KVM: PPC: Book3S HV P9: Remove subcore HMI handling

On POWER9 and newer, rather than the complex HMI synchronisation and
subcore state, have each thread un-apply the guest TB offset before
calling into the early HMI handler.

This allows the subcore state to be avoided, including subcore enter
/ exit guest, which includes an expensive divide that shows up
slightly in profiles.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-54-npiggin@gmail.com

1 files changed, 54 insertions, 0 deletions

diff --git a/arch/powerpc/kvm/book3s_hv_ras.c b/arch/powerpc/kvm/book3s_hv_ras.c
index d4bca93b79f6..ccfd96965630 100644
--- a/arch/powerpc/kvm/book3s_hv_ras.c
+++ b/arch/powerpc/kvm/book3s_hv_ras.c
@@ -136,6 +136,60 @@ void kvmppc_realmode_machine_check(struct kvm_vcpu *vcpu)
 	vcpu->arch.mce_evt = mce_evt;
 }
 
+
+long kvmppc_p9_realmode_hmi_handler(struct kvm_vcpu *vcpu)
+{
+	struct kvmppc_vcore *vc = vcpu->arch.vcore;
+	long ret = 0;
+
+	/*
+	 * Unapply and clear the offset first. That way, if the TB was not
+	 * resynced then it will remain in host-offset, and if it was resynced
+	 * then it is brought into host-offset. Then the tb offset is
+	 * re-applied before continuing with the KVM exit.
+	 *
+	 * This way, we don't need to actually know whether not OPAL resynced
+	 * the timebase or do any of the complicated dance that the P7/8
+	 * path requires.
+	 */
+	if (vc->tb_offset_applied) {
+		u64 new_tb = mftb() - vc->tb_offset_applied;
+		mtspr(SPRN_TBU40, new_tb);
+		if ((mftb() & 0xffffff) < (new_tb & 0xffffff)) {
+			new_tb += 0x1000000;
+			mtspr(SPRN_TBU40, new_tb);
+		}
+		vc->tb_offset_applied = 0;
+	}
+
+	local_paca->hmi_irqs++;
+
+	if (hmi_handle_debugtrig(NULL) >= 0) {
+		ret = 1;
+		goto out;
+	}
+
+	if (ppc_md.hmi_exception_early)
+		ppc_md.hmi_exception_early(NULL);
+
+out:
+	if (vc->tb_offset) {
+		u64 new_tb = mftb() + vc->tb_offset;
+		mtspr(SPRN_TBU40, new_tb);
+		if ((mftb() & 0xffffff) < (new_tb & 0xffffff)) {
+			new_tb += 0x1000000;
+			mtspr(SPRN_TBU40, new_tb);
+		}
+		vc->tb_offset_applied = vc->tb_offset;
+	}
+
+	return ret;
+}
+
+/*
+ * The following subcore HMI handling is all only for pre-POWER9 CPUs.
+ */
+
 /* Check if dynamic split is in force and return subcore size accordingly. */
 static inline int kvmppc_cur_subcore_size(void)
 {