KVM: PPC: Book3S HV: Run HPT guests on POWER9 radix hosts

This patch removes the restriction that a radix host can only run
radix guests, allowing us to run HPT (hashed page table) guests as
well.  This is useful because it provides a way to run old guest
kernels that know about POWER8 but not POWER9.

Unfortunately, POWER9 currently has a restriction that all threads
in a given code must either all be in HPT mode, or all in radix mode.
This means that when entering a HPT guest, we have to obtain control
of all 4 threads in the core and get them to switch their LPIDR and
LPCR registers, even if they are not going to run a guest.  On guest
exit we also have to get all threads to switch LPIDR and LPCR back
to host values.

To make this feasible, we require that KVM not be in the "independent
threads" mode, and that the CPU cores be in single-threaded mode from
the host kernel's perspective (only thread 0 online; threads 1, 2 and
3 offline).  That allows us to use the same code as on POWER8 for
obtaining control of the secondary threads.

To manage the LPCR/LPIDR changes required, we extend the kvm_split_info
struct to contain the information needed by the secondary threads.
All threads perform a barrier synchronization (where all threads wait
for every other thread to reach the synchronization point) on guest
entry, both before and after loading LPCR and LPIDR.  On guest exit,
they all once again perform a barrier synchronization both before
and after loading host values into LPCR and LPIDR.

Finally, it is also currently necessary to flush the entire TLB every
time we enter a HPT guest on a radix host.  We do this on thread 0
with a loop of tlbiel instructions.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

1 files changed, 38 insertions, 9 deletions

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index b5fbf7617952..fff62fdf1464 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -2414,6 +2414,11 @@ static bool can_dynamic_split(struct kvmppc_vcore *vc, struct core_info *cip)
 	if (!cpu_has_feature(CPU_FTR_ARCH_207S))
 		return false;
 
+	/* POWER9 currently requires all threads to be in the same MMU mode */
+	if (cpu_has_feature(CPU_FTR_ARCH_300) &&
+	    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))
@@ -2452,9 +2457,6 @@ 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 (kvm_is_radix(vc->kvm) != radix_enabled())
-			/* can't actually run HPT guest on radix host yet... */
-			vcpu->arch.ret = -EINVAL;
 		else if (vcpu->arch.vpa.update_pending ||
 			 vcpu->arch.slb_shadow.update_pending ||
 			 vcpu->arch.dtl.update_pending)
@@ -2643,6 +2645,7 @@ 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
@@ -2671,9 +2674,13 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
 	 * Make sure we are running on primary threads, and that secondary
 	 * threads are offline.  Also check if the number of threads in this
 	 * guest are greater than the current system threads per guest.
+	 * On POWER9, we need to be not in independent-threads mode if
+	 * this is a HPT guest on a radix host.
 	 */
-	if ((controlled_threads > 1) &&
-	    ((vc->num_threads > threads_per_subcore) || !on_primary_thread())) {
+	hpt_on_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)) {
 		for_each_runnable_thread(i, vcpu, vc) {
 			vcpu->arch.ret = -EBUSY;
 			kvmppc_remove_runnable(vc, vcpu);
@@ -2739,7 +2746,7 @@ 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) {
+	if (split > 1 || hpt_on_radix) {
 		sip = &split_info;
 		memset(&split_info, 0, sizeof(split_info));
 		for (sub = 0; sub < core_info.n_subcores; ++sub)
@@ -2761,13 +2768,24 @@ 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 */
 		smp_wmb();
 	}
-	for (thr = 0; thr < controlled_threads; ++thr)
+
+	for (thr = 0; thr < controlled_threads; ++thr) {
+		paca[pcpu + thr].kvm_hstate.tid = thr;
+		paca[pcpu + thr].kvm_hstate.napping = 0;
 		paca[pcpu + thr].kvm_hstate.kvm_split_mode = sip;
+	}
 
 	/* Initiate micro-threading (split-core) on POWER8 if required */
 	if (cmd_bit) {
@@ -2820,8 +2838,10 @@ 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) {
+	if (cmd_bit || hpt_on_radix) {
 		split_info.do_nap = 1;	/* ask secondaries to nap when done */
 		for (thr = 1; thr < threads_per_subcore; ++thr)
 			if (!(active & (1 << thr)))
@@ -2879,8 +2899,17 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
 			cpu_relax();
 			++loops;
 		}
-		split_info.do_nap = 0;
+	} else if (hpt_on_radix) {
+		/* Wait for all threads to have seen final sync */
+		for (thr = 1; thr < controlled_threads; ++thr) {
+			while (paca[pcpu + thr].kvm_hstate.kvm_split_mode) {
+				HMT_low();
+				barrier();
+			}
+			HMT_medium();
+		}
 	}
+	split_info.do_nap = 0;
 
 	kvmppc_set_host_core(pcpu);