[PATCH 11/12] riscv: don't use global static vars to store alternative data

Heiko Stuebner
2022-05-11T19:31:43Z

Right now the code uses a global struct to store vendor-ids
and another global variable to store the vendor-patch-function.

There exist specific cases where we'll need to patch the kernel
at an even earlier stage, where trying to write to a static
variable might actually result in hangs.

Also collecting the vendor-information consists of 3 sbi-ecalls
(or csr-reads) which is pretty negligible in the context of
booting a kernel.

So rework the code to not rely on static variables and instead
collect the vendor-information when a round of alternatives is
to be applied.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
---
arch/riscv/kernel/alternative.c | 51 ++++++++++++++++-----------------
1 file changed, 24 insertions(+), 27 deletions(-)

diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
index e6c9de9f9ba6..27f722ae452b 100644
--- a/arch/riscv/kernel/alternative.c
+++ b/arch/riscv/kernel/alternative.c
@@ -16,41 +16,35 @@
#include <asm/sbi.h>
#include <asm/csr.h>

-static struct cpu_manufacturer_info_t {
+struct cpu_manufacturer_info_t {
unsigned long vendor_id;
unsigned long arch_id;
unsigned long imp_id;
-} cpu_mfr_info;
+ void (*vendor_patch_func)(struct alt_entry *begin, struct alt_entry *end,
+ unsigned long archid, unsigned long impid,
+ unsigned int stage);
+};

-static void (*vendor_patch_func)(struct alt_entry *begin, struct alt_entry *end,
- unsigned long archid, unsigned long impid,
- unsigned int stage) __initdata_or_module;
-
-static inline void __init riscv_fill_cpu_mfr_info(void)
+static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_info_t *cpu_mfr_info)
{
#ifdef CONFIG_RISCV_M_MODE
- cpu_mfr_info.vendor_id = csr_read(CSR_MVENDORID);
- cpu_mfr_info.arch_id = csr_read(CSR_MARCHID);
- cpu_mfr_info.imp_id = csr_read(CSR_MIMPID);
+ cpu_mfr_info->vendor_id = csr_read(CSR_MVENDORID);
+ cpu_mfr_info->arch_id = csr_read(CSR_MARCHID);
+ cpu_mfr_info->imp_id = csr_read(CSR_MIMPID);
#else
- cpu_mfr_info.vendor_id = sbi_get_mvendorid();
- cpu_mfr_info.arch_id = sbi_get_marchid();
- cpu_mfr_info.imp_id = sbi_get_mimpid();
+ cpu_mfr_info->vendor_id = sbi_get_mvendorid();
+ cpu_mfr_info->arch_id = sbi_get_marchid();
+ cpu_mfr_info->imp_id = sbi_get_mimpid();
#endif
-}
-
-static void __init init_alternative(void)
-{
- riscv_fill_cpu_mfr_info();

- switch (cpu_mfr_info.vendor_id) {
+ switch (cpu_mfr_info->vendor_id) {
#ifdef CONFIG_ERRATA_SIFIVE
case SIFIVE_VENDOR_ID:
- vendor_patch_func = sifive_errata_patch_func;
+ cpu_mfr_info->vendor_patch_func = sifive_errata_patch_func;
break;
#endif
default:
- vendor_patch_func = NULL;
+ cpu_mfr_info->vendor_patch_func = NULL;
}
}

@@ -63,14 +57,19 @@ static void __init_or_module _apply_alternatives(struct alt_entry *begin,
struct alt_entry *end,
unsigned int stage)
{
+ struct cpu_manufacturer_info_t cpu_mfr_info;
+
+ riscv_fill_cpu_mfr_info(&cpu_mfr_info);
+
riscv_cpufeature_patch_func(begin, end, stage);

- if (!vendor_patch_func)
+ if (!cpu_mfr_info.vendor_patch_func)
return;

- vendor_patch_func(begin, end,
- cpu_mfr_info.arch_id, cpu_mfr_info.imp_id,
- stage);
+ cpu_mfr_info.vendor_patch_func(begin, end,
+ cpu_mfr_info.arch_id,
+ cpu_mfr_info.imp_id,
+ stage);
}

void __init apply_boot_alternatives(void)
@@ -78,8 +77,6 @@ void __init apply_boot_alternatives(void)
/* If called on non-boot cpu things could go wrong */
WARN_ON(smp_processor_id() != 0);

- init_alternative();
-
_apply_alternatives((struct alt_entry *)__alt_start,
(struct alt_entry *)__alt_end,
RISCV_ALTERNATIVES_BOOT);
--
2.35.1