linux-kernel - Re: [PATCH 1/1] ARM: LPAE: use phys_addr_t instead of unsigned long in outercache hooks

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Date:   Sat, 26 Dec 2020 12:13:46 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        Jason Cooper <jason@...edaemon.net>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] ARM: LPAE: use phys_addr_t instead of unsigned long
 in outercache hooks

On Fri, Dec 25, 2020 at 07:44:58PM +0800, Zhen Lei wrote:
> The outercache of some Hisilicon SOCs support physical addresses wider
> than 32-bits. The unsigned long datatype is not sufficient for mapping
> physical addresses >= 4GB. The commit ad6b9c9d78b9 ("ARM: 6671/1: LPAE:
> use phys_addr_t instead of unsigned long in outercache functions") has
> already modified the outercache functions. But the parameters of the
> outercache hooks are not changed. This patch use phys_addr_t instead of
> unsigned long in outercache hooks: inv_range, clean_range, flush_range.
> 
> To ensure the outercache that does not support LPAE works properly, do
> cast phys_addr_t to unsigned long by adding a middle-tier function.

Please don't do that. The cast can be done inside the L2 functions
themselves without needing all these additional functions.

We probably ought to also add some protection against addresses > 4GB,
although these are hot paths, so we don't want to add tests in these
functions. Maybe instead checking whether the system has memory above
4GB while the L2 cache is being initialised would be a good idea?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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