linux-kernel - Re: [PATCH v2] riscv: Extend sv39 linear mapping max size to 128G

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Message-ID: <CAHVXubg+aXS7-smmWS9LwUbAkpfGvet9Zk0UJs_AZhxV2vx6UQ@mail.gmail.com>
Date: Mon, 1 Jul 2024 13:58:27 +0200
From: Alexandre Ghiti <alexghiti@...osinc.com>
To: Stuart Menefy <stuart.menefy@...asip.com>
Cc: Jonathan Corbet <corbet@....net>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, linux-doc@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] riscv: Extend sv39 linear mapping max size to 128G

Hi Stuart,

On Sun, Jun 30, 2024 at 1:06 PM Stuart Menefy <stuart.menefy@...asip.com> wrote:
>
> This harmonizes all virtual addressing modes which can now all map
> (PGDIR_SIZE * PTRS_PER_PGD) / 4 of physical memory.
>
> The RISCV implementation of KASAN requires that the boundary between
> shallow mappings are aligned on an 8G boundary. In this case we need
> VMALLOC_START to be 8G aligned. So although we only need to move the
> start of the linear mapping down by 4GiB to allow 128GiB to be mapped,
> we actually move it down by 8GiB (creating a 4GiB hole between the
> linear mapping and KASAN shadow space) to maintain the alignment
> requirement.
>
> Signed-off-by: Stuart Menefy <stuart.menefy@...asip.com>
> ---
>
> Changes since V1:
> This is a modified version of the patch posted by Alexandre Ghiti
> <alexghiti@...osinc.com> [1]. That version moved the start of the
> liner mapping by 4GiB, but was subsequently found to trigger a problem
> in the KASAN code [2]. By moving the start address by 8GiB alignment
> requiremenents are maintained.
>
> [1] https://lore.kernel.org/linux-riscv/20240514133614.87813-1-alexghiti@rivosinc.com/
> [2] https://lore.kernel.org/linux-riscv/4011b34a-1b86-42c7-aaf6-3bd297149f06@ghiti.fr/
>
> ---
>  Documentation/arch/riscv/vm-layout.rst | 11 ++++++-----
>  arch/riscv/include/asm/page.h          |  2 +-
>  2 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/arch/riscv/vm-layout.rst b/Documentation/arch/riscv/vm-layout.rst
> index e476b4386bd9..077b968dcc81 100644
> --- a/Documentation/arch/riscv/vm-layout.rst
> +++ b/Documentation/arch/riscv/vm-layout.rst
> @@ -47,11 +47,12 @@ RISC-V Linux Kernel SV39
>                                                                | Kernel-space virtual memory, shared between all processes:
>    ____________________________________________________________|___________________________________________________________
>                      |            |                  |         |
> -   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
> -   ffffffd800000000 | -160    GB | fffffff6ffffffff |  124 GB | direct mapping of all physical memory
> +   ffffffc4fea00000 | -236    GB | ffffffc4feffffff |    6 MB | fixmap
> +   ffffffc4ff000000 | -236    GB | ffffffc4ffffffff |   16 MB | PCI io
> +   ffffffc500000000 | -236    GB | ffffffc5ffffffff |    4 GB | vmemmap
> +   ffffffc600000000 | -232    GB | ffffffd5ffffffff |   64 GB | vmalloc/ioremap space
> +   ffffffd600000000 | -168    GB | fffffff5ffffffff |  128 GB | direct mapping of all physical memory
> +                    |            |                  |         |
>     fffffff700000000 |  -36    GB | fffffffeffffffff |   32 GB | kasan
>    __________________|____________|__________________|_________|____________________________________________________________
>                                                                |
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 115ac98b8d72..81d47fbbd927 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -37,7 +37,7 @@
>   * define the PAGE_OFFSET value for SV48 and SV39.
>   */
>  #define PAGE_OFFSET_L4         _AC(0xffffaf8000000000, UL)
> -#define PAGE_OFFSET_L3         _AC(0xffffffd800000000, UL)
> +#define PAGE_OFFSET_L3         _AC(0xffffffd600000000, UL)
>  #else
>  #define PAGE_OFFSET            _AC(CONFIG_PAGE_OFFSET, UL)
>  #endif /* CONFIG_64BIT */
> --
> 2.43.0
>

So the issue was with my patch, sorry! Your fix makes sense so you can add:

Reviewed-by: Alexandre Ghiti <alexghiti@...osinc.com>

Thanks,

Alex