linux-kernel - Re: [PATCH 1/3] loongarch: Wire up 32 bit syscalls

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Message-Id: <03b0d959-9a25-4a67-bd66-979fd6909430@app.fastmail.com>
Date: Sat, 04 Jan 2025 16:31:18 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Jiaxun Yang" <jiaxun.yang@...goat.com>,
 "Huacai Chen" <chenhuacai@...nel.org>, "WANG Xuerui" <kernel@...0n.name>
Cc: loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH 1/3] loongarch: Wire up 32 bit syscalls

On Thu, Jan 2, 2025, at 19:34, Jiaxun Yang wrote:
> 
> +#ifdef CONFIG_32BIT
> +SYSCALL_DEFINE6(mmap2, unsigned long, addr, unsigned long, len, unsigned long,
> +		prot, unsigned long, flags, unsigned long, fd, unsigned long, offset)
> +{
> +	/*
> +	 * Note that the shift for mmap2 is constant (12),
> +	 * regardless of PAGE_SIZE
> +	 */
> +
> +	if (offset & (~PAGE_MASK >> 12))
> +		return -EINVAL;
> +
> +	return ksys_mmap_pgoff(addr, len, prot, flags, fd,
> +			       offset >> (PAGE_SHIFT - 12));
> +}
> +#endif

I think it's time we move this into mm/mmap.c and agree on the calling
conventions across architectures. I'm currently travelling, but I can
dig out a patch I made a while ago to convert most 32-bit
architectures over to a common mmap2() implementation.

As far as I can tell, the only architectures that actually want
mmap_pgoff() are m68k, arc and hexagon. Everything else either has
a fixed 4KB page size (so mmap_pgoff and mmap2 are the same), or
they already enforce the mmap2 semantics.

There are some smaller differences between architectures at the
moment that I think shouldn't really exist: sparc32/m68k/arm32/parisc
skips the alignment check, sparc64 and alpha add an overflow check (on
sys_mmap) and powerpc adds a pgprot argument check. I think the
version you have is fine for common code (including the ones that
don't check alignment today), not sure about the additional checks.

     Arnd