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KVM: PPC: Book3S HV P9: Improve mtmsrd scheduling by delaying MSR[EE] disable

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Moving the mtmsrd after the host SPRs are saved and before the guest
SPRs start to be loaded can prevent an SPR scoreboard stall (because
the mtmsrd is L=1 type which does not cause context synchronisation.

This is also now more convenient to combined with the mtmsrd L=0
instruction to enable facilities just below, but that is not done yet.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-21-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2021-11-23 19:51:58 +10:00 committed by Michael Ellerman
parent 34e119c96b
commit 2251fbe763
1 changed files with 18 additions and 5 deletions
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23
arch/powerpc/kvm/book3s_hv.c
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@ -4169,6 +4169,18 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
save_p9_host_os_sprs(&host_os_sprs); save_p9_host_os_sprs(&host_os_sprs);
/*
* This could be combined with MSR[RI] clearing, but that expands
* the unrecoverable window. It would be better to cover unrecoverable
* with KVM bad interrupt handling rather than use MSR[RI] at all.
*
* Much more difficult and less worthwhile to combine with IR/DR
* disable.
*/
hard_irq_disable();
if (lazy_irq_pending())
return 0;
/* MSR bits may have been cleared by context switch */ /* MSR bits may have been cleared by context switch */
msr = 0; msr = 0;
if (IS_ENABLED(CONFIG_PPC_FPU)) if (IS_ENABLED(CONFIG_PPC_FPU))
@ -4680,6 +4692,7 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
struct kvmppc_vcore *vc; struct kvmppc_vcore *vc;
struct kvm *kvm = vcpu->kvm; struct kvm *kvm = vcpu->kvm;
struct kvm_nested_guest *nested = vcpu->arch.nested; struct kvm_nested_guest *nested = vcpu->arch.nested;
unsigned long flags;
trace_kvmppc_run_vcpu_enter(vcpu); trace_kvmppc_run_vcpu_enter(vcpu);
@ -4723,11 +4736,11 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
if (kvm_is_radix(kvm)) if (kvm_is_radix(kvm))
kvmppc_prepare_radix_vcpu(vcpu, pcpu); kvmppc_prepare_radix_vcpu(vcpu, pcpu);
local_irq_disable(); /* flags save not required, but irq_pmu has no disable/enable API */
hard_irq_disable(); powerpc_local_irq_pmu_save(flags);
if (signal_pending(current)) if (signal_pending(current))
goto sigpend; goto sigpend;
if (lazy_irq_pending() || need_resched() || !kvm->arch.mmu_ready) if (need_resched() || !kvm->arch.mmu_ready)
goto out; goto out;
if (!nested) { if (!nested) {
@ -4795,7 +4808,7 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
} }
vtime_account_guest_exit(); vtime_account_guest_exit();
local_irq_enable(); powerpc_local_irq_pmu_restore(flags);
cpumask_clear_cpu(pcpu, &kvm->arch.cpu_in_guest); cpumask_clear_cpu(pcpu, &kvm->arch.cpu_in_guest);
@ -4853,7 +4866,7 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
run->exit_reason = KVM_EXIT_INTR; run->exit_reason = KVM_EXIT_INTR;
vcpu->arch.ret = -EINTR; vcpu->arch.ret = -EINTR;
out: out:
local_irq_enable(); powerpc_local_irq_pmu_restore(flags);
preempt_enable(); preempt_enable();
goto done; goto done;
} }