Nicholas Piggin <npiggin@xxxxxxxxx> writes:
> LPCR[HDICE]=0 suppresses hypervisor decrementer exceptions on some
> processors, so it must be enabled before HDEC is set.
>
> Rather than set it in the host LPCR then setting HDEC, move the HDEC
> update to after the guest MMU context (including LPCR) is loaded.
> There shouldn't be much concern with delaying HDEC by some 10s or 100s
> of nanoseconds by setting it a bit later.
>
> Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Reviewed-by: Fabiano Rosas <farosas@xxxxxxxxxxxxx>
> ---
> arch/powerpc/kvm/book3s_hv.c | 19 +++++++------------
> 1 file changed, 7 insertions(+), 12 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 1f2ba8955c6a..ffde1917ab68 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -3505,20 +3505,9 @@ static int kvmhv_load_hv_regs_and_go(struct kvm_vcpu *vcpu, u64 time_limit,
> host_dawrx1 = mfspr(SPRN_DAWRX1);
> }
>
> - /*
> - * P8 and P9 suppress the HDEC exception when LPCR[HDICE] = 0,
> - * so set HDICE before writing HDEC.
> - */
> - mtspr(SPRN_LPCR, kvm->arch.host_lpcr | LPCR_HDICE);
> - isync();
> -
> hdec = time_limit - mftb();
> - if (hdec < 0) {
> - mtspr(SPRN_LPCR, kvm->arch.host_lpcr);
> - isync();
> + if (hdec < 0)
> return BOOK3S_INTERRUPT_HV_DECREMENTER;
> - }
> - mtspr(SPRN_HDEC, hdec);
>
> if (vc->tb_offset) {
> u64 new_tb = mftb() + vc->tb_offset;
> @@ -3564,6 +3553,12 @@ static int kvmhv_load_hv_regs_and_go(struct kvm_vcpu *vcpu, u64 time_limit,
>
> switch_mmu_to_guest_radix(kvm, vcpu, lpcr);
>
> + /*
> + * P9 suppresses the HDEC exception when LPCR[HDICE] = 0,
> + * so set guest LPCR (with HDICE) before writing HDEC.
> + */
> + mtspr(SPRN_HDEC, hdec);
> +
> mtspr(SPRN_SRR0, vcpu->arch.shregs.srr0);
> mtspr(SPRN_SRR1, vcpu->arch.shregs.srr1);
