=20
> [snip]
>=20
>> @@ -4641,8 +4662,9 @@ void kvmppc_update_lpcr(struct kvm *kvm, unsigned =
long lpcr, unsigned long mask)
>>  		struct kvmppc_vcore *vc =3D kvm->arch.vcores[i];
>>  		if (!vc)
>>  			continue;
>> +
>>  		spin_lock(&vc->lock);
>> -		vc->lpcr =3D (vc->lpcr & ~mask) | lpcr;
>> +		vc->lpcr =3D kvmppc_filter_lpcr_hv(vc, (vc->lpcr & ~mask) | lpcr);
>=20
> 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=20
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?

The intention is a single location to add some of these things
(handwaving: say tlbie doesn't work on some chip and we want to=20
emulate it for old guests we could clear GTSE).

Thanks,
Nick