Hey Alex!
On Thu, Mar 23, 2023 at 05:33:46PM +0100, Alexandre Ghiti wrote:
> riscv establishes 2 virtual mappings:
>
> - early_pg_dir maps the kernel which allows to discover the system
> memory
> - swapper_pg_dir installs the final mapping (linear mapping included)
>
> We used to map the dtb in early_pg_dir using DTB_EARLY_BASE_VA, and this
> mapping was not carried over in swapper_pg_dir. It happens that
> early_init_fdt_scan_reserved_mem must be called before swapper_pg_dir is
> setup otherwise we could allocate reserved memory defined in the dtb.
> And this function initializes reserved_mem variable with addresses that
> lie in the early_pg_dir dtb mapping: when those addresses are reused
> with swapper_pg_dir, this mapping does not exist and then we trap.
>
> So move the dtb mapping in the fixmap region which is established in
> early_pg_dir and handed over to swapper_pg_dir.
So I think this does a good job of explaining why we had a problem with
reserved memory to begin with, but I think it would be good to explain
exactly where
> Fixes: 50e63dd8ed92 ("riscv: fix reserved memory setup")
gets things wrong. That being, as far as I can tell, that it violates
the requirement "...must be called before swapper_pg_dir is set up".
It would be good to mention that specifically I think, say:
riscv establishes 2 virtual mappings:
- early_pg_dir maps the kernel which allows to discover the system
memory
- swapper_pg_dir installs the final mapping (linear mapping included)
We used to map the dtb in early_pg_dir using DTB_EARLY_BASE_VA, and this
mapping was not carried over in swapper_pg_dir. This caused problems
for reserved memory, as early_init_fdt_scan_reserved_mem() initialised
reserved_mem variables with addresses that lie in the early_pg_dir dtb
mapping. When those addresses are reused with swapper_pg_dir, this
mapping does not exist and then we trap.
The previous "fix" was incorrect as early_init_fdt_scan_reserved_mem()
must be called before swapper_pg_dir is set up otherwise we could
allocate in reserved memory defined in the dtb.
Move the dtb mapping in the fixmap region which is established in
early_pg_dir and handed over to swapper_pg_dir.
You need this one too:
Fixes: 922b0375fc93 ("riscv: Fix memblock reservation for device tree blob")
As an aside, one thing I noticed while re-working that, would you mind
adding ()s to function names in commit messages? Makes differentiation
between functions and variables etc a lot easier :)
This is probably the least confident R-b I've given to date:
Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
But I did also run this through the test the trigger the initial
problems and it looks good, so:
Tested-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> Reported-by: Conor Dooley <Conor.Dooley@xxxxxxxxxxxxx>
btw, could you make the email all lowercase if you re-spin, exchange did
what it does to the original report cos it was sent from Thunderbird
rather than mutt.
Thanks for working on this,
Conor.
