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From: Anup Patel <anup@brainfault.org>
To: Alexandre Ghiti <alex@ghiti.fr>
Cc: "linux-kernel@vger.kernel.org List"
	<linux-kernel@vger.kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>, Zong Li <zong.li@sifive.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [RFC PATCH 7/7] riscv: Explicit comment about user virtual address space size
Date: Thu, 26 Mar 2020 12:35:08 +0530
Message-ID: <CAAhSdy3kV6kVHM-sL2uFBgq85EOiKWRJrfNvd+MPiOjKQJwavQ@mail.gmail.com> (raw)
In-Reply-To: <20200322110028.18279-8-alex@ghiti.fr>

On Sun, Mar 22, 2020 at 4:37 PM Alexandre Ghiti <alex@ghiti.fr> wrote:
>
> Define precisely the size of the user accessible virtual space size
> for sv32/39/48 mmu types and explain why the whole virtual address
> space is split into 2 equal chunks between kernel and user space.
>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> ---
>  arch/riscv/include/asm/pgtable.h | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 06361db3f486..be117a0b4ea1 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -456,8 +456,15 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
>  #define FIXADDR_START    (FIXADDR_TOP - FIXADDR_SIZE)
>
>  /*
> - * Task size is 0x4000000000 for RV64 or 0x9fc00000 for RV32.
> - * Note that PGDIR_SIZE must evenly divide TASK_SIZE.
> + * Task size is:
> + * -     0x9fc00000 (~2.5GB) for RV32.
> + * -   0x4000000000 ( 256GB) for RV64 using SV39 mmu
> + * - 0x800000000000 ( 128TB) for RV64 using SV48 mmu
> + *
> + * Note that PGDIR_SIZE must evenly divide TASK_SIZE since "RISC-V
> + * Instruction Set Manual Volume II: Privileged Architecture" states that
> + * "load and store effective addresses, which are 64bits, must have bits
> + * 63–48 all equal to bit 47, or else a page-fault exception will occur."
>   */
>  #ifdef CONFIG_64BIT
>  #define TASK_SIZE (PGDIR_SIZE * PTRS_PER_PGD / 2)
> --
> 2.20.1
>

Looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup


  reply index

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-22 11:00 [RFC PATCH 0/7] Introduce sv48 support Alexandre Ghiti
2020-03-22 11:00 ` [RFC PATCH 1/7] riscv: Get rid of compile time logic with MAX_EARLY_MAPPING_SIZE Alexandre Ghiti
2020-03-26  6:10   ` Anup Patel
2020-04-03 15:17   ` Palmer Dabbelt
2020-03-22 11:00 ` [RFC PATCH 2/7] riscv: Allow to dynamically define VA_BITS Alexandre Ghiti
2020-03-26  6:12   ` Anup Patel
2020-04-03 15:17   ` Palmer Dabbelt
2020-03-22 11:00 ` [RFC PATCH 3/7] riscv: Simplify MAXPHYSMEM config Alexandre Ghiti
2020-03-26  6:22   ` Anup Patel
2020-03-26  6:34   ` Anup Patel
2020-04-03 15:53   ` Palmer Dabbelt
2020-03-22 11:00 ` [RFC PATCH 4/7] riscv: Implement sv48 support Alexandre Ghiti
2020-03-26  7:00   ` Anup Patel
2020-03-31 16:31     ` Alex Ghiti
2020-04-03 15:53   ` Palmer Dabbelt
2020-03-22 11:00 ` [RFC PATCH 5/7] riscv: Use pgtable_l4_enabled to output mmu type in cpuinfo Alexandre Ghiti
2020-03-26  7:01   ` Anup Patel
2020-04-03 15:53   ` Palmer Dabbelt
2020-03-22 11:00 ` [RFC PATCH 6/7] dt-bindings: riscv: Remove "riscv, svXX" property from device-tree Alexandre Ghiti
2020-03-26  7:03   ` Anup Patel
2020-04-03 15:53   ` Palmer Dabbelt
2020-03-22 11:00 ` [RFC PATCH 7/7] riscv: Explicit comment about user virtual address space size Alexandre Ghiti
2020-03-26  7:05   ` Anup Patel [this message]
2020-04-03 15:53   ` Palmer Dabbelt
2020-03-31 19:53 ` [RFC PATCH 0/7] Introduce sv48 support Palmer Dabbelt

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