riscv: add memory-type errata for T-Head

Some current cpus based on T-Head cores implement memory-types
way different than described in the svpbmt spec even going
so far as using PTE bits marked as reserved.

Add the T-Head vendor-id and necessary errata code to
replace the affected instructions.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Samuel Holland <samuel@sholland.org>
Link: https://lore.kernel.org/r/20220511192921.2223629-13-heiko@sntech.de
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/Kconfig

@@ -333,6 +333,12 @@ config RISCV_ALTERNATIVE
 	  code patching is performed once in the boot stages. It means
 	  that the overhead from this mechanism is just taken once.
 
+config RISCV_ALTERNATIVE_EARLY
+	bool
+	depends on RISCV_ALTERNATIVE
+	help
+	  Allows early patching of the kernel for special errata
+
 config RISCV_ISA_C
 	bool "Emit compressed instructions when building Linux"
 	default y

arch/riscv/Kconfig.erratas

@@ -33,4 +33,25 @@ config ERRATA_SIFIVE_CIP_1200
 
 	  If you don't know what to do here, say "Y".
 
+config ERRATA_THEAD
+	bool "T-HEAD errata"
+	select RISCV_ALTERNATIVE
+	help
+	  All T-HEAD errata Kconfig depend on this Kconfig. Disabling
+	  this Kconfig will disable all T-HEAD errata. Please say "Y"
+	  here if your platform uses T-HEAD CPU cores.
+
+	  Otherwise, please say "N" here to avoid unnecessary overhead.
+
+config ERRATA_THEAD_PBMT
+	bool "Apply T-Head memory type errata"
+	depends on ERRATA_THEAD && 64BIT
+	select RISCV_ALTERNATIVE_EARLY
+	default y
+	help
+	  This will apply the memory type errata to handle the non-standard
+	  memory type bits in page-table-entries on T-Head SoCs.
+
+	  If you don't know what to do here, say "Y".
+
 endmenu

arch/riscv/errata/Makefile

@@ -1 +1,2 @@
 obj-$(CONFIG_ERRATA_SIFIVE) += sifive/
+obj-$(CONFIG_ERRATA_THEAD) += thead/

arch/riscv/errata/sifive/errata.c

@@ -88,10 +88,15 @@ void __init_or_module sifive_errata_patch_func(struct alt_entry *begin,
 					       unsigned int stage)
 {
 	struct alt_entry *alt;
-	u32 cpu_req_errata = sifive_errata_probe(archid, impid);
+	u32 cpu_req_errata;
 	u32 cpu_apply_errata = 0;
 	u32 tmp;
 
+	if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
+		return;
+
+	cpu_req_errata = sifive_errata_probe(archid, impid);
+
 	for (alt = begin; alt < end; alt++) {
 		if (alt->vendor_id != SIFIVE_VENDOR_ID)
 			continue;

arch/riscv/errata/thead/Makefile

@@ -0,0 +1,11 @@
+ifdef CONFIG_RISCV_ALTERNATIVE_EARLY
+CFLAGS_errata.o := -mcmodel=medany
+ifdef CONFIG_FTRACE
+CFLAGS_REMOVE_errata.o = $(CC_FLAGS_FTRACE)
+endif
+ifdef CONFIG_KASAN
+KASAN_SANITIZE_errata.o := n
+endif
+endif
+
+obj-y += errata.o