> Link: https://lore.kernel.org/all/f8e67f82-103d-156c-deb0-d6d6e2756f5e@xxxxxxxxxxxxx/
> Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> ---
> Documentation/riscv/vm-layout.rst | 6 +--
> arch/riscv/include/asm/fixmap.h | 8 ++++
> arch/riscv/include/asm/pgtable.h | 8 +++-
> arch/riscv/kernel/setup.c | 1 -
> arch/riscv/mm/init.c | 61 +++++++++++++++++--------------
> 5 files changed, 51 insertions(+), 33 deletions(-)
>
> diff --git a/Documentation/riscv/vm-layout.rst b/Documentation/riscv/vm-layout.rst
> index 3be44e74ec5d..5462c84f4723 100644
> --- a/Documentation/riscv/vm-layout.rst
> +++ b/Documentation/riscv/vm-layout.rst
> @@ -47,7 +47,7 @@ RISC-V Linux Kernel SV39
> | Kernel-space virtual memory, shared between all processes:
> ____________________________________________________________|___________________________________________________________
> | | | |
> - ffffffc6fee00000 | -228 GB | ffffffc6feffffff | 2 MB | fixmap
> + ffffffc6fea00000 | -228 GB | ffffffc6feffffff | 6 MB | fixmap
> ffffffc6ff000000 | -228 GB | ffffffc6ffffffff | 16 MB | PCI io
> ffffffc700000000 | -228 GB | ffffffc7ffffffff | 4 GB | vmemmap
> ffffffc800000000 | -224 GB | ffffffd7ffffffff | 64 GB | vmalloc/ioremap space
> @@ -83,7 +83,7 @@ RISC-V Linux Kernel SV48
> | Kernel-space virtual memory, shared between all processes:
> ____________________________________________________________|___________________________________________________________
> | | | |
> - ffff8d7ffee00000 | -114.5 TB | ffff8d7ffeffffff | 2 MB | fixmap
> + ffff8d7ffea00000 | -114.5 TB | ffff8d7ffeffffff | 6 MB | fixmap
> ffff8d7fff000000 | -114.5 TB | ffff8d7fffffffff | 16 MB | PCI io
> ffff8d8000000000 | -114.5 TB | ffff8f7fffffffff | 2 TB | vmemmap
> ffff8f8000000000 | -112.5 TB | ffffaf7fffffffff | 32 TB | vmalloc/ioremap space
> @@ -119,7 +119,7 @@ RISC-V Linux Kernel SV57
> | Kernel-space virtual memory, shared between all processes:
> ____________________________________________________________|___________________________________________________________
> | | | |
> - ff1bfffffee00000 | -57 PB | ff1bfffffeffffff | 2 MB | fixmap
> + ff1bfffffea00000 | -57 PB | ff1bfffffeffffff | 6 MB | fixmap
> ff1bffffff000000 | -57 PB | ff1bffffffffffff | 16 MB | PCI io
> ff1c000000000000 | -57 PB | ff1fffffffffffff | 1 PB | vmemmap
> ff20000000000000 | -56 PB | ff5fffffffffffff | 16 PB | vmalloc/ioremap space
> diff --git a/arch/riscv/include/asm/fixmap.h b/arch/riscv/include/asm/fixmap.h
> index 5c3e7b97fcc6..0a55099bb734 100644
> --- a/arch/riscv/include/asm/fixmap.h
> +++ b/arch/riscv/include/asm/fixmap.h
> @@ -22,6 +22,14 @@
> */
> enum fixed_addresses {
> FIX_HOLE,
> + /*
> + * The fdt fixmap mapping must be PMD aligned and will be mapped
> + * using PMD entries in fixmap_pmd in 64-bit and a PGD entry in 32-bit.
> + */
> + FIX_FDT_END,
> + FIX_FDT = FIX_FDT_END + FIX_FDT_SIZE / PAGE_SIZE - 1,
> +
> + /* Below fixmaps will be mapped using fixmap_pte */
> FIX_PTE,
> FIX_PMD,
> FIX_PUD,
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index ab05f892d317..f641837ccf31 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -87,9 +87,13 @@
>
> #define FIXADDR_TOP PCI_IO_START
> #ifdef CONFIG_64BIT
> -#define FIXADDR_SIZE PMD_SIZE
> +#define MAX_FDT_SIZE PMD_SIZE
> +#define FIX_FDT_SIZE (MAX_FDT_SIZE + SZ_2M)
> +#define FIXADDR_SIZE (PMD_SIZE + FIX_FDT_SIZE)
> #else
> -#define FIXADDR_SIZE PGDIR_SIZE
> +#define MAX_FDT_SIZE PGDIR_SIZE
> +#define FIX_FDT_SIZE MAX_FDT_SIZE
> +#define FIXADDR_SIZE (PGDIR_SIZE + FIX_FDT_SIZE)
> #endif
> #define FIXADDR_START (FIXADDR_TOP - FIXADDR_SIZE)
>
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 376d2827e736..542eed85ad2c 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -283,7 +283,6 @@ void __init setup_arch(char **cmdline_p)
> else
> pr_err("No DTB found in kernel mappings\n");
> #endif
> - early_init_fdt_scan_reserved_mem();
> misc_mem_init();
>
> init_resources();
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 478d6763a01a..fb78d6bbabae 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -57,7 +57,6 @@ unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
> EXPORT_SYMBOL(empty_zero_page);
>
> extern char _start[];
> -#define DTB_EARLY_BASE_VA PGDIR_SIZE
> void *_dtb_early_va __initdata;
> uintptr_t _dtb_early_pa __initdata;
>
> @@ -236,6 +235,14 @@ static void __init setup_bootmem(void)
> set_max_mapnr(max_low_pfn - ARCH_PFN_OFFSET);
>
> reserve_initrd_mem();
> +
> + /*
> + * No allocation should be done before reserving the memory as defined
> + * in the device tree, otherwise the allocation could end up in a
> + * reserved region.
