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Subject[PATCH] riscv: toggle mmu_enabled flag in a precise manner
Date
From: Vitaly Wool <vitaly.wool@konsulko.com>

Cuurently mmu_enabled flag is set to true way later than the actual
MMU enablement takes place. This leads to hard-to-track races in
e. g. SBI earlycon initialization taking wrong path configuring
fixmap.

To fix that, move mmu_enabled toggling to head.S and rename it to
_mmu_enabled to avoid possible name clashes since it's not a static
variable any more.

Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.com>
---
arch/riscv/kernel/head.S | 9 +++++++++
arch/riscv/mm/init.c | 13 +++++--------
2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index 0a4e81b8dc79..33cd57285be3 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -248,6 +248,10 @@ clear_bss_done:
call relocate
#endif /* CONFIG_MMU */

+ la a0, _mmu_enabled
+ li a1, 1
+ sw a1, (a0)
+
call setup_trap_vector
/* Restore C environment */
la tp, init_task
@@ -370,6 +374,11 @@ ENTRY(reset_regs)
END(reset_regs)
#endif /* CONFIG_RISCV_M_MODE */

+.section ".data"
+ .global _mmu_enabled
+_mmu_enabled:
+ .word 0
+
__PAGE_ALIGNED_BSS
/* Empty zero page */
.balign PAGE_SIZE
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 787c75f751a5..4038be635e25 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -211,7 +211,7 @@ EXPORT_SYMBOL(pfn_base);
pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
-static bool mmu_enabled;
+extern bool _mmu_enabled;

#define MAX_EARLY_MAPPING_SIZE SZ_128M

@@ -236,7 +236,7 @@ void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)

static pte_t *__init get_pte_virt(phys_addr_t pa)
{
- if (mmu_enabled) {
+ if (_mmu_enabled) {
clear_fixmap(FIX_PTE);
return (pte_t *)set_fixmap_offset(FIX_PTE, pa);
} else {
@@ -250,7 +250,7 @@ static phys_addr_t __init alloc_pte(uintptr_t va)
* We only create PMD or PGD early mappings so we
* should never reach here with MMU disabled.
*/
- BUG_ON(!mmu_enabled);
+ BUG_ON(!_mmu_enabled);

return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
}
@@ -281,7 +281,7 @@ pmd_t early_pmd[PTRS_PER_PMD * NUM_EARLY_PMDS] __initdata __aligned(PAGE_SIZE);

static pmd_t *__init get_pmd_virt(phys_addr_t pa)
{
- if (mmu_enabled) {
+ if (_mmu_enabled) {
clear_fixmap(FIX_PMD);
return (pmd_t *)set_fixmap_offset(FIX_PMD, pa);
} else {
@@ -293,7 +293,7 @@ static phys_addr_t __init alloc_pmd(uintptr_t va)
{
uintptr_t pmd_num;

- if (mmu_enabled)
+ if (_mmu_enabled)
return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);

pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
@@ -467,9 +467,6 @@ static void __init setup_vm_final(void)
phys_addr_t pa, start, end;
struct memblock_region *reg;

- /* Set mmu_enabled flag */
- mmu_enabled = true;
-
/* Setup swapper PGD for fixmap */
create_pgd_mapping(swapper_pg_dir, FIXADDR_START,
__pa_symbol(fixmap_pgd_next),
--
2.20.1
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