[PATCH v4 04/46] KVM: PPC: Book3S HV: Prevent radix guests from setting LPCR[TC]

[Nicholas Piggin]

Excerpts from Paul Mackerras's message of March 31, 2021 2:34 pm:
> On Tue, Mar 23, 2021 at 11:02:23AM +1000, Nicholas Piggin wrote:
>> This bit only applies to hash partitions.
>> 
>> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
>> ---
>>  arch/powerpc/kvm/book3s_hv.c        | 6 ++++++
>>  arch/powerpc/kvm/book3s_hv_nested.c | 3 +--
>>  2 files changed, 7 insertions(+), 2 deletions(-)
>> 
>> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
>> index c5de7e3f22b6..1ffb0902e779 100644
>> --- a/arch/powerpc/kvm/book3s_hv.c
>> +++ b/arch/powerpc/kvm/book3s_hv.c
>> @@ -1645,6 +1645,12 @@ static int kvm_arch_vcpu_ioctl_set_sregs_hv(struct kvm_vcpu *vcpu,
>>   */
>>  unsigned long kvmppc_filter_lpcr_hv(struct kvmppc_vcore *vc, unsigned long lpcr)
>>  {
>> +	struct kvm *kvm = vc->kvm;
>> +
>> +	/* LPCR_TC only applies to HPT guests */
>> +	if (kvm_is_radix(kvm))
>> +		lpcr &= ~LPCR_TC;
> 
> I'm not sure I see any benefit from this, and it is a little extra
> complexity.

Principle of allowing a guest to mess with as little HV state as 
possible (but not littler), which I think is a good one to follow.

> 
>>  	/* On POWER8 and above, userspace can modify AIL */
>>  	if (!cpu_has_feature(CPU_FTR_ARCH_207S))
>>  		lpcr &= ~LPCR_AIL;
>> diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
>> index f7b441b3eb17..851e3f527eb2 100644
>> --- a/arch/powerpc/kvm/book3s_hv_nested.c
>> +++ b/arch/powerpc/kvm/book3s_hv_nested.c
>> @@ -140,8 +140,7 @@ static void sanitise_hv_regs(struct kvm_vcpu *vcpu, struct hv_guest_state *hr)
>>  	/*
>>  	 * Don't let L1 change LPCR bits for the L2 except these:
>>  	 */
>> -	mask = LPCR_DPFD | LPCR_ILE | LPCR_TC | LPCR_AIL | LPCR_LD |
>> -		LPCR_LPES | LPCR_MER;
>> +	mask = LPCR_DPFD | LPCR_ILE | LPCR_AIL | LPCR_LD | LPCR_LPES | LPCR_MER;
> 
> Doesn't this make it completely impossible to set TC for any guest?

Argh, yes Fabiano pointed this out in an earlier rev and I didn't
fix this hunk after adding the filter bit. Thanks.

Thanks,
Nick