KVM: PPC: e500mc: Add support for single threaded vcpus on e6500 core

ePAPR represents hardware threads as cpu node properties in device tree.
So with existing QEMU, hardware threads are simply exposed as vcpus with
one hardware thread.

The e6500 core shares TLBs between hardware threads. Without tlb write
conditional instruction, the Linux kernel uses per core mechanisms to
protect against duplicate TLB entries.

The guest is unable to detect real siblings threads, so it can't use the
TLB protection mechanism. An alternative solution is to use the hypervisor
to allocate different lpids to guest's vcpus that runs simultaneous on real
siblings threads. On systems with two threads per core this patch halves
the size of the lpid pool that the allocator sees and use two lpids per VM.
Use even numbers to speedup vcpu lpid computation with consecutive lpids
per VM: vm1 will use lpids 2 and 3, vm2 lpids 4 and 5, and so on.

Signed-off-by: Mihai Caraman <[e-mail]>
[agraf: fix spelling]
Signed-off-by: Alexander Graf <[e-mail]>

arch/powerpc/include/asm/kvm_booke.h

···
 #include <linux/types.h>
 #include <linux/kvm_host.h>
 
-/* LPIDs we support with this build -- runtime limit may be lower */
+/*
+ * Number of available lpids. Only the low-order 6 bits of LPID rgister are
+ * implemented on e500mc+ cores.
+ */
 #define KVMPPC_NR_LPIDS                        64
 
 #define KVMPPC_INST_EHPRIV		0x7c00021c

arch/powerpc/kvm/e500.h

···
 #include <linux/kvm_host.h>
 #include <asm/mmu-book3e.h>
 #include <asm/tlb.h>
+#include <asm/cputhreads.h>
 
 enum vcpu_ftr {
 	VCPU_FTR_MMU_V2
···
 #define kvmppc_e500_get_tlb_stid(vcpu, gtlbe)       get_tlb_tid(gtlbe)
 #define get_tlbmiss_tid(vcpu)           get_cur_pid(vcpu)
 #define get_tlb_sts(gtlbe)              (gtlbe->mas1 & MAS1_TS)
+
+/*
+ * These functions should be called with preemption disabled
+ * and the returned value is valid only in that context
+ */
+static inline int get_thread_specific_lpid(int vm_lpid)
+{
+	int vcpu_lpid = vm_lpid;
+
+	if (threads_per_core == 2)
+		vcpu_lpid |= smp_processor_id() & 1;
+
+	return vcpu_lpid;
+}
+
+static inline int get_lpid(struct kvm_vcpu *vcpu)
+{
+	return get_thread_specific_lpid(vcpu->kvm->arch.lpid);
+}
 #else
 unsigned int kvmppc_e500_get_tlb_stid(struct kvm_vcpu *vcpu,
 				      struct kvm_book3e_206_tlb_entry *gtlbe);

arch/powerpc/kvm/e500_mmu_host.c

···
  * writing shadow tlb entry to host TLB
  */
 static inline void __write_host_tlbe(struct kvm_book3e_206_tlb_entry *stlbe,
-				     uint32_t mas0)
+				     uint32_t mas0,
+				     uint32_t lpid)
 {
 	unsigned long flags;
 
···
 	mtspr(SPRN_MAS3, (u32)stlbe->mas7_3);
 	mtspr(SPRN_MAS7, (u32)(stlbe->mas7_3 >> 32));
 #ifdef CONFIG_KVM_BOOKE_HV
-	mtspr(SPRN_MAS8, stlbe->mas8);
+	mtspr(SPRN_MAS8, MAS8_TGS | get_thread_specific_lpid(lpid));
 #endif
 	asm volatile("isync; tlbwe" : : : "memory");
 
