From: ebiederm@xmission.com (Eric W. Biederman)
To: Daniel Kiper <daniel.kiper@oracle.com>
Cc: keir@xen.org, keescook@chromium.org, kexec@lists.infradead.org,
linux-kernel@vger.kernel.org, xen-devel@lists.xen.org,
hbabu@us.ibm.com, david.vrabel@citrix.com, jbeulich@suse.com,
hpa@linux.intel.com, vgoyal@redhat.com
Subject: Re: kexec: Clearing registers just before jumping into purgatory
Date: Fri, 11 Oct 2013 03:08:43 -0700 [thread overview]
Message-ID: <877gdkce6s.fsf@tw-ebiederman.twitter.com> (raw)
In-Reply-To: <20131011092837.GZ3626@debian70-amd64.local.net-space.pl> (Daniel Kiper's message of "Fri, 11 Oct 2013 11:28:37 +0200")
Daniel Kiper <daniel.kiper@oracle.com> writes:
> Hi,
>
> Could you explain why do you clear all registers just before jumping
> into purgatory (please look into arch/x86/kernel/relocate_kernel_64.S
> for more details)? There is no any single word about that. I do not
> count comment which states what is going on. purgatory on entry does
> not assume any value in registers. Are you going to use that feature
> for something in the future (e.g. to differentiate between callers
> and/or Linux versions if it be needed)?
It has been a long time now, but as I recall the reason was to just
have things well defined and to make certain that we were not
accidentially exporting anything except the stack pointer for
applications to depend upon.
0/NULL is a good choice because if you are expecting pointer for some
strange reason interesting things happen.
purgatory is definitely not the only target and the C version of
purgatory was actually written well after kexec came into existence.
Is there any particular reason why you are asking?
> By the way, interestingly it is not done if preserve_context is in
> force.
Something different is done, and all of the registers should be
preserved from the when the return to Linux.
In theory you can swap between to kernels with the preserve_context
case. Technically I like the ability but I don't know that it has ever
achieved much uptake.
Eric
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WARNING: multiple messages have this Message-ID (diff)
From: ebiederm@xmission.com (Eric W. Biederman)
To: Daniel Kiper <daniel.kiper@oracle.com>
Cc: hbabu@us.ibm.com, hpa@linux.intel.com, keescook@chromium.org,
vgoyal@redhat.com, kexec@lists.infradead.org,
linux-kernel@vger.kernel.org, david.vrabel@citrix.com,
jbeulich@suse.com, keir@xen.org, xen-devel@lists.xen.org
Subject: Re: kexec: Clearing registers just before jumping into purgatory
Date: Fri, 11 Oct 2013 03:08:43 -0700 [thread overview]
Message-ID: <877gdkce6s.fsf@tw-ebiederman.twitter.com> (raw)
In-Reply-To: <20131011092837.GZ3626@debian70-amd64.local.net-space.pl> (Daniel Kiper's message of "Fri, 11 Oct 2013 11:28:37 +0200")
Daniel Kiper <daniel.kiper@oracle.com> writes:
> Hi,
>
> Could you explain why do you clear all registers just before jumping
> into purgatory (please look into arch/x86/kernel/relocate_kernel_64.S
> for more details)? There is no any single word about that. I do not
> count comment which states what is going on. purgatory on entry does
> not assume any value in registers. Are you going to use that feature
> for something in the future (e.g. to differentiate between callers
> and/or Linux versions if it be needed)?
It has been a long time now, but as I recall the reason was to just
have things well defined and to make certain that we were not
accidentially exporting anything except the stack pointer for
applications to depend upon.
0/NULL is a good choice because if you are expecting pointer for some
strange reason interesting things happen.
purgatory is definitely not the only target and the C version of
purgatory was actually written well after kexec came into existence.
Is there any particular reason why you are asking?
> By the way, interestingly it is not done if preserve_context is in
> force.
