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, 16 insertions, 0 deletions

diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index 33a7d1f9167b..564ae8aa1961 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -88,6 +88,8 @@ long kvmppc_alloc_hpt(struct kvm *kvm, u32 *htab_orderp)
 	/* 128 (2**7) bytes in each HPTEG */
 	kvm->arch.hpt_mask = (1ul << (order - 7)) - 1;
 
+	atomic64_set(&kvm->arch.mmio_update, 0);
+
 	/* Allocate reverse map array */
 	rev = vmalloc(sizeof(struct revmap_entry) * kvm->arch.hpt_npte);
 	if (!rev) {
@@ -451,6 +453,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	unsigned int writing, write_ok;
 	struct vm_area_struct *vma;
 	unsigned long rcbits;
+	long mmio_update;
 
 	/*
 	 * Real-mode code has already searched the HPT and found the
@@ -460,6 +463,19 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	 */
 	if (ea != vcpu->arch.pgfault_addr)
 		return RESUME_GUEST;
+
+	if (vcpu->arch.pgfault_cache) {
+		mmio_update = atomic64_read(&kvm->arch.mmio_update);
+		if (mmio_update == vcpu->arch.pgfault_cache->mmio_update) {
+			r = vcpu->arch.pgfault_cache->rpte;
+			psize = hpte_page_size(vcpu->arch.pgfault_hpte[0], r);
+			gpa_base = r & HPTE_R_RPN & ~(psize - 1);
+			gfn_base = gpa_base >> PAGE_SHIFT;
+			gpa = gpa_base | (ea & (psize - 1));
+			return kvmppc_hv_emulate_mmio(run, vcpu, gpa, ea,
+						dsisr & DSISR_ISSTORE);
+		}
+	}
 	index = vcpu->arch.pgfault_index;
 	hptep = (__be64 *)(kvm->arch.hpt_virt + (index << 4));
 	rev = &kvm->arch.revmap[index];