arch/riscv/errata/thead/errata.c

@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2021 Heiko Stuebner <heiko@sntech.de>
+ */
+
+#include <linux/bug.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/uaccess.h>
+#include <asm/alternative.h>
+#include <asm/cacheflush.h>
+#include <asm/errata_list.h>
+#include <asm/patch.h>
+#include <asm/vendorid_list.h>
+
+struct errata_info {
+	char name[ERRATA_STRING_LENGTH_MAX];
+	bool (*check_func)(unsigned long arch_id, unsigned long impid);
+	unsigned int stage;
+};
+
+static bool errata_mt_check_func(unsigned long  arch_id, unsigned long impid)
+{
+	if (arch_id != 0 || impid != 0)
+		return false;
+	return true;
+}
+
+static const struct errata_info errata_list[ERRATA_THEAD_NUMBER] = {
+	{
+		.name = "memory-types",
+		.stage = RISCV_ALTERNATIVES_EARLY_BOOT,
+		.check_func = errata_mt_check_func
+	},
+};
+
+static u32 thead_errata_probe(unsigned int stage, unsigned long archid, unsigned long impid)
+{
+	const struct errata_info *info;
+	u32 cpu_req_errata = 0;
+	int idx;
+
+	for (idx = 0; idx < ERRATA_THEAD_NUMBER; idx++) {
+		info = &errata_list[idx];
+
+		if ((stage == RISCV_ALTERNATIVES_MODULE ||
+		     info->stage == stage) && info->check_func(archid, impid))
+			cpu_req_errata |= (1U << idx);
+	}
+
+	return cpu_req_errata;
+}
+
+void __init_or_module thead_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
+					      unsigned long archid, unsigned long impid,
+					      unsigned int stage)
+{
+	struct alt_entry *alt;
+	u32 cpu_req_errata = thead_errata_probe(stage, archid, impid);
+	u32 tmp;
+
+	for (alt = begin; alt < end; alt++) {
+		if (alt->vendor_id != THEAD_VENDOR_ID)
+			continue;
+		if (alt->errata_id >= ERRATA_THEAD_NUMBER)
+			continue;
+
+		tmp = (1U << alt->errata_id);
+		if (cpu_req_errata & tmp) {
+			/* On vm-alternatives, the mmu isn't running yet */
+			if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
+				memcpy((void *)__pa_symbol(alt->old_ptr),
+				       (void *)__pa_symbol(alt->alt_ptr), alt->alt_len);
+			else
+				patch_text_nosync(alt->old_ptr, alt->alt_ptr, alt->alt_len);
+		}
+	}
+
+	if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
+		local_flush_icache_all();
+}

arch/riscv/include/asm/alternative.h

@@ -21,8 +21,10 @@
 
 #define RISCV_ALTERNATIVES_BOOT		0 /* alternatives applied during regular boot */
 #define RISCV_ALTERNATIVES_MODULE	1 /* alternatives applied during module-init */
+#define RISCV_ALTERNATIVES_EARLY_BOOT	2 /* alternatives applied before mmu start */
 
 void __init apply_boot_alternatives(void);
+void __init apply_early_boot_alternatives(void);
 void apply_module_alternatives(void *start, size_t length);
 
 struct alt_entry {
@@ -41,6 +43,9 @@ struct errata_checkfunc_id {
 void sifive_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
 			      unsigned long archid, unsigned long impid,
 			      unsigned int stage);
+void thead_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
+			     unsigned long archid, unsigned long impid,
+			     unsigned int stage);
 
 void riscv_cpufeature_patch_func(struct alt_entry *begin, struct alt_entry *end,
 				 unsigned int stage);
@@ -48,6 +53,7 @@ void riscv_cpufeature_patch_func(struct alt_entry *begin, struct alt_entry *end,
 #else /* CONFIG_RISCV_ALTERNATIVE */
 
 static inline void apply_boot_alternatives(void) { }
+static inline void apply_early_boot_alternatives(void) { }
 static inline void apply_module_alternatives(void *start, size_t length) { }
 
 #endif /* CONFIG_RISCV_ALTERNATIVE */

arch/riscv/include/asm/errata_list.h

@@ -14,6 +14,11 @@
 #define	ERRATA_SIFIVE_NUMBER 2
 #endif
 
+#ifdef CONFIG_ERRATA_THEAD
+#define	ERRATA_THEAD_PBMT 0
+#define	ERRATA_THEAD_NUMBER 1
+#endif
+
 #define	CPUFEATURE_SVPBMT 0
 #define	CPUFEATURE_NUMBER 1
 
