KVM: PPC: Book3S HV: Remove support for running HPT guest on RPT host without mixed mode support

This reverts much of commit c01015091a770 ("KVM: PPC: Book3S HV: Run HPT
guests on POWER9 radix hosts"), which was required to run HPT guests on
RPT hosts on early POWER9 CPUs without support for "mixed mode", which
meant the host could not run with MMU on while guests were running.

This code has some corner case bugs, e.g., when the guest hits a machine
check or HMI the primary locks up waiting for secondaries to switch LPCR
to host, which they never do. This could all be fixed in software, but
most CPUs in production have mixed mode support, and those that don't
are believed to be all in installations that don't use this capability.
So simplify things and remove support.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

1 files changed, 12 insertions, 44 deletions

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index dffbfd1ab47b..89c686c17f06 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -134,7 +134,7 @@ static inline bool nesting_enabled(struct kvm *kvm)
 }
 
 /* If set, the threads on each CPU core have to be in the same MMU mode */
-static bool no_mixing_hpt_and_radix;
+static bool no_mixing_hpt_and_radix __read_mostly;
 
 static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu);
 
@@ -2890,11 +2890,6 @@ static bool can_dynamic_split(struct kvmppc_vcore *vc, struct core_info *cip)
 	if (one_vm_per_core && vc->kvm != cip->vc[0]->kvm)
 		return false;
 
-	/* Some POWER9 chips require all threads to be in the same MMU mode */
-	if (no_mixing_hpt_and_radix &&
-	    kvm_is_radix(vc->kvm) != kvm_is_radix(cip->vc[0]->kvm))
-		return false;
-
 	if (n_threads < cip->max_subcore_threads)
 		n_threads = cip->max_subcore_threads;
 	if (!subcore_config_ok(cip->n_subcores + 1, n_threads))
@@ -2933,6 +2928,9 @@ static void prepare_threads(struct kvmppc_vcore *vc)
 	for_each_runnable_thread(i, vcpu, vc) {
 		if (signal_pending(vcpu->arch.run_task))
 			vcpu->arch.ret = -EINTR;
+		else if (no_mixing_hpt_and_radix &&
+			 kvm_is_radix(vc->kvm) != radix_enabled())
+			vcpu->arch.ret = -EINVAL;
 		else if (vcpu->arch.vpa.update_pending ||
 			 vcpu->arch.slb_shadow.update_pending ||
 			 vcpu->arch.dtl.update_pending)
@@ -3138,7 +3136,6 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
 	int controlled_threads;
 	int trap;
 	bool is_power8;
-	bool hpt_on_radix;
 
 	/*
 	 * Remove from the list any threads that have a signal pending
@@ -3171,11 +3168,8 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
 	 * this is a HPT guest on a radix host machine where the
 	 * CPU threads may not be in different MMU modes.
 	 */
-	hpt_on_radix = no_mixing_hpt_and_radix && radix_enabled() &&
-		!kvm_is_radix(vc->kvm);
-	if (((controlled_threads > 1) &&
-	     ((vc->num_threads > threads_per_subcore) || !on_primary_thread())) ||
-	    (hpt_on_radix && vc->kvm->arch.threads_indep)) {
+	if ((controlled_threads > 1) &&
+	    ((vc->num_threads > threads_per_subcore) || !on_primary_thread())) {
 		for_each_runnable_thread(i, vcpu, vc) {
 			vcpu->arch.ret = -EBUSY;
 			kvmppc_remove_runnable(vc, vcpu);
@@ -3243,7 +3237,7 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
 	is_power8 = cpu_has_feature(CPU_FTR_ARCH_207S)
 		&& !cpu_has_feature(CPU_FTR_ARCH_300);
 
-	if (split > 1 || hpt_on_radix) {
+	if (split > 1) {
 		sip = &split_info;
 		memset(&split_info, 0, sizeof(split_info));
 		for (sub = 0; sub < core_info.n_subcores; ++sub)
@@ -3265,13 +3259,6 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
 			split_info.subcore_size = subcore_size;
 		} else {
 			split_info.subcore_size = 1;
-			if (hpt_on_radix) {
-				/* Use the split_info for LPCR/LPIDR changes */
-				split_info.lpcr_req = vc->lpcr;
-				split_info.lpidr_req = vc->kvm->arch.lpid;
-				split_info.host_lpcr = vc->kvm->arch.host_lpcr;
-				split_info.do_set = 1;
-			}
 		}
 
 		/* order writes to split_info before kvm_split_mode pointer */
@@ -3281,7 +3268,6 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
 	for (thr = 0; thr < controlled_threads; ++thr) {
 		struct paca_struct *paca = paca_ptrs[pcpu + thr];
 
-		paca->kvm_hstate.tid = thr;
 		paca->kvm_hstate.napping = 0;
 		paca->kvm_hstate.kvm_split_mode = sip;
 	}
@@ -3355,10 +3341,8 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
 	 * When doing micro-threading, poke the inactive threads as well.
 	 * This gets them to the nap instruction after kvm_do_nap,
 	 * which reduces the time taken to unsplit later.
-	 * For POWER9 HPT guest on radix host, we need all the secondary
-	 * threads woken up so they can do the LPCR/LPIDR change.
 	 */
-	if (cmd_bit || hpt_on_radix) {
+	if (cmd_bit) {
 		split_info.do_nap = 1;	/* ask secondaries to nap when done */
 		for (thr = 1; thr < threads_per_subcore; ++thr)
 			if (!(active & (1 << thr)))
@@ -3419,19 +3403,8 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
 			cpu_relax();
 			++loops;
 		}
-	} else if (hpt_on_radix) {
-		/* Wait for all threads to have seen final sync */
-		for (thr = 1; thr < controlled_threads; ++thr) {
-			struct paca_struct *paca = paca_ptrs[pcpu + thr];
-
-			while (paca->kvm_hstate.kvm_split_mode) {
-				HMT_low();
-				barrier();
-			}
-			HMT_medium();
-		}
+		split_info.do_nap = 0;
 	}
-	split_info.do_nap = 0;
 
 	kvmppc_set_host_core(pcpu);
 
@@ -4216,7 +4189,6 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
 
 	kvmppc_clear_host_core(pcpu);
 
-	local_paca->kvm_hstate.tid = 0;
 	local_paca->kvm_hstate.napping = 0;
 	local_paca->kvm_hstate.kvm_split_mode = NULL;
 	kvmppc_start_thread(vcpu, vc);
@@ -4401,15 +4373,11 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu)
 
 	do {
 		/*
-		 * The early POWER9 chips that can't mix radix and HPT threads
-		 * on the same core also need the workaround for the problem
-		 * where the TLB would prefetch entries in the guest exit path
-		 * for radix guests using the guest PIDR value and LPID 0.
-		 * The workaround is in the old path (kvmppc_run_vcpu())
-		 * but not the new path (kvmhv_run_single_vcpu()).
+		 * The TLB prefetch bug fixup is only in the kvmppc_run_vcpu
+		 * path, which also handles hash and dependent threads mode.
 		 */
 		if (kvm->arch.threads_indep && kvm_is_radix(kvm) &&
-		    !no_mixing_hpt_and_radix)
+		    !cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG))
 			r = kvmhv_run_single_vcpu(vcpu, ~(u64)0,
 						  vcpu->arch.vcore->lpcr);
 		else