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[RFC,09/43] KVM: PPC: Book3S HV: Don't always save PMU for guest capable of nesting

Message ID 20210622105736.633352-10-npiggin@gmail.com (mailing list archive)
State Not Applicable
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Series KVM: PPC: Book3S HV P9: entry/exit optimisations round 1 | expand
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Commit Message

Nicholas Piggin June 22, 2021, 10:57 a.m. UTC 
Revert the workaround added by commit 63279eeb7f93a ("KVM: PPC: Book3S
HV: Always save guest pmu for guest capable of nesting").

Nested capable guests running with the earlier commit ("KVM: PPC: Book3S
HV Nested: Indicate guest PMU in-use in VPA") will now indicate the PMU
in-use status of their guests, which means the parent does not need to
unconditionally save the PMU for nested capable guests.

This will cause the PMU to break for nested guests when running older
nested hypervisor guests under a kernel with this change. It's unclear
there's an easy way to avoid that, so this could wait for a release or
so for the fix to filter into stable kernels.

-134 cycles (8982) POWER9 virt-mode NULL hcall

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kvm/book3s_hv.c | 2 --
 1 file changed, 2 deletions(-)
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Patch

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index ed713f49fbd5..1f30f98b09d1 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -3901,8 +3901,6 @@  static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
 		vcpu->arch.vpa.dirty = 1;
 		save_pmu = lp->pmcregs_in_use;
 	}
-	/* Must save pmu if this guest is capable of running nested guests */
-	save_pmu |= nesting_enabled(vcpu->kvm);
 
 	kvmhv_save_guest_pmu(vcpu, save_pmu);
 #ifdef CONFIG_PPC_PSERIES