powerpc/dexcr: Add initial Dynamic Execution Control Register (DEXCR) support

ISA 3.1B introduces the Dynamic Execution Control Register (DEXCR). It
is a per-cpu register that allows control over various CPU behaviours
including branch hint usage, indirect branch speculation, and
hashst/hashchk support.

Add some definitions and basic support for the DEXCR in the kernel.
Right now it just

  * Initialises the DEXCR and HASHKEYR to a fixed value when a CPU
    onlines.
  * Clears them in reset_sprs().
  * Detects when the NPHIE aspect is supported (the others don't get
    looked at in this series, so there's no need to waste a CPU_FTR
    on them).

We initialise the HASHKEYR to ensure that all cores have the same key,
so an HV enforced NPHIE + swapping cores doesn't randomly crash a
process using hash instructions. The stores to HASHKEYR are
unconditional because the ISA makes no mention of the SPR being missing
if support for doing the hashes isn't present. So all that would happen
is the HASHKEYR value gets ignored. This helps slightly if NPHIE
detection fails; e.g., we currently only detect it on pseries.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
[mpe: Use simple values for DEXCR constants]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230616034846.311705-4-bgray@linux.ibm.com

arch/powerpc/include/asm/book3s/64/kexec.h

@@ -21,6 +21,11 @@ static inline void reset_sprs(void)
 			plpar_set_ciabr(0);
 	}
 
+	if (cpu_has_feature(CPU_FTR_ARCH_31)) {
+		mtspr(SPRN_DEXCR, 0);
+		mtspr(SPRN_HASHKEYR, 0);
+	}
+
 	/*  Do we need isync()? We are going via a kexec reset */
 	isync();
 }

arch/powerpc/include/asm/cputable.h

@@ -192,6 +192,7 @@ static inline void cpu_feature_keys_init(void) { }
 #define CPU_FTR_P9_RADIX_PREFETCH_BUG	LONG_ASM_CONST(0x0002000000000000)
 #define CPU_FTR_ARCH_31			LONG_ASM_CONST(0x0004000000000000)
 #define CPU_FTR_DAWR1			LONG_ASM_CONST(0x0008000000000000)
+#define CPU_FTR_DEXCR_NPHIE		LONG_ASM_CONST(0x0010000000000000)
 
 #ifndef __ASSEMBLY__
 
@@ -451,7 +452,8 @@ static inline void cpu_feature_keys_init(void) { }
 	    CPU_FTR_CFAR | CPU_FTR_HVMODE | CPU_FTR_VMX_COPY | \
 	    CPU_FTR_DBELL | CPU_FTR_HAS_PPR | CPU_FTR_ARCH_207S | \
 	    CPU_FTR_ARCH_300 | CPU_FTR_ARCH_31 | \
-	    CPU_FTR_DAWR | CPU_FTR_DAWR1)
+	    CPU_FTR_DAWR | CPU_FTR_DAWR1 | \
+	    CPU_FTR_DEXCR_NPHIE)
 #define CPU_FTRS_CELL	(CPU_FTR_LWSYNC | \
 	    CPU_FTR_PPCAS_ARCH_V2 | CPU_FTR_CTRL | \
 	    CPU_FTR_ALTIVEC_COMP | CPU_FTR_MMCRA | CPU_FTR_SMT | \

arch/powerpc/include/asm/reg.h

@@ -382,7 +382,17 @@
 #define SPRN_HIOR	0x137	/* 970 Hypervisor interrupt offset */
 #define SPRN_RMOR	0x138	/* Real mode offset register */
 #define SPRN_HRMOR	0x139	/* Real mode offset register */
+#define SPRN_HDEXCR_RO	0x1C7	/* Hypervisor DEXCR (non-privileged, readonly) */
+#define SPRN_HASHKEYR	0x1D4	/* Non-privileged hashst/hashchk key register */
+#define SPRN_HDEXCR	0x1D7	/* Hypervisor dynamic execution control register */
+#define SPRN_DEXCR_RO	0x32C	/* DEXCR (non-privileged, readonly) */
 #define SPRN_ASDR	0x330	/* Access segment descriptor register */
+#define SPRN_DEXCR	0x33C	/* Dynamic execution control register */
+#define   DEXCR_PR_SBHE	  0x80000000UL /* 0: Speculative Branch Hint Enable */
+#define   DEXCR_PR_IBRTPD 0x10000000UL /* 3: Indirect Branch Recurrent Target Prediction Disable */
+#define   DEXCR_PR_SRAPD  0x08000000UL /* 4: Subroutine Return Address Prediction Disable */
+#define   DEXCR_PR_NPHIE  0x04000000UL /* 5: Non-Privileged Hash Instruction Enable */
+#define   DEXCR_INIT	DEXCR_PR_NPHIE	/* Fixed DEXCR value to initialise all CPUs with */
 #define SPRN_IC		0x350	/* Virtual Instruction Count */
 #define SPRN_VTB	0x351	/* Virtual Time Base */
 #define SPRN_LDBAR	0x352	/* LD Base Address Register */

arch/powerpc/kernel/cpu_setup_power.c

@@ -126,6 +126,12 @@ static void init_PMU_ISA31(void)
 	mtspr(SPRN_MMCR0, MMCR0_FC | MMCR0_PMCCEXT);
 }
 
+static void init_DEXCR(void)
+{
+	mtspr(SPRN_DEXCR, DEXCR_INIT);
+	mtspr(SPRN_HASHKEYR, 0);
+}
+
 /*
  * Note that we can be called twice of pseudo-PVRs.
  * The parameter offset is not used.
@@ -241,6 +247,7 @@ void __setup_cpu_power10(unsigned long offset, struct cpu_spec *t)
 	init_FSCR_power10();
 	init_PMU();
 	init_PMU_ISA31();
+	init_DEXCR();
 
 	if (!init_hvmode_206(t))
 		return;
@@ -263,6 +270,7 @@ void __restore_cpu_power10(void)
 	init_FSCR_power10();
 	init_PMU();
 	init_PMU_ISA31();
+	init_DEXCR();
 
 	msr = mfmsr();
 	if (!(msr & MSR_HV))

arch/powerpc/kernel/prom.c

@@ -182,6 +182,7 @@ static struct ibm_feature ibm_pa_features[] __initdata = {
 	  .cpu_user_ftrs2 = PPC_FEATURE2_HTM_COMP | PPC_FEATURE2_HTM_NOSC_COMP },
 
 	{ .pabyte = 64, .pabit = 0, .cpu_features = CPU_FTR_DAWR1 },
+	{ .pabyte = 68, .pabit = 5, .cpu_features = CPU_FTR_DEXCR_NPHIE },
 };
 
 /*