linux-kernel - Re: [PATCH] MIPS: BMIPS: Reserve exception base to prevent corruption

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Date:   Wed, 3 Mar 2021 10:41:34 +0100
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-mips@...r.kernel.org, rppt@...nel.org,
        fancer.lancer@...il.com, guro@...com, akpm@...ux-foundation.org,
        paul@...pouillou.net,
        Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Kamal Dasu <kdasu.kdev@...il.com>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>,
        "open list:BROADCOM BMIPS MIPS ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] MIPS: BMIPS: Reserve exception base to prevent corruption

On Tue, Mar 02, 2021 at 05:30:18PM -0800, Florian Fainelli wrote:
> 
> 
> On 3/2/2021 3:54 PM, Thomas Bogendoerfer wrote:
> > On Mon, Mar 01, 2021 at 08:19:38PM -0800, Florian Fainelli wrote:
> >> BMIPS is one of the few platforms that do change the exception base.
> >> After commit 2dcb39645441 ("memblock: do not start bottom-up allocations
> >> with kernel_end") we started seeing BMIPS boards fail to boot with the
> >> built-in FDT being corrupted.
> >>
> >> Before the cited commit, early allocations would be in the [kernel_end,
> >> RAM_END] range, but after commit they would be within [RAM_START +
> >> PAGE_SIZE, RAM_END].
> >>
> >> The custom exception base handler that is installed by
> >> bmips_ebase_setup() done for BMIPS5000 CPUs ends-up trampling on the
> >> memory region allocated by unflatten_and_copy_device_tree() thus
> >> corrupting the FDT used by the kernel.
> >>
> >> To fix this, we need to perform an early reservation of the custom
> >> exception that is going to be installed and this needs to happen at
> >> plat_mem_setup() time to ensure that unflatten_and_copy_device_tree()
> >> finds a space that is suitable, away from reserved memory.
> >>
> >> Huge thanks to Serget for analysing and proposing a solution to this
> >> issue.
> >>
> >> Fixes: Fixes: 2dcb39645441 ("memblock: do not start bottom-up allocations with kernel_end")
> >> Debugged-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> >> Reported-by: Kamal Dasu <kdasu.kdev@...il.com>
> >> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> >> ---
> >> Thomas,
> >>
> >> This is intended as a stop-gap solution for 5.12-rc1 and to be picked up
> >> by the stable team for 5.11. We should find a safer way to avoid these
> >> problems for 5.13 maybe.
> > 
> > let's try to make it in one ago. Hwo about reserving vector space in
> > cpu_probe, if it's known there and leave the rest to trap_init() ?
> > 
> > Below patch got a quick test on IP22 (real hardware) and malta (qemu).
> > Not sure, if I got all BMIPS parts correct, so please check/test.
> 
> Works for me here:

perfect, I only forgot about R3k... I'll submit a formal patch submission
later today.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]