KVM: PPC: Book3S HV: Update LPID allocator init for POWER9, Nested

The LPID allocator init is changed to:
- use mmu_lpid_bits rather than hard-coding;
- use KVM_MAX_NESTED_GUESTS for nested hypervisors;
- not reserve the top LPID on POWER9 and newer CPUs.

The reserved LPID is made a POWER7/8-specific detail.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220123120043.3586018-3-npiggin@gmail.com

arch/powerpc/include/asm/kvm_book3s_asm.h

@@ -15,7 +15,7 @@
 #define XICS_IPI		2	/* interrupt source # for IPIs */
 
 /* LPIDs we support with this build -- runtime limit may be lower */
-#define KVMPPC_NR_LPIDS			(LPID_RSVD + 1)
+#define KVMPPC_NR_LPIDS			(1UL << 12)
 
 /* Maximum number of threads per physical core */
 #define MAX_SMT_THREADS		8

arch/powerpc/include/asm/reg.h

@@ -473,8 +473,6 @@
 #ifndef SPRN_LPID
 #define SPRN_LPID	0x13F	/* Logical Partition Identifier */
 #endif
-#define   LPID_RSVD_POWER7	0x3ff	/* Reserved LPID for partn switching */
-#define   LPID_RSVD		0xfff	/* Reserved LPID for partn switching */
 #define	SPRN_HMER	0x150	/* Hypervisor maintenance exception reg */
 #define   HMER_DEBUG_TRIG	(1ul << (63 - 17)) /* Debug trigger */
 #define	SPRN_HMEER	0x151	/* Hyp maintenance exception enable reg */

arch/powerpc/kvm/book3s_64_mmu_hv.c

@@ -256,7 +256,7 @@ void kvmppc_map_vrma(struct kvm_vcpu *vcpu, struct kvm_memory_slot *memslot,
 
 int kvmppc_mmu_hv_init(void)
 {
-	unsigned long rsvd_lpid;
+	unsigned long nr_lpids;
 
 	if (!mmu_has_feature(MMU_FTR_LOCKLESS_TLBIE))
 		return -EINVAL;
@@ -264,16 +264,29 @@ int kvmppc_mmu_hv_init(void)
 	if (cpu_has_feature(CPU_FTR_HVMODE)) {
 		if (WARN_ON(mfspr(SPRN_LPID) != 0))
 			return -EINVAL;
+		nr_lpids = 1UL << mmu_lpid_bits;
+	} else {
+		nr_lpids = KVM_MAX_NESTED_GUESTS;
 	}
 
-	/* POWER8 and above have 12-bit LPIDs (10-bit in POWER7) */
-	if (cpu_has_feature(CPU_FTR_ARCH_207S))
-		rsvd_lpid = LPID_RSVD;
-	else
-		rsvd_lpid = LPID_RSVD_POWER7;
+	if (nr_lpids > KVMPPC_NR_LPIDS)
+		nr_lpids = KVMPPC_NR_LPIDS;
+
+	if (!cpu_has_feature(CPU_FTR_ARCH_300)) {
+		/* POWER7 has 10-bit LPIDs, POWER8 has 12-bit LPIDs */
+		if (cpu_has_feature(CPU_FTR_ARCH_207S))
+			WARN_ON(nr_lpids != 1UL << 12);
+		else
+			WARN_ON(nr_lpids != 1UL << 10);
+
+		/*
+		 * Reserve the last implemented LPID use in partition
+		 * switching for POWER7 and POWER8.
+		 */
+		nr_lpids -= 1;
+	}
 
-	/* rsvd_lpid is reserved for use in partition switching */
-	kvmppc_init_lpid(rsvd_lpid);
+	kvmppc_init_lpid(nr_lpids);
 
 	return 0;
 }

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -50,6 +50,14 @@
 #define STACK_SLOT_UAMOR	(SFS-88)
 #define STACK_SLOT_FSCR		(SFS-96)
 
+/*
+ * Use the last LPID (all implemented LPID bits = 1) for partition switching.
+ * This is reserved in the LPID allocator. POWER7 only implements 0x3ff, but
+ * we write 0xfff into the LPID SPR anyway, which seems to work and just
+ * ignores the top bits.
+ */
+#define   LPID_RSVD		0xfff
+
 /*
  * Call kvmppc_hv_entry in real mode.
  * Must be called with interrupts hard-disabled.

arch/powerpc/mm/init_64.c

@@ -372,6 +372,9 @@ void register_page_bootmem_memmap(unsigned long section_nr,
 
 #ifdef CONFIG_PPC_BOOK3S_64
 unsigned int mmu_lpid_bits;
+#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
+EXPORT_SYMBOL_GPL(mmu_lpid_bits);
+#endif
 unsigned int mmu_pid_bits;
 
 static bool disable_radix = !IS_ENABLED(CONFIG_PPC_RADIX_MMU_DEFAULT);