KVM: PPC: Book3S HV: Add a per vcpu cache for recently page faulted MMIO entries

This keeps a per vcpu cache for recently page faulted MMIO entries.
On a page fault, if the entry exists in the cache, we can avoid some
time-consuming paths, for example, looking up HPT, locking HPTE twice
and searching mmio gfn from memslots, then directly call
kvmppc_hv_emulate_mmio().

In current implenment, we limit the size of cache to four. We think
it's enough to cover the high-frequency MMIO HPTEs in most case.
For example, considering the case of using virtio device, for virtio
legacy devices, one HPTE could handle notifications from up to
1024 (64K page / 64 byte Port IO register) devices, so one cache entry
is enough; for virtio modern devices, we always need one HPTE to handle
notification for each device because modern device would use a 8M MMIO
register to notify host instead of Port IO register, typically the
system's configuration should not exceed four virtio devices per
vcpu, four cache entry is also enough in this case. Of course, if needed,
we could also modify the macro to a module parameter in the future.

Signed-off-by: Yongji Xie <xyjxie@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 28350a294b1e..20ef27d09d05 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -246,6 +246,7 @@ struct kvm_arch {
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 	unsigned long hpt_virt;
 	struct revmap_entry *revmap;
+	atomic64_t mmio_update;
 	unsigned int host_lpid;
 	unsigned long host_lpcr;
 	unsigned long sdr1;
@@ -408,6 +409,24 @@ struct kvmppc_passthru_irqmap {
 #define KVMPPC_IRQ_MPIC		1
 #define KVMPPC_IRQ_XICS		2
 
+#define MMIO_HPTE_CACHE_SIZE	4
+
+struct mmio_hpte_cache_entry {
+	unsigned long hpte_v;
+	unsigned long hpte_r;
+	unsigned long rpte;
+	unsigned long pte_index;
+	unsigned long eaddr;
+	unsigned long slb_v;
+	long mmio_update;
+	unsigned int slb_base_pshift;
+};
+
+struct mmio_hpte_cache {
+	struct mmio_hpte_cache_entry entry[MMIO_HPTE_CACHE_SIZE];
+	unsigned int index;
+};
+
 struct openpic;
 
 struct kvm_vcpu_arch {
@@ -655,9 +674,11 @@ struct kvm_vcpu_arch {
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 	struct kvm_vcpu_arch_shared shregs;
 
+	struct mmio_hpte_cache mmio_cache;
 	unsigned long pgfault_addr;
 	long pgfault_index;
 	unsigned long pgfault_hpte[2];
+	struct mmio_hpte_cache_entry *pgfault_cache;
 
 	struct task_struct *run_task;
 	struct kvm_run *kvm_run;