> + */
> + early_init_fdt_scan_reserved_mem();
> +
> /*
> * If DTB is built in, no need to reserve its memblock.
> * Otherwise, do reserve it but avoid using
> @@ -279,9 +286,6 @@ pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
> static pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
>
> pgd_t early_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
> -static p4d_t __maybe_unused early_dtb_p4d[PTRS_PER_P4D] __initdata __aligned(PAGE_SIZE);
> -static pud_t __maybe_unused early_dtb_pud[PTRS_PER_PUD] __initdata __aligned(PAGE_SIZE);
> -static pmd_t __maybe_unused early_dtb_pmd[PTRS_PER_PMD] __initdata __aligned(PAGE_SIZE);
>
> #ifdef CONFIG_XIP_KERNEL
> #define pt_ops (*(struct pt_alloc_ops *)XIP_FIXUP(&pt_ops))
> @@ -626,9 +630,6 @@ static void __init create_p4d_mapping(p4d_t *p4dp,
> #define trampoline_pgd_next (pgtable_l5_enabled ? \
> (uintptr_t)trampoline_p4d : (pgtable_l4_enabled ? \
> (uintptr_t)trampoline_pud : (uintptr_t)trampoline_pmd))
> -#define early_dtb_pgd_next (pgtable_l5_enabled ? \
> - (uintptr_t)early_dtb_p4d : (pgtable_l4_enabled ? \
> - (uintptr_t)early_dtb_pud : (uintptr_t)early_dtb_pmd))
> #else
> #define pgd_next_t pte_t
> #define alloc_pgd_next(__va) pt_ops.alloc_pte(__va)
> @@ -636,7 +637,6 @@ static void __init create_p4d_mapping(p4d_t *p4dp,
> #define create_pgd_next_mapping(__nextp, __va, __pa, __sz, __prot) \
> create_pte_mapping(__nextp, __va, __pa, __sz, __prot)
> #define fixmap_pgd_next ((uintptr_t)fixmap_pte)
> -#define early_dtb_pgd_next ((uintptr_t)early_dtb_pmd)
> #define create_p4d_mapping(__pmdp, __va, __pa, __sz, __prot) do {} while(0)
> #define create_pud_mapping(__pmdp, __va, __pa, __sz, __prot) do {} while(0)
> #define create_pmd_mapping(__pmdp, __va, __pa, __sz, __prot) do {} while(0)
> @@ -860,32 +860,28 @@ static void __init create_kernel_page_table(pgd_t *pgdir, bool early)
> * this means 2 PMD entries whereas for 32-bit kernel, this is only 1 PGDIR
> * entry.
