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SubjectRe: [PATCH] riscv: toggle mmu_enabled flag in a precise manner
On Tue, Dec 1, 2020 at 1:01 AM <vitaly.wool@konsulko.com> wrote:
>
> 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.
>

This code path is significantly changed in 5.10-rcX with UEFI series.
https://patchwork.kernel.org/project/linux-riscv/patch/20200917223716.2300238-4-atish.patra@wdc.com/

Can you check if you can still reproduce the issue you were seeing
with the latest upstream kernel ?
If yes, please share the steps to reproduce the issue.

> 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
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv



--
Regards,
Atish

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