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

[Paul Mackerras]

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.

>  	/* 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?

Paul.