···
 
 	if (tlbsel == 0) {
 		mas0 = get_host_mas0(stlbe->mas2);
-		__write_host_tlbe(stlbe, mas0);
+		__write_host_tlbe(stlbe, mas0, vcpu_e500->vcpu.kvm->arch.lpid);
 	} else {
 		__write_host_tlbe(stlbe,
 				  MAS0_TLBSEL(1) |
-				  MAS0_ESEL(to_htlb1_esel(sesel)));
+				  MAS0_ESEL(to_htlb1_esel(sesel)),
+				  vcpu_e500->vcpu.kvm->arch.lpid);
 	}
 }
 
···
 		       MAS3_SW | MAS3_SR | MAS3_UW | MAS3_UR;
 	magic.mas8 = 0;
 
-	__write_host_tlbe(&magic, MAS0_TLBSEL(1) | MAS0_ESEL(tlbcam_index));
+	__write_host_tlbe(&magic, MAS0_TLBSEL(1) | MAS0_ESEL(tlbcam_index), 0);
 	preempt_enable();
 }
 #endif
···
 	stlbe->mas2 = (gvaddr & MAS2_EPN) | (ref->flags & E500_TLB_MAS2_ATTR);
 	stlbe->mas7_3 = ((u64)pfn << PAGE_SHIFT) |
 			e500_shadow_mas3_attrib(gtlbe->mas7_3, pr);
-
-#ifdef CONFIG_KVM_BOOKE_HV
-	stlbe->mas8 = MAS8_TGS | vcpu->kvm->arch.lpid;
-#endif
 }
 
 static inline int kvmppc_e500_shadow_map(struct kvmppc_vcpu_e500 *vcpu_e500,
···
 
 	local_irq_save(flags);
 	mtspr(SPRN_MAS6, (vcpu->arch.pid << MAS6_SPID_SHIFT) | addr_space);
-	mtspr(SPRN_MAS5, MAS5_SGS | vcpu->kvm->arch.lpid);
+	mtspr(SPRN_MAS5, MAS5_SGS | get_lpid(vcpu));
 	asm volatile("tlbsx 0, %[geaddr]\n" : :
 		     [geaddr] "r" (geaddr));
 	mtspr(SPRN_MAS5, 0);

arch/powerpc/kvm/e500mc.c

···
 		return;
 	}
 
-
-	tag = PPC_DBELL_LPID(vcpu->kvm->arch.lpid) | vcpu->vcpu_id;
+	preempt_disable();
+	tag = PPC_DBELL_LPID(get_lpid(vcpu)) | vcpu->vcpu_id;
 	mb();
 	ppc_msgsnd(dbell_type, 0, tag);
+	preempt_enable();
 }
 
 /* gtlbe must not be mapped by more than one host tlb entry */
···
 {
 	unsigned int tid, ts;
 	gva_t eaddr;
-	u32 val, lpid;
+	u32 val;
 	unsigned long flags;
 
 	ts = get_tlb_ts(gtlbe);
 	tid = get_tlb_tid(gtlbe);
-	lpid = vcpu_e500->vcpu.kvm->arch.lpid;
 
 	/* We search the host TLB to invalidate its shadow TLB entry */
 	val = (tid << 16) | ts;
···
 	local_irq_save(flags);
 
 	mtspr(SPRN_MAS6, val);
-	mtspr(SPRN_MAS5, MAS5_SGS | lpid);
+	mtspr(SPRN_MAS5, MAS5_SGS | get_lpid(&vcpu_e500->vcpu));
 
 	asm volatile("tlbsx 0, %[eaddr]\n" : : [eaddr] "r" (eaddr));
 	val = mfspr(SPRN_MAS1);
···
 	unsigned long flags;
 
 	local_irq_save(flags);
-	mtspr(SPRN_MAS5, MAS5_SGS | vcpu_e500->vcpu.kvm->arch.lpid);
+	mtspr(SPRN_MAS5, MAS5_SGS | get_lpid(&vcpu_e500->vcpu));
 	asm volatile("tlbilxlpid");
 	mtspr(SPRN_MAS5, 0);
 	local_irq_restore(flags);
···
 {
 }
 
