KVM: PPC: Allow book3s_hv guests to use SMT processor modes

This lifts the restriction that book3s_hv guests can only run one
hardware thread per core, and allows them to use up to 4 threads
per core on POWER7.  The host still has to run single-threaded.

This capability is advertised to qemu through a new KVM_CAP_PPC_SMT
capability.  The return value of the ioctl querying this capability
is the number of vcpus per virtual CPU core (vcore), currently 4.

To use this, the host kernel should be booted with all threads
active, and then all the secondary threads should be offlined.
This will put the secondary threads into nap mode.  KVM will then
wake them from nap mode and use them for running guest code (while
they are still offline).  To wake the secondary threads, we send
them an IPI using a new xics_wake_cpu() function, implemented in
arch/powerpc/sysdev/xics/icp-native.c.  In other words, at this stage
we assume that the platform has a XICS interrupt controller and
we are using icp-native.c to drive it.  Since the woken thread will
need to acknowledge and clear the IPI, we also export the base
physical address of the XICS registers using kvmppc_set_xics_phys()
for use in the low-level KVM book3s code.

When a vcpu is created, it is assigned to a virtual CPU core.
The vcore number is obtained by dividing the vcpu number by the
number of threads per core in the host.  This number is exported
to userspace via the KVM_CAP_PPC_SMT capability.  If qemu wishes
to run the guest in single-threaded mode, it should make all vcpu
numbers be multiples of the number of threads per core.

We distinguish three states of a vcpu: runnable (i.e., ready to execute
the guest), blocked (that is, idle), and busy in host.  We currently
implement a policy that the vcore can run only when all its threads
are runnable or blocked.  This way, if a vcpu needs to execute elsewhere
in the kernel or in qemu, it can do so without being starved of CPU
by the other vcpus.

When a vcore starts to run, it executes in the context of one of the
vcpu threads.  The other vcpu threads all go to sleep and stay asleep
until something happens requiring the vcpu thread to return to qemu,
or to wake up to run the vcore (this can happen when another vcpu
thread goes from busy in host state to blocked).

It can happen that a vcpu goes from blocked to runnable state (e.g.
because of an interrupt), and the vcore it belongs to is already
running.  In that case it can start to run immediately as long as
the none of the vcpus in the vcore have started to exit the guest.
We send the next free thread in the vcore an IPI to get it to start
to execute the guest.  It synchronizes with the other threads via
the vcore->entry_exit_count field to make sure that it doesn't go
into the guest if the other vcpus are exiting by the time that it
is ready to actually enter the guest.

Note that there is no fixed relationship between the hardware thread
number and the vcpu number.  Hardware threads are assigned to vcpus
as they become runnable, so we will always use the lower-numbered
hardware threads in preference to higher-numbered threads if not all
the vcpus in the vcore are runnable, regardless of which vcpus are
runnable.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

1 files changed, 45 insertions, 1 deletions

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 5616e39a7fa..0d6d569e19c 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -25,10 +25,14 @@
 #include <linux/interrupt.h>
 #include <linux/types.h>
 #include <linux/kvm_types.h>
+#include <linux/threads.h>
+#include <linux/spinlock.h>
 #include <linux/kvm_para.h>
 #include <asm/kvm_asm.h>
+#include <asm/processor.h>
 
-#define KVM_MAX_VCPUS 1
+#define KVM_MAX_VCPUS		NR_CPUS
+#define KVM_MAX_VCORES		NR_CPUS
 #define KVM_MEMORY_SLOTS 32
 /* memory slots that does not exposed to userspace */
 #define KVM_PRIVATE_MEM_SLOTS 4
@@ -167,9 +171,34 @@ struct kvm_arch {
 	int tlbie_lock;
 	struct list_head spapr_tce_tables;
 	unsigned short last_vcpu[NR_CPUS];
+	struct kvmppc_vcore *vcores[KVM_MAX_VCORES];
 #endif /* CONFIG_KVM_BOOK3S_64_HV */
 };
 
+/*
+ * Struct for a virtual core.
+ * Note: entry_exit_count combines an entry count in the bottom 8 bits
+ * and an exit count in the next 8 bits.  This is so that we can
+ * atomically increment the entry count iff the exit count is 0
+ * without taking the lock.
+ */
+struct kvmppc_vcore {
+	int n_runnable;
+	int n_blocked;
+	int num_threads;
+	int entry_exit_count;
+	int n_woken;
+	int nap_count;
+	u16 pcpu;
+	u8 vcore_running;
+	u8 in_guest;
+	struct list_head runnable_threads;
+	spinlock_t lock;
+};
+
+#define VCORE_ENTRY_COUNT(vc)	((vc)->entry_exit_count & 0xff)
+#define VCORE_EXIT_COUNT(vc)	((vc)->entry_exit_count >> 8)
+
 struct kvmppc_pte {
 	ulong eaddr;
 	u64 vpage;
@@ -365,14 +394,29 @@ struct kvm_vcpu_arch {
 	struct slb_shadow *slb_shadow;
 	struct dtl *dtl;
 	struct dtl *dtl_end;
+
+	struct kvmppc_vcore *vcore;
+	int ret;
 	int trap;
+	int state;
+	int ptid;
+	wait_queue_head_t cpu_run;
+
 	struct kvm_vcpu_arch_shared *shared;
 	unsigned long magic_page_pa; /* phys addr to map the magic page to */
 	unsigned long magic_page_ea; /* effect. addr to map the magic page to */
 
 #ifdef CONFIG_KVM_BOOK3S_64_HV
 	struct kvm_vcpu_arch_shared shregs;
+
+	struct list_head run_list;
+	struct task_struct *run_task;
+	struct kvm_run *kvm_run;
 #endif
 };
 
+#define KVMPPC_VCPU_BUSY_IN_HOST	0
+#define KVMPPC_VCPU_BLOCKED		1
+#define KVMPPC_VCPU_RUNNABLE		2
+
 #endif /* __POWERPC_KVM_HOST_H__ */