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Message-ID: <mhng-163a2157-ae6c-424e-b3f1-581364f7650a@palmerdabbelt-glaptop1>
Date: Sat, 15 Aug 2020 15:39:37 -0700 (PDT)
From: Palmer Dabbelt <palmer@...belt.com>
To: Atish Patra <Atish.Patra@....com>
CC: linux-kernel@...r.kernel.org, Anup Patel <Anup.Patel@....com>,
Atish Patra <Atish.Patra@....com>, aou@...s.berkeley.edu,
Alistair Francis <Alistair.Francis@....com>,
akpm@...ux-foundation.org, ardb@...nel.org, nivedita@...m.mit.edu,
bp@...e.de, greentime.hu@...ive.com, mingo@...nel.org,
keescook@...omium.org, linux-efi@...r.kernel.org,
linux-riscv@...ts.infradead.org, fwts-devel@...ts.ubuntu.com,
han_mao@...ky.com, masahiroy@...nel.org, michal.simek@...inx.com,
rppt@...nel.org, Nick Desaulniers <ndesaulniers@...gle.com>,
Paul Walmsley <paul.walmsley@...ive.com>, steven.price@....com,
longman@...hat.com, will@...nel.org, daniel.schaefer@....com,
abner.chang@....com
Subject: Re: [PATCH v5 1/9] RISC-V: Move DT mapping outof fixmap
On Wed, 12 Aug 2020 16:47:50 PDT (-0700), Atish Patra wrote:
> From: Anup Patel <anup.patel@....com>
>
> Currently, RISC-V reserves 1MB of fixmap memory for device tree. However,
> it maps only single PMD (2MB) space for fixmap which leaves only < 1MB space
> left for other kernel features such as early ioremap which requires fixmap
> as well. The fixmap size can be increased by another 2MB but it brings
> additional complexity and changes the virtual memory layout as well.
> If we require some additional feature requiring fixmap again, it has to be
> moved again.
>
> Technically, DT doesn't need a fixmap as the memory occupied by the DT is
> only used during boot. That's why, We map device tree in early page table
> using two consecutive PGD mappings at lower addresses (< PAGE_OFFSET).
> This frees lot of space in fixmap and also makes maximum supported
> device tree size supported as PGDIR_SIZE. Thus, init memory section can be used
> for the same purpose as well. This simplifies fixmap implementation.
>
> Signed-off-by: Anup Patel <anup.patel@....com>
> Signed-off-by: Atish Patra <atish.patra@....com>
> ---
> arch/riscv/include/asm/fixmap.h | 3 ---
> arch/riscv/include/asm/pgtable.h | 1 +
> arch/riscv/kernel/head.S | 1 -
> arch/riscv/kernel/head.h | 2 --
> arch/riscv/kernel/setup.c | 9 +++++++--
> arch/riscv/mm/init.c | 26 ++++++++++++--------------
> 6 files changed, 20 insertions(+), 22 deletions(-)
>
> diff --git a/arch/riscv/include/asm/fixmap.h b/arch/riscv/include/asm/fixmap.h
> index 1ff075a8dfc7..11613f38228a 100644
> --- a/arch/riscv/include/asm/fixmap.h
> +++ b/arch/riscv/include/asm/fixmap.h
> @@ -22,9 +22,6 @@
> */
> enum fixed_addresses {
> FIX_HOLE,
> -#define FIX_FDT_SIZE SZ_1M
> - FIX_FDT_END,
> - FIX_FDT = FIX_FDT_END + FIX_FDT_SIZE / PAGE_SIZE - 1,
> FIX_PTE,
> FIX_PMD,
> FIX_TEXT_POKE1,
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index eaea1f717010..815f8c959dd4 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -464,6 +464,7 @@ static inline void __kernel_map_pages(struct page *page, int numpages, int enabl
> #define kern_addr_valid(addr) (1) /* FIXME */
>
> extern void *dtb_early_va;
> +extern uintptr_t dtb_early_pa;
> void setup_bootmem(void);
> void paging_init(void);
>
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 7822054dbd88..a2f0cb3ca0a6 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -255,7 +255,6 @@ clear_bss_done:
> #endif
> /* Start the kernel */
> call soc_early_init
> - call parse_dtb
> tail start_kernel
>
> .Lsecondary_start:
> diff --git a/arch/riscv/kernel/head.h b/arch/riscv/kernel/head.h
> index 105fb0496b24..b48dda3d04f6 100644
> --- a/arch/riscv/kernel/head.h
