linux-kernel - Re: [PATCH] n_tty: use kmalloc() instead of vmalloc() to avoid crash on armada-xp

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Date:	Wed, 11 Mar 2015 20:26:53 +0300
From:	Stas Sergeev <stsp@...t.ru>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
CC:	Linux kernel <linux-kernel@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org,
	Gregory Clément 
	<gregory.clement@...e-electrons.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>
Subject: Re: [PATCH] n_tty: use kmalloc() instead of vmalloc() to avoid crash
 on armada-xp

11.03.2015 19:52, Thomas Petazzoni пишет:
> Dear Stas Sergeev,
> No, this is not the right fix. The right fix is to upgrade your
> bootloader to a non-buggy one.
>
> Basically, the problem is that the memory information passed by the
> bootloader to the kernel is not consistent with the MBus base address
> which is the limit between RAM (below the MBus base address) and I/O
> registers (above the MBus base address).
>
> The bootloader tells the kernel that the RAM up to 0xf0000000 is
> usable, but sets the MBus base address to 0xe0000000. So whenever the
> kernel accesses 0xe0000000 -> 0xf0000000, it crashes, because you're
> not hitting RAM but MBus windows (and there are most likely no MBus
> window mapped in this space).
>
> Since kmalloc() relies on the identity mapping, it happens to mainly
> use pages at the beginning of the physical memory, which are OK. But
> vmalloc() happens to start using pages at the end of the physical
> memory (which are not part of the identity mapping), so that's why
> you're seeing this on the first access to a vmalloc()ed area.
>
> This problem has already been reported to Marvell and they have fixed
> it in their U-Boot. Please upgrade your bootloader, since there is not
> much the kernel can do about this: the bootloader is simply lying to
> the kernel about the amount of memory that is accessible.
Hello Thomas, thanks for that info!

Is there a quick way to test that?
I used memmap=0x20000000$0xe0000000 but nothing changed...
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