+/* We use two lpids per VM */
 static DEFINE_PER_CPU(struct kvm_vcpu *[KVMPPC_NR_LPIDS], last_vcpu_of_lpid);
 
 static void kvmppc_core_vcpu_load_e500mc(struct kvm_vcpu *vcpu, int cpu)
···
 
 	kvmppc_booke_vcpu_load(vcpu, cpu);
 
-	mtspr(SPRN_LPID, vcpu->kvm->arch.lpid);
+	mtspr(SPRN_LPID, get_lpid(vcpu));
 	mtspr(SPRN_EPCR, vcpu->arch.shadow_epcr);
 	mtspr(SPRN_GPIR, vcpu->vcpu_id);
 	mtspr(SPRN_MSRP, vcpu->arch.shadow_msrp);
+	vcpu->arch.eplc = EPC_EGS | (get_lpid(vcpu) << EPC_ELPID_SHIFT);
+	vcpu->arch.epsc = vcpu->arch.eplc;
 	mtspr(SPRN_EPLC, vcpu->arch.eplc);
 	mtspr(SPRN_EPSC, vcpu->arch.epsc);
 
···
 	mtspr(SPRN_GESR, vcpu->arch.shared->esr);
 
 	if (vcpu->arch.oldpir != mfspr(SPRN_PIR) ||
-	    __get_cpu_var(last_vcpu_of_lpid)[vcpu->kvm->arch.lpid] != vcpu) {
+	    __get_cpu_var(last_vcpu_of_lpid)[get_lpid(vcpu)] != vcpu) {
 		kvmppc_e500_tlbil_all(vcpu_e500);
-		__get_cpu_var(last_vcpu_of_lpid)[vcpu->kvm->arch.lpid] = vcpu;
+		__get_cpu_var(last_vcpu_of_lpid)[get_lpid(vcpu)] = vcpu;
 	}
 }
 
···
 	vcpu->arch.shadow_epcr |= SPRN_EPCR_ICM;
 #endif
 	vcpu->arch.shadow_msrp = MSRP_UCLEP | MSRP_PMMP;
-	vcpu->arch.eplc = EPC_EGS | (vcpu->kvm->arch.lpid << EPC_ELPID_SHIFT);
-	vcpu->arch.epsc = vcpu->arch.eplc;
 
 	vcpu->arch.pvr = mfspr(SPRN_PVR);
 	vcpu_e500->svr = mfspr(SPRN_SVR);
···
 	if (lpid < 0)
 		return lpid;
 
+	/*
+	 * Use two lpids per VM on cores with two threads like e6500. Use
+	 * even numbers to speedup vcpu lpid computation with consecutive lpids
+	 * per VM. vm1 will use lpids 2 and 3, vm2 lpids 4 and 5, and so on.
+	 */
+	if (threads_per_core == 2)
+		lpid <<= 1;
+
 	kvm->arch.lpid = lpid;
 	return 0;
 }
 
 static void kvmppc_core_destroy_vm_e500mc(struct kvm *kvm)
 {
-	kvmppc_free_lpid(kvm->arch.lpid);
+	int lpid = kvm->arch.lpid;
+
+	if (threads_per_core == 2)
+		lpid >>= 1;
+
+	kvmppc_free_lpid(lpid);
 }
 
 static struct kvmppc_ops kvm_ops_e500mc = {
···
 	if (r)
 		goto err_out;
 
-	kvmppc_init_lpid(64);
+	/*
+	 * Use two lpids per VM on dual threaded processors like e6500
+	 * to workarround the lack of tlb write conditional instruction.
+	 * Expose half the number of available hardware lpids to the lpid
+	 * allocator.
+	 */
+	kvmppc_init_lpid(KVMPPC_NR_LPIDS/threads_per_core);
 	kvmppc_claim_lpid(0); /* host */
 
 	r = kvm_init(NULL, sizeof(struct kvmppc_vcpu_e500), 0, THIS_MODULE);