linux-kernel - Re: [GIT PULL] x86/uapi for 3.8

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Message-Id: <50CF4FC502000078000B0CB6@nat28.tlf.novell.com>
Date:	Mon, 17 Dec 2012 16:00:53 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:	"Arnd Bergmann" <arnd@...db.de>, "Ingo Molnar" <mingo@...e.hu>,
	"Michael Kerrisk" <mtk.manpages@...il.com>,
	"Guennadi Liakhovetski" <g.liakhovetski@....de>,
	"Matt Fleming" <matt.fleming@...el.com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Dave Jones" <davej@...hat.com>,
	"David Howells" <dhowells@...hat.com>,
	"Grant Likely" <grant.likely@...retlab.ca>,
	"Markus Trippelsdorf" <markus@...ppelsdorf.de>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] x86/uapi for 3.8

>>> On 17.12.12 at 16:44, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Mon, Dec 17, 2012 at 1:04 AM, Jan Beulich <JBeulich@...e.com> wrote:
>>
>> How about this being caused by using the same lower level
>> page table entries that swapper_pg_dir uses, namely including
>> the _PAGE_GLOBAL bits? efi_call_virt_{pre,epi}log() only write
>> CR3 (see 185034e72d591f9465e5e18f937ed642e7ea0070), but
>> would need to also flip CR4.PGE afaict.
> 
> Now *this* is the kind of issue that I could easily see causing major
> corruption, but be subtle enough to not happen reliably. Coming back
> from the EFI calls (or going into them) with stale TLB contents due to
> global pages could explain things.
> 
> Good thinking. That efi call code should use flush_tlb_kernel() (or
> __flush_tlb_global() if it wants to avoid any paravirtualization
> stuff) if it has global pages in different places from the normal
> kernel map. Does it really have that?

I don't see it having such. But I also don't think flush_tlb_kernel()
is the right mechanism here. I'd rather suggest clearing CR4.PGE in
the "prelog", an restore it in the epilog. Para-virtual environments
shouldn't be directly interfacing with EFI runtime code anyway.

Jan

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