@@ -42,12 +47,51 @@ asm(ALTERNATIVE("sfence.vma %0", "sfence.vma", SIFIVE_VENDOR_ID,	\
  * in the default case.
  */
 #define ALT_SVPBMT_SHIFT 61
+#define ALT_THEAD_PBMT_SHIFT 59
 #define ALT_SVPBMT(_val, prot)						\
-asm(ALTERNATIVE("li %0, 0\t\nnop", "li %0, %1\t\nslli %0,%0,%2", 0,	\
-		CPUFEATURE_SVPBMT, CONFIG_RISCV_ISA_SVPBMT)		\
+asm(ALTERNATIVE_2("li %0, 0\t\nnop",					\
+		  "li %0, %1\t\nslli %0,%0,%3", 0,			\
+			CPUFEATURE_SVPBMT, CONFIG_RISCV_ISA_SVPBMT,	\
+		  "li %0, %2\t\nslli %0,%0,%4", THEAD_VENDOR_ID,	\
+			ERRATA_THEAD_PBMT, CONFIG_ERRATA_THEAD_PBMT)	\
 		: "=r"(_val)						\
 		: "I"(prot##_SVPBMT >> ALT_SVPBMT_SHIFT),		\
-		  "I"(ALT_SVPBMT_SHIFT))
+		  "I"(prot##_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
+		  "I"(ALT_SVPBMT_SHIFT),				\
+		  "I"(ALT_THEAD_PBMT_SHIFT))
+
+#ifdef CONFIG_ERRATA_THEAD_PBMT
+/*
+ * IO/NOCACHE memory types are handled together with svpbmt,
+ * so on T-Head chips, check if no other memory type is set,
+ * and set the non-0 PMA type if applicable.
+ */
+#define ALT_THEAD_PMA(_val)						\
+asm volatile(ALTERNATIVE(						\
+	"nop\n\t"							\
+	"nop\n\t"							\
+	"nop\n\t"							\
+	"nop\n\t"							\
+	"nop\n\t"							\
+	"nop\n\t"							\
+	"nop",								\
+	"li      t3, %2\n\t"						\
+	"slli    t3, t3, %4\n\t"					\
+	"and     t3, %0, t3\n\t"					\
+	"bne     t3, zero, 2f\n\t"					\
+	"li      t3, %3\n\t"						\
+	"slli    t3, t3, %4\n\t"					\
+	"or      %0, %0, t3\n\t"					\
+	"2:",  THEAD_VENDOR_ID,						\
+		ERRATA_THEAD_PBMT, CONFIG_ERRATA_THEAD_PBMT)		\
+	: "+r"(_val)							\
+	: "0"(_val),							\
+	  "I"(_PAGE_MTMASK_THEAD >> ALT_THEAD_PBMT_SHIFT),		\
+	  "I"(_PAGE_PMA_THEAD >> ALT_THEAD_PBMT_SHIFT),			\
+	  "I"(ALT_THEAD_PBMT_SHIFT))
+#else
+#define ALT_THEAD_PMA(_val)
+#endif
 
 #endif /* __ASSEMBLY__ */
 

arch/riscv/include/asm/pgtable-64.h

@@ -86,6 +86,18 @@ typedef struct {
 #define _PAGE_IO_SVPBMT		(1UL << 62)
 #define _PAGE_MTMASK_SVPBMT	(_PAGE_NOCACHE_SVPBMT | _PAGE_IO_SVPBMT)
 
+/*
+ * [63:59] T-Head Memory Type definitions:
+ *
+ * 00000 - NC   Weakly-ordered, Non-cacheable, Non-bufferable, Non-shareable, Non-trustable
+ * 01110 - PMA  Weakly-ordered, Cacheable, Bufferable, Shareable, Non-trustable
+ * 10000 - IO   Strongly-ordered, Non-cacheable, Non-bufferable, Non-shareable, Non-trustable
+ */
+#define _PAGE_PMA_THEAD		((1UL << 62) | (1UL << 61) | (1UL << 60))
+#define _PAGE_NOCACHE_THEAD	0UL
+#define _PAGE_IO_THEAD		(1UL << 63)
+#define _PAGE_MTMASK_THEAD	(_PAGE_PMA_THEAD | _PAGE_IO_THEAD | (1UL << 59))
+
 static inline u64 riscv_page_mtmask(void)
 {
 	u64 val;
@@ -193,7 +205,11 @@ static inline bool mm_pud_folded(struct mm_struct *mm)
 
 static inline pmd_t pfn_pmd(unsigned long pfn, pgprot_t prot)
 {
-	return __pmd((pfn << _PAGE_PFN_SHIFT) | pgprot_val(prot));
+	unsigned long prot_val = pgprot_val(prot);
+
+	ALT_THEAD_PMA(prot_val);
+
+	return __pmd((pfn << _PAGE_PFN_SHIFT) | prot_val);
 }
 
 static inline unsigned long _pmd_pfn(pmd_t pmd)

arch/riscv/include/asm/pgtable.h

@@ -250,7 +250,11 @@ static inline void pmd_clear(pmd_t *pmdp)
 
 static inline pgd_t pfn_pgd(unsigned long pfn, pgprot_t prot)
 {
-	return __pgd((pfn << _PAGE_PFN_SHIFT) | pgprot_val(prot));
+	unsigned long prot_val = pgprot_val(prot);
+
+	ALT_THEAD_PMA(prot_val);
+
+	return __pgd((pfn << _PAGE_PFN_SHIFT) | prot_val);
 }
 
 static inline unsigned long _pgd_pfn(pgd_t pgd)
@@ -289,7 +293,11 @@ static inline unsigned long pte_pfn(pte_t pte)
 /* Constructs a page table entry */
 static inline pte_t pfn_pte(unsigned long pfn, pgprot_t prot)
 {
-	return __pte((pfn << _PAGE_PFN_SHIFT) | pgprot_val(prot));
+	unsigned long prot_val = pgprot_val(prot);
+
+	ALT_THEAD_PMA(prot_val);
+
+	return __pte((pfn << _PAGE_PFN_SHIFT) | prot_val);
 }
 
