linux-kernel - Re: 2.6.34 rex64 sysret instruction setup not preserving flags (r11 contents and eflags do not match)

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Message-ID: <AANLkTilUHCqbHB0YA5swqhzixXNW3gFpiTcl0z_5lOBe@mail.gmail.com>
Date:	Fri, 2 Jul 2010 22:58:52 -0600
From:	Jeffrey Merkey <jeffmerkey@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: 2.6.34 rex64 sysret instruction setup not preserving flags (r11 
	contents and eflags do not match)

On Fri, Jul 2, 2010 at 4:18 PM, Jeffrey Merkey <jeffmerkey@...il.com> wrote:
> On an AMD64 based system executing int 1 exceptions across a rex64
> sysret, if the debugger sets the trap flag, r11 which holds the eflags
> values for the
> sysret return from syscall, the flags do not appear to get set
> resutling in the int exception nesting by calling sysret over and over
> again until the kernel stack
> runs off the end.  Looks like the resume did not get set on this instruction.
>
> sysret on AMD requires the flags be saved into r11 and what I am
> seeing is the flags not matching what has been set in the pt_regs
> struct.
>
> Jeff
>

For some reason, zeroing the DR6 register before calling notify_die
makes this problem go away.

Jeff
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