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Date: Mon, 25 Mar 2024 21:40:41 +0100
From: "Arnd Bergmann" <arnd@arndb.de>
To: "Samuel Holland" <samuel.holland@sifive.com>,
 "Palmer Dabbelt" <palmer@dabbelt.com>, linux-riscv@lists.infradead.org
Cc: "Albert Ou" <aou@eecs.berkeley.edu>,
 "Alexandre Ghiti" <alexghiti@rivosinc.com>,
 "Andrew Morton" <akpm@linux-foundation.org>,
 "Charlie Jenkins" <charlie@rivosinc.com>, guoren <guoren@kernel.org>,
 "Jisheng Zhang" <jszhang@kernel.org>,
 "Kemeng Shi" <shikemeng@huaweicloud.com>,
 "Matthew Wilcox" <willy@infradead.org>, "Mike Rapoport" <rppt@kernel.org>,
 "Paul Walmsley" <paul.walmsley@sifive.com>,
 "Xiao W Wang" <xiao.w.wang@intel.com>, "Yangyu Chen" <cyy@cyyself.name>,
 linux-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: Define TASK_SIZE_MAX for __access_ok()
Content-Type: text/plain

On Wed, Mar 13, 2024, at 18:59, Samuel Holland wrote:
> TASK_SIZE_MAX should be set to the largest userspace address under any
> runtime configuration. This optimizes the check in __access_ok(), which
> no longer needs to compute the current value of TASK_SIZE. It is still
> safe because addresses between TASK_SIZE and TASK_SIZE_MAX are invalid
> at the hardware level.
>
> This removes about half of the references to pgtable_l[45]_enabled.
>
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>

Reviewed-by: Arnd Bergmann <arnd@arndb.de>

>  #ifdef CONFIG_64BIT
>  #define TASK_SIZE_64	(PGDIR_SIZE * PTRS_PER_PGD / 2)
>  #define TASK_SIZE_MIN	(PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
> +#define TASK_SIZE_MAX	(PGDIR_SIZE_L5 * PTRS_PER_PGD / 2)

I see that TASK_SIZE_MIN is unused since 085e2ff9aeb0 ("efi:
libstub: Drop randomization of runtime memory map") and could
be dropped now, but it doesn't really hurt either.

     Arnd