powerpc/mm: Remove kvm radix prefetch workaround for Power9 DD2.2

Commit a25bd72b ("powerpc/mm/radix: Workaround prefetch issue with
KVM") introduced a number of workarounds as coming out of a guest with
the mmu enabled would make the cpu would start running in hypervisor
state with the PID value from the guest. The cpu will then start
prefetching for the hypervisor with that PID value.

In Power9 DD2.2 the cpu behaviour was modified to fix this. When
accessing Quadrant 0 in hypervisor mode with LPID != 0 prefetching will
not be performed. This means that we can get rid of the workarounds for
Power9 DD2.2 and later revisions. Add a new cpu feature
CPU_FTR_P9_RADIX_PREFETCH_BUG to indicate if the workarounds are needed.
Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Acked-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191206031722.25781-1-jniethe5@gmail.com

arch/powerpc/include/asm/cputable.h

@@ -212,6 +212,7 @@ static inline void cpu_feature_keys_init(void) { }
 #define CPU_FTR_P9_TLBIE_STQ_BUG	LONG_ASM_CONST(0x0000400000000000)
 #define CPU_FTR_P9_TIDR			LONG_ASM_CONST(0x0000800000000000)
 #define CPU_FTR_P9_TLBIE_ERAT_BUG	LONG_ASM_CONST(0x0001000000000000)
+#define CPU_FTR_P9_RADIX_PREFETCH_BUG	LONG_ASM_CONST(0x0002000000000000)
 
 #ifndef __ASSEMBLY__
 
@@ -459,8 +460,10 @@ static inline void cpu_feature_keys_init(void) { }
 	    CPU_FTR_DBELL | CPU_FTR_HAS_PPR | CPU_FTR_ARCH_207S | \
 	    CPU_FTR_TM_COMP | CPU_FTR_ARCH_300 | CPU_FTR_PKEY | \
 	    CPU_FTR_P9_TLBIE_STQ_BUG | CPU_FTR_P9_TLBIE_ERAT_BUG | CPU_FTR_P9_TIDR)
-#define CPU_FTRS_POWER9_DD2_0 CPU_FTRS_POWER9
-#define CPU_FTRS_POWER9_DD2_1 (CPU_FTRS_POWER9 | CPU_FTR_POWER9_DD2_1)
+#define CPU_FTRS_POWER9_DD2_0 (CPU_FTRS_POWER9 | CPU_FTR_P9_RADIX_PREFETCH_BUG)
+#define CPU_FTRS_POWER9_DD2_1 (CPU_FTRS_POWER9 | \
+			       CPU_FTR_P9_RADIX_PREFETCH_BUG | \
+			       CPU_FTR_POWER9_DD2_1)
 #define CPU_FTRS_POWER9_DD2_2 (CPU_FTRS_POWER9 | CPU_FTR_POWER9_DD2_1 | \
 			       CPU_FTR_P9_TM_HV_ASSIST | \
 			       CPU_FTR_P9_TM_XER_SO_BUG)

arch/powerpc/kernel/dt_cpu_ftrs.c

@@ -727,17 +727,20 @@ static __init void cpufeatures_cpu_quirks(void)
 	/*
 	 * Not all quirks can be derived from the cpufeatures device tree.
 	 */
-	if ((version & 0xffffefff) == 0x004e0200)
-		; /* DD2.0 has no feature flag */
-	else if ((version & 0xffffefff) == 0x004e0201)
+	if ((version & 0xffffefff) == 0x004e0200) {
+		/* DD2.0 has no feature flag */
+		cur_cpu_spec->cpu_features |= CPU_FTR_P9_RADIX_PREFETCH_BUG;
+	} else if ((version & 0xffffefff) == 0x004e0201) {
 		cur_cpu_spec->cpu_features |= CPU_FTR_POWER9_DD2_1;
-	else if ((version & 0xffffefff) == 0x004e0202) {
+		cur_cpu_spec->cpu_features |= CPU_FTR_P9_RADIX_PREFETCH_BUG;
+	} else if ((version & 0xffffefff) == 0x004e0202) {
 		cur_cpu_spec->cpu_features |= CPU_FTR_P9_TM_HV_ASSIST;
 		cur_cpu_spec->cpu_features |= CPU_FTR_P9_TM_XER_SO_BUG;
 		cur_cpu_spec->cpu_features |= CPU_FTR_POWER9_DD2_1;
-	} else if ((version & 0xffff0000) == 0x004e0000)
+	} else if ((version & 0xffff0000) == 0x004e0000) {
 		/* DD2.1 and up have DD2_1 */
 		cur_cpu_spec->cpu_features |= CPU_FTR_POWER9_DD2_1;
+	}
 
 	if ((version & 0xffff0000) == 0x004e0000) {
 		cur_cpu_spec->cpu_features &= ~(CPU_FTR_DAWR);

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -1801,6 +1801,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
 	tlbsync
 	ptesync
 
+BEGIN_FTR_SECTION
 	/* Radix: Handle the case where the guest used an illegal PID */
 	LOAD_REG_ADDR(r4, mmu_base_pid)
 	lwz	r3, VCPU_GUEST_PID(r9)
@@ -1830,6 +1831,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
 	addi	r7,r7,0x1000
 	bdnz	1b
 	ptesync
+END_FTR_SECTION_IFSET(CPU_FTR_P9_RADIX_PREFETCH_BUG)
 
 2:
 #endif /* CONFIG_PPC_RADIX_MMU */

arch/powerpc/mm/book3s64/radix_pgtable.c

@@ -337,7 +337,11 @@ static void __init radix_init_pgtable(void)
 	}
 
 	/* Find out how many PID bits are supported */
-	if (cpu_has_feature(CPU_FTR_HVMODE)) {
+	if (!cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG)) {
+		if (!mmu_pid_bits)
+			mmu_pid_bits = 20;
+		mmu_base_pid = 1;
+	} else if (cpu_has_feature(CPU_FTR_HVMODE)) {
 		if (!mmu_pid_bits)
 			mmu_pid_bits = 20;
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE

arch/powerpc/mm/book3s64/radix_tlb.c

@@ -1161,6 +1161,9 @@ extern void radix_kvm_prefetch_workaround(struct mm_struct *mm)
 	if (unlikely(pid == MMU_NO_CONTEXT))
 		return;
 
+	if (!cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG))
+		return;
+
 	/*
 	 * If this context hasn't run on that CPU before and KVM is
 	 * around, there's a slim chance that the guest on another