KVM guests have certain restrictions and performance quirks when
using doorbells. This patch tests for KVM environment in doorbell
setup, and optimises IPI performance:
- PowerVM guests may now use doorbells even if they are secure.
- KVM guests no longer use doorbells if XIVE is available.
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
---
arch/powerpc/include/asm/firmware.h | 2 ++
arch/powerpc/include/asm/kvm_para.h | 26 ++--------------
arch/powerpc/platforms/pseries/firmware.c | 14 +++++++++
arch/powerpc/platforms/pseries/smp.c | 38 ++++++++++++++---------
4 files changed, 42 insertions(+), 38 deletions(-)
diff --git a/arch/powerpc/include/asm/firmware.h b/arch/powerpc/include/asm/firmware.h
index 6003c2e533a0..4dadb84ff2b2 100644
--- a/arch/powerpc/include/asm/firmware.h
+++ b/arch/powerpc/include/asm/firmware.h
@@ -134,7 +134,9 @@ extern unsigned int __start___fw_ftr_fixup, __stop___fw_ftr_fixup;
#ifdef CONFIG_PPC_PSERIES
void pseries_probe_fw_features(void);
+bool is_kvm_guest(void);
#else
+static inline bool is_kvm_guest(void) { return false; }
static inline void pseries_probe_fw_features(void) { };
#endif
diff --git a/arch/powerpc/include/asm/kvm_para.h b/arch/powerpc/include/asm/kvm_para.h
index 9c1f6b4b9bbf..744612054c94 100644
--- a/arch/powerpc/include/asm/kvm_para.h
+++ b/arch/powerpc/include/asm/kvm_para.h
@@ -8,35 +8,15 @@
#ifndef __POWERPC_KVM_PARA_H__
#define __POWERPC_KVM_PARA_H__
-#include <uapi/asm/kvm_para.h>
-
-#ifdef CONFIG_KVM_GUEST
-
-#include <linux/of.h>
-
-static inline int kvm_para_available(void)
-{
- struct device_node *hyper_node;
-
- hyper_node = of_find_node_by_path("/hypervisor");
- if (!hyper_node)
- return 0;
+#include <asm/firmware.h>
- if (!of_device_is_compatible(hyper_node, "linux,kvm"))
- return 0;
-
- return 1;
-}
-
-#else
+#include <uapi/asm/kvm_para.h>
static inline int kvm_para_available(void)
{
- return 0;
+ return IS_ENABLED(CONFIG_KVM_GUEST) && is_kvm_guest();
}
-#endif
-
static inline unsigned int kvm_arch_para_features(void)
{
unsigned long r;
diff --git a/arch/powerpc/platforms/pseries/firmware.c b/arch/powerpc/platforms/pseries/firmware.c
index 3e49cc23a97a..f58eb10011dd 100644
--- a/arch/powerpc/platforms/pseries/firmware.c
+++ b/arch/powerpc/platforms/pseries/firmware.c
@@ -184,3 +184,17 @@ void __init pseries_probe_fw_features(void)
{
of_scan_flat_dt(probe_fw_features, NULL);
}
+
+bool is_kvm_guest(void)
+{
+ struct device_node *hyper_node;
+
+ hyper_node = of_find_node_by_path("/hypervisor");
+ if (!hyper_node)
+ return 0;
+
+ if (!of_device_is_compatible(hyper_node, "linux,kvm"))
+ return 0;
+
+ return 1;
+}
diff --git a/arch/powerpc/platforms/pseries/smp.c b/arch/powerpc/platforms/pseries/smp.c
index 67e6ad5076ce..7af0003b40b6 100644
--- a/arch/powerpc/platforms/pseries/smp.c
+++ b/arch/powerpc/platforms/pseries/smp.c
@@ -236,24 +236,32 @@ static __init void pSeries_smp_probe(void)
if (!cpu_has_feature(CPU_FTR_SMT))
return;
- /*
- * KVM emulates doorbells by disabling FSCR[MSGP] so msgsndp faults
- * to the hypervisor which then reads the instruction from guest
- * memory. This can't be done if the guest is secure, so don't use
- * doorbells in secure guests.
- *
- * Under PowerVM, FSCR[MSGP] is enabled so doorbells could be used
- * by secure guests if we distinguished this from KVM.
- */
- if (is_secure_guest())
- return;
+ if (is_kvm_guest()) {
+ /*
+ * KVM emulates doorbells by disabling FSCR[MSGP] so msgsndp
+ * faults to the hypervisor which then reads the instruction
+ * from guest memory, which tends to be slower than using XIVE.
+ */
+ if (xive_enabled())
+ return;
+
+ /*
+ * XICS hcalls aren't as fast, so we can use msgsndp (which
+ * also helps exercise KVM emulation), however KVM can't
+ * emulate secure guests because it can't read the instruction
+ * out of their memory.
+ */
+ if (is_secure_guest())
+ return;
+ }
/*
- * The guest can use doobells for SMT sibling IPIs, which stay in
- * the core rather than going to the interrupt controller. This
- * tends to be slower under KVM where doorbells are emulated, but
- * faster for PowerVM where they're enabled.
+ * Under PowerVM, FSCR[MSGP] is enabled as guest vCPU siblings are
+ * gang scheduled on the same physical core, so doorbells are always
+ * faster than the interrupt controller, and they can be used by
+ * secure guests.
*/
+
ic_cause_ipi = smp_ops->cause_ipi;
smp_ops->cause_ipi = dbell_or_ic_cause_ipi;
}
--
2.23.0
