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[RFC,32/43] KVM: PPC: Book3S HV P9: Restrict DSISR canary workaround to processors that require it

Message ID 20210622105736.633352-33-npiggin@gmail.com
State New
Headers show
Series KVM: PPC: Book3S HV P9: entry/exit optimisations round 1 | expand

Commit Message

Nicholas Piggin June 22, 2021, 10:57 a.m. UTC 
Use CPU_FTR_P9_RADIX_PREFETCH_BUG for this, to test for DD2.1 and below
processors.

-43 cycles (7178) POWER9 virt-mode NULL hcall

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kvm/book3s_hv.c          | 3 ++-
 arch/powerpc/kvm/book3s_hv_p9_entry.c | 6 ++++--
 2 files changed, 6 insertions(+), 3 deletions(-)
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Patch

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index a31397fde98e..ae528eb37792 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1523,7 +1523,8 @@  XXX benchmark guest exits
 		unsigned long vsid;
 		long err;
 
-		if (vcpu->arch.fault_dsisr == HDSISR_CANARY) {
+		if (cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG) &&
+		    unlikely(vcpu->arch.fault_dsisr == HDSISR_CANARY)) {
 			r = RESUME_GUEST; /* Just retry if it's the canary */
 			break;
 		}
diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index 9e58624566a4..b41be3d8f101 100644
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -656,9 +656,11 @@  int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 	 * HDSI which should correctly update the HDSISR the second time HDSI
 	 * entry.
 	 *
-	 * Just do this on all p9 processors for now.
+	 * The "radix prefetch bug" test can be used to test for this bug, as
+	 * it also exists fo DD2.1 and below.
 	 */
-	mtspr(SPRN_HDSISR, HDSISR_CANARY);
+	if (cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG))
+		mtspr(SPRN_HDSISR, HDSISR_CANARY);
 
 	mtspr(SPRN_SPRG0, vcpu->arch.shregs.sprg0);
 	mtspr(SPRN_SPRG1, vcpu->arch.shregs.sprg1);