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Date:   Mon, 27 Mar 2023 11:37:28 +0100
From:   Conor Dooley <conor.dooley@microchip.com>
To:     Alexandre Ghiti <alexghiti@rivosinc.com>
CC:     Jonathan Corbet <corbet@lwn.net>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>, <linux-doc@vger.kernel.org>,
        <linux-riscv@lists.infradead.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH -fixes 1/2] riscv: Move early dtb mapping into the fixmap
 region
Message-ID: <292617ac-b63b-473d-8d4e-2817d17233a1@spud>
References: <20230323163347.182895-1-alexghiti@rivosinc.com>
 <20230323163347.182895-2-alexghiti@rivosinc.com>
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Hey Alex!

On Thu, Mar 23, 2023 at 05:33:46PM +0100, Alexandre Ghiti wrote:
> riscv establishes 2 virtual mappings:
>=20
> - early_pg_dir maps the kernel which allows to discover the system
>   memory
> - swapper_pg_dir installs the final mapping (linear mapping included)
>=20
> 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.
>=20
> 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@microchip.com>
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@microchip.com>

> Reported-by: Conor Dooley <Conor.Dooley@microchip.com>

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@mi=
crochip.com/
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> ---
>  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(-)
>=20
> diff --git a/Documentation/riscv/vm-layout.rst b/Documentation/riscv/vm-l=
ayout.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-s=
pace 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-s=
pace 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-s=
pace 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/fix=
map.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 =3D 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/pg=
table.h
> index ab05f892d317..f641837ccf31 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -87,9 +87,13 @@
> =20
>  #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)
> =20
> 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();
> =20
>  	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(unsign=
ed long)]
>  EXPORT_SYMBOL(empty_zero_page);
> =20
>  extern char _start[];
> -#define DTB_EARLY_BASE_VA      PGDIR_SIZE
>  void *_dtb_early_va __initdata;
>  uintptr_t _dtb_early_pa __initdata;
> =20
> @@ -236,6 +235,14 @@ static void __init setup_bootmem(void)
>  	set_max_mapnr(max_low_pfn - ARCH_PFN_OFFSET);
> =20
>  	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;
> =20
>  pgd_t early_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
> -static p4d_t __maybe_unused early_dtb_p4d[PTRS_PER_P4D] __initdata __ali=
gned(PAGE_SIZE);
> -static pud_t __maybe_unused early_dtb_pud[PTRS_PER_PUD] __initdata __ali=
gned(PAGE_SIZE);
> -static pmd_t __maybe_unused early_dtb_pmd[PTRS_PER_PMD] __initdata __ali=
gned(PAGE_SIZE);
> =20
>  #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 PG=
DIR
>   * entry.
>   */
> -static void __init create_fdt_early_page_table(pgd_t *pgdir, uintptr_t d=
tb_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 =3D dtb_pa & ~(PMD_SIZE - 1);
> =20
> -	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));
> =20
> -	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);
>  	}
> =20
> -	dtb_early_va =3D (void *)DTB_EARLY_BASE_VA + (dtb_pa & (PMD_SIZE - 1));
> +	dtb_early_va =3D (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);
> =20
>  	/* 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);
> =20
>  	/*
>  	 * Bootime fixmap only can handle PMD_SIZE mapping. Thus, boot-ioremap
> @@ -1097,6 +1094,16 @@ static void __init setup_vm_final(void)
>  	u64 i;
> =20
>  	/* 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 =3D 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);
> --=20
> 2.37.2
>=20
>=20

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