> */
> -static void __init create_fdt_early_page_table(pgd_t *pgdir, uintptr_t dtb_pa)
> +static void __init create_fdt_early_page_table(pgd_t *pgdir,
> + uintptr_t fix_fdt_va,
> + uintptr_t dtb_pa)
> {
> -#ifndef CONFIG_BUILTIN_DTB
> uintptr_t pa = dtb_pa & ~(PMD_SIZE - 1);
>
> - create_pgd_mapping(early_pg_dir, DTB_EARLY_BASE_VA,
> - IS_ENABLED(CONFIG_64BIT) ? early_dtb_pgd_next : pa,
> - PGDIR_SIZE,
> - IS_ENABLED(CONFIG_64BIT) ? PAGE_TABLE : PAGE_KERNEL);
> -
> - if (pgtable_l5_enabled)
> - create_p4d_mapping(early_dtb_p4d, DTB_EARLY_BASE_VA,
> - (uintptr_t)early_dtb_pud, P4D_SIZE, PAGE_TABLE);
> -
> - if (pgtable_l4_enabled)
> - create_pud_mapping(early_dtb_pud, DTB_EARLY_BASE_VA,
> - (uintptr_t)early_dtb_pmd, PUD_SIZE, PAGE_TABLE);
> +#ifndef CONFIG_BUILTIN_DTB
> + /* Make sure the fdt fixmap address is always aligned on PMD size */
> + BUILD_BUG_ON(FIX_FDT % (PMD_SIZE / PAGE_SIZE));
>
> - if (IS_ENABLED(CONFIG_64BIT)) {
> - create_pmd_mapping(early_dtb_pmd, DTB_EARLY_BASE_VA,
> + /* In 32-bit only, the fdt lies in its own PGD */
> + if (!IS_ENABLED(CONFIG_64BIT)) {
> + create_pgd_mapping(early_pg_dir, fix_fdt_va,
> + pa, MAX_FDT_SIZE, PAGE_KERNEL);
> + } else {
> + create_pmd_mapping(fixmap_pmd, fix_fdt_va,
> pa, PMD_SIZE, PAGE_KERNEL);
> - create_pmd_mapping(early_dtb_pmd, DTB_EARLY_BASE_VA + PMD_SIZE,
> + create_pmd_mapping(fixmap_pmd, fix_fdt_va + PMD_SIZE,
> pa + PMD_SIZE, PMD_SIZE, PAGE_KERNEL);
> }
>
> - dtb_early_va = (void *)DTB_EARLY_BASE_VA + (dtb_pa & (PMD_SIZE - 1));
> + dtb_early_va = (void *)fix_fdt_va + (dtb_pa & (PMD_SIZE - 1));
> #else
> /*
> * For 64-bit kernel, __va can't be used since it would return a linear
> @@ -1055,7 +1051,8 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> create_kernel_page_table(early_pg_dir, true);
>
> /* Setup early mapping for FDT early scan */
> - create_fdt_early_page_table(early_pg_dir, dtb_pa);
> + create_fdt_early_page_table(early_pg_dir,
> + __fix_to_virt(FIX_FDT), dtb_pa);
>
> /*
> * Bootime fixmap only can handle PMD_SIZE mapping. Thus, boot-ioremap
> @@ -1097,6 +1094,16 @@ static void __init setup_vm_final(void)
> u64 i;
>
> /* Setup swapper PGD for fixmap */
> +#if !defined(CONFIG_64BIT)
> + /*
> + * In 32-bit, the device tree lies in a pgd entry, so it must be copied
> + * directly in swapper_pg_dir in addition to the pgd entry that points
> + * to fixmap_pte.
> + */
> + unsigned long idx = pgd_index(__fix_to_virt(FIX_FDT));
> +
> + set_pgd(&swapper_pg_dir[idx], early_pg_dir[idx]);
> +#endif
> create_pgd_mapping(swapper_pg_dir, FIXADDR_START,
> __pa_symbol(fixmap_pgd_next),
> PGDIR_SIZE, PAGE_TABLE);
> --
> 2.37.2
>
>
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