[Bionic][PATCH 1/1] KVM: PPC: Book3S HV: Allow HPT and radix on the same core for POWER9 v2.2

[Joseph Salisbury]

From: Paul Mackerras <paulus at ozlabs.org>

BugLink: http://bugs.launchpad.net/bugs/1756254

POWER9 chip versions starting with "Nimbus" v2.2 can support running
with some threads of a core in HPT mode and others in radix mode.
This means that we don't have to prohibit independent-threads mode
when running a HPT guest on a radix host, and we don't have to do any
of the synchronization between threads that was introduced in commit
c01015091a77 ("KVM: PPC: Book3S HV: Run HPT guests on POWER9 radix
hosts", 2017-10-19).

Rather than using up another CPU feature bit, we just do an
explicit test on the PVR (processor version register) at module
startup time to determine whether we have to take steps to avoid
having some threads in HPT mode and some in radix mode (so-called
"mixed mode").  We test for "Nimbus" (indicated by 0 or 1 in the top
nibble of the lower 16 bits) v2.2 or later, or "Cumulus" (indicated by
2 or 3 in that nibble) v1.1 or later.

Signed-off-by: Paul Mackerras <paulus at ozlabs.org>
(cherry picked from commit 00608e1f007e4cf6031485c5630e0e504bceef9b)
Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
---
 arch/powerpc/kvm/book3s_hv.c | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 6c402f6..d3a8b73 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -118,6 +118,9 @@ module_param_cb(h_ipi_redirect, &module_param_ops, &h_ipi_redirect,
 MODULE_PARM_DESC(h_ipi_redirect, "Redirect H_IPI wakeup to a free host core");
 #endif
 
+/* If set, the threads on each CPU core have to be in the same MMU mode */
+static bool no_mixing_hpt_and_radix;
+
 static void kvmppc_end_cede(struct kvm_vcpu *vcpu);
 static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu);
 
@@ -2385,8 +2388,8 @@ static void init_core_info(struct core_info *cip, struct kvmppc_vcore *vc)
 static bool subcore_config_ok(int n_subcores, int n_threads)
 {
 	/*
-	 * POWER9 "SMT4" cores are permanently in what is effectively a 4-way split-core
-	 * mode, with one thread per subcore.
+	 * POWER9 "SMT4" cores are permanently in what is effectively a 4-way
+	 * split-core mode, with one thread per subcore.
 	 */
 	if (cpu_has_feature(CPU_FTR_ARCH_300))
 		return n_subcores <= 4 && n_threads == 1;
@@ -2422,8 +2425,8 @@ 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) &&
+	/* 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;
 
@@ -2686,9 +2689,11 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
 	 * 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.
+	 * this is a HPT guest on a radix host machine where the
+	 * CPU threads may not be in different MMU modes.
 	 */
-	hpt_on_radix = radix_enabled() && !kvm_is_radix(vc->kvm);
+	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)) {
@@ -4456,6 +4461,19 @@ static int kvmppc_book3s_init_hv(void)
 
 	if (kvmppc_radix_possible())
 		r = kvmppc_radix_init();
+
+	/*
+	 * POWER9 chips before version 2.02 can't have some threads in
+	 * HPT mode and some in radix mode on the same core.
+	 */
+	if (cpu_has_feature(CPU_FTR_ARCH_300)) {
+		unsigned int pvr = mfspr(SPRN_PVR);
+		if ((pvr >> 16) == PVR_POWER9 &&
+		    (((pvr & 0xe000) == 0 && (pvr & 0xfff) < 0x202) ||
+		     ((pvr & 0xe000) == 0x2000 && (pvr & 0xfff) < 0x101)))
+			no_mixing_hpt_and_radix = true;
+	}
+
 	return r;
 }
 
-- 
2.7.4