Something different is done, and all of the registers should be
preserved from the when the return to Linux.
In theory you can swap between to kernels with the preserve_context
case. Technically I like the ability but I don't know that it has ever
achieved much uptake.
Eric
next prev parent reply other threads:[~2013-10-11 10:12 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-11 9:28 kexec: Clearing registers just before jumping into purgatory Daniel Kiper
2013-10-11 9:28 ` Daniel Kiper
2013-10-11 10:08 ` Eric W. Biederman [this message]
2013-10-11 10:08 ` Eric W. Biederman
2013-10-11 11:04 ` Daniel Kiper
2013-10-11 11:04 ` Daniel Kiper
2013-10-11 11:04 ` Daniel Kiper
2013-10-11 12:52 ` Vivek Goyal
2013-10-11 12:52 ` Vivek Goyal
2013-10-11 12:52 ` Vivek Goyal
2013-10-11 15:37 ` Matthew Garrett
2013-10-11 15:37 ` Matthew Garrett
2013-10-11 15:37 ` Matthew Garrett
2013-10-11 15:44 ` Vivek Goyal
2013-10-11 15:44 ` Vivek Goyal
2013-10-11 15:48 ` Matthew Garrett
2013-10-11 15:48 ` Matthew Garrett
2013-10-11 15:48 ` Matthew Garrett
2013-10-11 16:33 ` Richard Weinberger
2013-10-11 16:33 ` Richard Weinberger
2013-10-11 16:39 ` Matthew Garrett
2013-10-11 16:39 ` Matthew Garrett
2013-10-11 16:42 ` Richard Weinberger
2013-10-11 16:42 ` Richard Weinberger
2013-10-11 16:44 ` Matthew Garrett
2013-10-11 16:44 ` Matthew Garrett
2013-10-11 16:47 ` Richard Weinberger
2013-10-11 16:47 ` Richard Weinberger
2013-10-11 16:55 ` Matthew Garrett
2013-10-11 16:55 ` Matthew Garrett
2013-10-11 16:59 ` Richard Weinberger
2013-10-11 16:59 ` Richard Weinberger
2013-10-11 17:01 ` Matthew Garrett
2013-10-11 17:01 ` Matthew Garrett
2013-10-11 17:01 ` Matthew Garrett
2013-10-11 20:44 ` Eric W. Biederman
2013-10-11 20:44 ` Eric W. Biederman
2013-10-11 20:44 ` Eric W. Biederman
2013-10-11 20:50 ` Matthew Garrett
2013-10-11 20:50 ` Matthew Garrett
2013-10-11 20:50 ` Matthew Garrett
2013-10-11 16:59 ` Richard Weinberger
2013-10-11 16:55 ` Matthew Garrett
2013-10-11 16:47 ` Richard Weinberger
2013-10-11 16:53 ` Vivek Goyal
2013-10-11 16:53 ` Vivek Goyal
2013-10-11 16:56 ` Matthew Garrett
2013-10-11 16:56 ` Matthew Garrett
2013-10-11 16:56 ` Matthew Garrett
2013-10-11 16:53 ` Vivek Goyal
2013-10-11 16:44 ` Matthew Garrett
2013-10-11 16:42 ` Richard Weinberger
2013-10-11 16:39 ` Matthew Garrett
2013-10-11 16:33 ` Richard Weinberger
2013-10-11 15:44 ` Vivek Goyal
2013-10-11 22:15 ` Eric W. Biederman
2013-10-11 22:15 ` Eric W. Biederman
2013-10-14 18:24 ` Daniel Kiper
2013-10-14 18:24 ` Daniel Kiper
2013-10-14 18:24 ` Daniel Kiper
2013-10-11 22:15 ` Eric W. Biederman
2013-10-11 10:08 ` Eric W. Biederman
-- strict thread matches above, loose matches on Subject: below --
2013-10-11 9:28 Daniel Kiper
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