[PATCH v7 13/23] arm64: cpufeature: Add an early command-line cpufeature override facility

Marc Zyngier
2021-02-08T10:22:28Z

In order to be able to override CPU features at boot time,
let's add a command line parser that matches options of the
form "cpureg.feature=value", and store the corresponding
value into the override val/mask pair.

No features are currently defined, so no expected change in
functionality.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: David Brazdil <dbrazdil@google.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
arch/arm64/kernel/Makefile | 2 +-
arch/arm64/kernel/head.S | 1 +
arch/arm64/kernel/idreg-override.c | 150 +++++++++++++++++++++++++++++
3 files changed, 152 insertions(+), 1 deletion(-)
create mode 100644 arch/arm64/kernel/idreg-override.c

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 86364ab6f13f..2262f0392857 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -17,7 +17,7 @@ obj-y := debug-monitors.o entry.o irq.o fpsimd.o \
return_address.o cpuinfo.o cpu_errata.o \
cpufeature.o alternative.o cacheinfo.o \
smp.o smp_spin_table.o topology.o smccc-call.o \
- syscall.o proton-pack.o
+ syscall.o proton-pack.o idreg-override.o

targets += efi-entry.o

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index d74e5f84042e..3243e3ae9bd8 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -435,6 +435,7 @@ SYM_FUNC_START_LOCAL(__primary_switched)

mov x0, x21 // pass FDT address in x0
bl early_fdt_map // Try mapping the FDT early
+ bl init_feature_override
bl switch_to_vhe
#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
bl kasan_early_init
diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
new file mode 100644
index 000000000000..3a347b42d07e
--- /dev/null
+++ b/arch/arm64/kernel/idreg-override.c
@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Early cpufeature override framework
+ *
+ * Copyright (C) 2020 Google LLC
+ * Author: Marc Zyngier <maz@kernel.org>
+ */
+
+#include <linux/ctype.h>
+#include <linux/kernel.h>
+#include <linux/libfdt.h>
+
+#include <asm/cacheflush.h>
+#include <asm/setup.h>
+
+#define FTR_DESC_NAME_LEN 20
+#define FTR_DESC_FIELD_LEN 10
+
+struct ftr_set_desc {
+ char name[FTR_DESC_NAME_LEN];
+ struct arm64_ftr_override *override;
+ struct {
+ char name[FTR_DESC_FIELD_LEN];
+ u8 shift;
+ } fields[];
+};
+
+static const struct ftr_set_desc * const regs[] __initconst = {
+};
+
+static int __init find_field(const char *cmdline,
+ const struct ftr_set_desc *reg, int f, u64 *v)
+{
+ char opt[FTR_DESC_NAME_LEN + FTR_DESC_FIELD_LEN + 2];
+ int len;
+
+ len = snprintf(opt, ARRAY_SIZE(opt), "%s.%s=",
+ reg->name, reg->fields[f].name);
+
+ if (!parameqn(cmdline, opt, len))
+ return -1;
+
+ return kstrtou64(cmdline + len, 0, v);
+}
+
+static void __init match_options(const char *cmdline)
+{
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(regs); i++) {
+ int f;
+
+ if (!regs[i]->override)
+ continue;
+
+ for (f = 0; strlen(regs[i]->fields[f].name); f++) {
+ u64 shift = regs[i]->fields[f].shift;
+ u64 mask = 0xfUL << shift;
+ u64 v;
+
+ if (find_field(cmdline, regs[i], f, &v))
+ continue;
+
+ regs[i]->override->val &= ~mask;
+ regs[i]->override->val |= (v << shift) & mask;
+ regs[i]->override->mask |= mask;
+
+ return;
+ }
+ }
+}
+
+static __init void __parse_cmdline(const char *cmdline)
+{
+ do {
+ char buf[256];
+ size_t len;
+ int i;
+
+ cmdline = skip_spaces(cmdline);
+
+ for (len = 0; cmdline[len] && !isspace(cmdline[len]); len++);
+ if (!len)
+ return;
+
+ len = min(len, ARRAY_SIZE(buf) - 1);
+ strncpy(buf, cmdline, len);
+ buf[len] = 0;
+
+ if (strcmp(buf, "--") == 0)
+ return;
+
+ cmdline += len;
+
+ match_options(buf);
+
+ } while (1);
+}
+
+static __init void parse_cmdline(void)
+{
+ if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
+ const u8 *prop;
+ void *fdt;
+ int node;
+
+ fdt = get_early_fdt_ptr();
+ if (!fdt)
+ goto out;
+
+ node = fdt_path_offset(fdt, "/chosen");
+ if (node < 0)
+ goto out;
+
+ prop = fdt_getprop(fdt, node, "bootargs", NULL);
+ if (!prop)
+ goto out;
+
+ __parse_cmdline(prop);
+
+ if (!IS_ENABLED(CONFIG_CMDLINE_EXTEND))
+ return;
+ }
+
+out:
+ __parse_cmdline(CONFIG_CMDLINE);
+}
+
+/* Keep checkers quiet */
+void init_feature_override(void);
+
+asmlinkage void __init init_feature_override(void)
+{
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(regs); i++) {
+ if (regs[i]->override) {
+ regs[i]->override->val = 0;
+ regs[i]->override->mask = 0;
+ }
+ }
+
+ parse_cmdline();
+
+ for (i = 0; i < ARRAY_SIZE(regs); i++) {
+ if (regs[i]->override)
+ __flush_dcache_area(regs[i]->override,
+ sizeof(*regs[i]->override));
+ }
+}
--
2.29.2