> +++ b/arch/riscv/kernel/head.h
> @@ -16,6 +16,4 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa);
> extern void *__cpu_up_stack_pointer[];
> extern void *__cpu_up_task_pointer[];
>
> -void __init parse_dtb(void);
> -
> #endif /* __ASM_HEAD_H */
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index f04373be54a6..6a0ee2405813 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -49,8 +49,9 @@ atomic_t hart_lottery __section(.sdata);
> unsigned long boot_cpu_hartid;
> static DEFINE_PER_CPU(struct cpu, cpu_devices);
>
> -void __init parse_dtb(void)
> +static void __init parse_dtb(void)
> {
> + /* Early scan of device tree from init memory */
> if (early_init_dt_scan(dtb_early_va))
> return;
>
> @@ -63,6 +64,7 @@ void __init parse_dtb(void)
>
> void __init setup_arch(char **cmdline_p)
> {
> + parse_dtb();
> init_mm.start_code = (unsigned long) _stext;
> init_mm.end_code = (unsigned long) _etext;
> init_mm.end_data = (unsigned long) _edata;
> @@ -77,7 +79,10 @@ void __init setup_arch(char **cmdline_p)
> #if IS_ENABLED(CONFIG_BUILTIN_DTB)
> unflatten_and_copy_device_tree();
> #else
> - unflatten_device_tree();
> + if (early_init_dt_verify(__va(dtb_early_pa)))
> + unflatten_device_tree();
> + else
> + pr_err("No DTB found in kernel mappings\n");
> #endif
> clint_init_boot_cpu();
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 787c75f751a5..2b651f63f5c4 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -28,7 +28,9 @@ unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
> EXPORT_SYMBOL(empty_zero_page);
>
> extern char _start[];
> -void *dtb_early_va;
> +#define DTB_EARLY_BASE_VA PGDIR_SIZE
> +void *dtb_early_va __initdata;
> +uintptr_t dtb_early_pa __initdata;
>
> static void __init zone_sizes_init(void)
> {
> @@ -141,8 +143,6 @@ static void __init setup_initrd(void)
> }
> #endif /* CONFIG_BLK_DEV_INITRD */
>
> -static phys_addr_t dtb_early_pa __initdata;
> -
> void __init setup_bootmem(void)
> {
> struct memblock_region *reg;
> @@ -399,7 +399,7 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
>
> asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> {
> - uintptr_t va, end_va;
> + uintptr_t va, pa, end_va;
> uintptr_t load_pa = (uintptr_t)(&_start);
> uintptr_t load_sz = (uintptr_t)(&_end) - load_pa;
> uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
> @@ -448,16 +448,13 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> load_pa + (va - PAGE_OFFSET),
> map_size, PAGE_KERNEL_EXEC);
>
> - /* Create fixed mapping for early FDT parsing */
> - end_va = __fix_to_virt(FIX_FDT) + FIX_FDT_SIZE;
> - for (va = __fix_to_virt(FIX_FDT); va < end_va; va += PAGE_SIZE)
> - create_pte_mapping(fixmap_pte, va,
> - dtb_pa + (va - __fix_to_virt(FIX_FDT)),
> - PAGE_SIZE, PAGE_KERNEL);
> -
> - /* Save pointer to DTB for early FDT parsing */
> - dtb_early_va = (void *)fix_to_virt(FIX_FDT) + (dtb_pa & ~PAGE_MASK);
> - /* Save physical address for memblock reservation */
> + /* Create two consecutive PGD mappings for FDT early scan */
> + pa = dtb_pa & ~(PGDIR_SIZE - 1);
> + create_pgd_mapping(early_pg_dir, DTB_EARLY_BASE_VA,
> + pa, PGDIR_SIZE, PAGE_KERNEL);
> + create_pgd_mapping(early_pg_dir, DTB_EARLY_BASE_VA + PGDIR_SIZE,
> + pa + PGDIR_SIZE, PGDIR_SIZE, PAGE_KERNEL);
> + dtb_early_va = (void *)DTB_EARLY_BASE_VA + (dtb_pa & (PGDIR_SIZE - 1));
> dtb_early_pa = dtb_pa;
> }
>
> @@ -516,6 +513,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> #else
> dtb_early_va = (void *)dtb_pa;
> #endif
> + dtb_early_pa = dtb_pa;
> }
>
> static inline void setup_vm_final(void)
Reviewed-by: Palmer Dabbelt <palmerdabbelt@...gle.com>
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