Subject: Re: [PATCH v3] powerpc/64s: Improve local TLB flush for boot and MCE on POWER9

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Wed, 03 Jan 2018 12:34:34 +0530

Nicholas Piggin <[email-masked]> writes:

> There are several cases outside the normal address space management
> where a CPU's entire local TLB is to be flushed:
>
>   1. Booting the kernel, in case something has left stale entries in
>      the TLB (e.g., kexec).
>
>   2. Machine check, to clean corrupted TLB entries.
>
> One other place where the TLB is flushed, is waking from deep idle
> states. The flush is a side-effect of calling ->cpu_restore with the
> intention of re-setting various SPRs. The flush itself is unnecessary
> because in the first case, the TLB should not acquire new corrupted
> TLB entries as part of sleep/wake (though they may be lost).
>
> This type of TLB flush is coded inflexibly, several times for each CPU
> type, and they have a number of problems with ISA v3.0B:
>
> - The current radix mode of the MMU is not taken into account, it is
>   always done as a hash flushn For IS=2 (LPID-matching flush from host)
>   and IS=3 with HV=0 (guest kernel flush), tlbie(l) is undefined if
>   the R field does not match the current radix mode.
>
> - ISA v3.0B hash must flush the partition and process table caches as
>   well.
>
> - ISA v3.0B radix must flush partition and process scoped translations,
>   partition and process table caches, and also the page walk cache.
>
> So consolidate the flushing code and implement it in C and inline asm
> under the mm/ directory with the rest of the flush code. Add ISA v3.0B
> cases for radix and hash, and use the radix flush in radix environment.
>
> Provide a way for IS=2 (LPID flush) to specify the radix mode of the
> partition. Have KVM pass in the radix mode of the guest.
>
> Take out the flushes from early cputable/dt_cpu_ftrs detection hooks,
> and move it later in the boot process after, the MMU registers are set
> up and before relocation is first turned on.
>
> The TLB flush is no longer called when restoring from deep idle states.
> This was not be done as a separate step because booting secondaries
> uses the same cpu_restore as idle restore, which needs the TLB flush.
>
> Signed-off-by: Nicholas Piggin <[email-masked]>

......

> diff --git a/arch/powerpc/kvm/book3s_hv_ras.c b/arch/powerpc/kvm/book3s_hv_ras.c
> index c356f9a40b24..e61066bb6725 100644
> --- a/arch/powerpc/kvm/book3s_hv_ras.c
> +++ b/arch/powerpc/kvm/book3s_hv_ras.c
> @@ -87,8 +87,7 @@ static long kvmppc_realmode_mc_power7(struct kvm_vcpu *vcpu)
>  				   DSISR_MC_SLB_PARITY | DSISR_MC_DERAT_MULTI);
>  		}
>  		if (dsisr & DSISR_MC_TLB_MULTI) {
> -			if (cur_cpu_spec && cur_cpu_spec->flush_tlb)
> -				cur_cpu_spec->flush_tlb(TLB_INVAL_SCOPE_LPID);
> +			tlbiel_all_lpid(vcpu->kvm->arch.radix);

Why use vcpu->kvm-arch.radix? why not TLB_INVAL_SCOPE_LPID?

>  			dsisr &= ~DSISR_MC_TLB_MULTI;
>  		}
>  		/* Any other errors we don't understand? */
> @@ -105,8 +104,7 @@ static long kvmppc_realmode_mc_power7(struct kvm_vcpu *vcpu)
>  		reload_slb(vcpu);
>  		break;
>  	case SRR1_MC_IFETCH_TLBMULTI:
> -		if (cur_cpu_spec && cur_cpu_spec->flush_tlb)
> -			cur_cpu_spec->flush_tlb(TLB_INVAL_SCOPE_LPID);
> +		tlbiel_all_lpid(vcpu->kvm->arch.radix);
>  		break;
>  	default:
>  		handled = 0;

-aneesh