[RFC PATCH 4/5] KVM: PPC: Book3S HV: handle need_tlb_flush in C before low-level guest entry

[Benjamin Herrenschmidt]

On Tue, 2018-04-10 at 22:48 +1000, Nicholas Piggin wrote:
>  
> +       /*
> +        * Do we need to flush the TLB for the LPAR? (see TLB comment above)
> +         * On POWER9, individual threads can come in here, but the
> +         * TLB is shared between the 4 threads in a core, hence
> +         * invalidating on one thread invalidates for all.
> +         * Thus we make all 4 threads use the same bit here.
> +         */

This might be true of P9 implementation but isn't architecturally
correct. From an ISA perspective, the threads could have dedicatd
tagged TLB entries. Do we need to be careful here vs. backward
compatiblity ?

Also this won't flush ERAT entries for another thread afaik.

> +       tmp = pcpu;
> +       if (cpu_has_feature(CPU_FTR_ARCH_300))
> +               tmp &= ~0x3UL;
> +       if (cpumask_test_cpu(tmp, &vc->kvm->arch.need_tlb_flush)) {
> +               if (kvm_is_radix(vc->kvm))
> +                       radix__local_flush_tlb_lpid(vc->kvm->arch.lpid);
> +               else
> +                       hash__local_flush_tlb_lpid(vc->kvm->arch.lpid);
> +               /* Clear the bit after the TLB flush */
> +               cpumask_clear_cpu(tmp, &vc->kvm->arch.need_tlb_flush);
> +       }
> +