 #define mk_pte(page, prot)       pfn_pte(page_to_pfn(page), prot)
@@ -398,7 +406,11 @@ static inline int pmd_protnone(pmd_t pmd)
 /* Modify page protection bits */
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
-	return __pte((pte_val(pte) & _PAGE_CHG_MASK) | pgprot_val(newprot));
+	unsigned long newprot_val = pgprot_val(newprot);
+
+	ALT_THEAD_PMA(newprot_val);
+
+	return __pte((pte_val(pte) & _PAGE_CHG_MASK) | newprot_val);
 }
 
 #define pgd_ERROR(e) \

arch/riscv/include/asm/vendorid_list.h

@@ -6,5 +6,6 @@
 #define ASM_VENDOR_LIST_H
 
 #define SIFIVE_VENDOR_ID	0x489
+#define THEAD_VENDOR_ID		0x5b7
 
 #endif

arch/riscv/kernel/Makefile

@@ -14,6 +14,20 @@ ifdef CONFIG_KEXEC
 AFLAGS_kexec_relocate.o := -mcmodel=medany $(call cc-option,-mno-relax)
 endif
 
+# cmodel=medany and notrace when patching early
+ifdef CONFIG_RISCV_ALTERNATIVE_EARLY
+CFLAGS_alternative.o := -mcmodel=medany
+CFLAGS_cpufeature.o := -mcmodel=medany
+ifdef CONFIG_FTRACE
+CFLAGS_REMOVE_alternative.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_cpufeature.o = $(CC_FLAGS_FTRACE)
+endif
+ifdef CONFIG_KASAN
+KASAN_SANITIZE_alternative.o := n
+KASAN_SANITIZE_cpufeature.o := n
+endif
+endif
+
 extra-y += head.o
 extra-y += vmlinux.lds
 

arch/riscv/kernel/alternative.c

@@ -42,6 +42,11 @@ static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_inf
 	case SIFIVE_VENDOR_ID:
 		cpu_mfr_info->vendor_patch_func = sifive_errata_patch_func;
 		break;
+#endif
+#ifdef CONFIG_ERRATA_THEAD
+	case THEAD_VENDOR_ID:
+		cpu_mfr_info->vendor_patch_func = thead_errata_patch_func;
+		break;
 #endif
 	default:
 		cpu_mfr_info->vendor_patch_func = NULL;
@@ -82,6 +87,27 @@ void __init apply_boot_alternatives(void)
 			    RISCV_ALTERNATIVES_BOOT);
 }
 
+/*
+ * apply_early_boot_alternatives() is called from setup_vm() with MMU-off.
+ *
+ * Following requirements should be honoured for it to work correctly:
+ * 1) It should use PC-relative addressing for accessing kernel symbols.
+ *    To achieve this we always use GCC cmodel=medany.
+ * 2) The compiler instrumentation for FTRACE will not work for setup_vm()
+ *    so disable compiler instrumentation when FTRACE is enabled.
+ *
+ * Currently, the above requirements are honoured by using custom CFLAGS
+ * for alternative.o in kernel/Makefile.
+ */
+void __init apply_early_boot_alternatives(void)
+{
+#ifdef CONFIG_RISCV_ALTERNATIVE_EARLY
+	_apply_alternatives((struct alt_entry *)__alt_start,
+			    (struct alt_entry *)__alt_end,
+			    RISCV_ALTERNATIVES_EARLY_BOOT);
+#endif
+}
+
 #ifdef CONFIG_MODULES
 void apply_module_alternatives(void *start, size_t length)
 {

arch/riscv/kernel/cpufeature.c

@@ -254,7 +254,12 @@ struct cpufeature_info {
 static bool __init_or_module cpufeature_svpbmt_check_func(unsigned int stage)
 {
 #ifdef CONFIG_RISCV_ISA_SVPBMT
-	return riscv_isa_extension_available(NULL, SVPBMT);
+	switch (stage) {
+	case RISCV_ALTERNATIVES_EARLY_BOOT:
+		return false;
+	default:
+		return riscv_isa_extension_available(NULL, SVPBMT);
+	}
 #endif
 
 	return false;

arch/riscv/mm/init.c

@@ -935,6 +935,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	BUG_ON((kernel_map.virt_addr + kernel_map.size) > ADDRESS_SPACE_END - SZ_4K);
 #endif
 
+	apply_early_boot_alternatives();
 	pt_ops_set_early();
 
 	/* Setup early PGD for fixmap */