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From: Thomas Gleixner <tglx@linutronix.de>
To: William Grant <william.grant@canonical.com>
Cc: Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86: Fix overlap of i386 CPU_ENTRY_AREA with FIX_BTMAP
Date: Tue, 30 Jan 2018 14:10:20 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.20.1801301409430.1797@nanos> (raw)
In-Reply-To: <7041d181-a019-e8b9-4e4e-48215f841e2c@canonical.com>

On Tue, 30 Jan 2018, William Grant wrote:

> Since commit 92a0f81d8957 ("x86/cpu_entry_area: Move it out of the
> fixmap"), i386's CPU_ENTRY_AREA has been mapped to the memory area just
> below FIXADDR_START. But already immediately before FIXADDR_START is the
> FIX_BTMAP area, which means that early_ioremap can collide with the
> entry area.
> 
> It's especially bad on PAE where FIX_BTMAP_BEGIN gets aligned to exactly
> match CPU_ENTRY_AREA_BASE, so the first early_ioremap slot clobbers the
> IDT and causes interrupts during early boot to reset the system.
> 
> The overlap wasn't a problem before the CPU entry area was introduced,
> as the fixmap has classically been preceded by the pkmap or vmalloc
> areas, neither of which is used until early_ioremap is out of the
> picture.
> 
> Relocate CPU_ENTRY_AREA to below FIX_BTMAP, not just below the permanent
> fixmap area.

Nice catch. I'm sure I stared at that more than once....

Thanks,

	tglx

  reply	other threads:[~2018-01-30 13:10 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-30 11:22 William Grant
2018-01-30 13:10 ` Thomas Gleixner [this message]
2018-01-30 14:48 ` [tip:x86/pti] x86/mm: " tip-bot for William Grant

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