linux-kernel - Re: [Xen-devel] [PATCH v3 00/11] xen: Initial kexec/kdump implementation

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Date:	Fri, 11 Jan 2013 15:22:35 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Daniel Kiper <daniel.kiper@...cle.com>
CC:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	Andrew Cooper <Andrew.Cooper3@...rix.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"jbeulich@...e.com" <jbeulich@...e.com>,
	"maxim.uvarov@...cle.com" <maxim.uvarov@...cle.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"vgoyal@...hat.com" <vgoyal@...hat.com>
Subject: Re: [Xen-devel] [PATCH v3 00/11] xen: Initial kexec/kdump implementation

On 11/01/13 13:22, Daniel Kiper wrote:
> On Thu, Jan 10, 2013 at 02:19:55PM +0000, David Vrabel wrote:
>> On 04/01/13 17:01, Daniel Kiper wrote:
>>> My .5 cents:
>>>   - We should focus on KEXEC_CMD_kexec_load and KEXEC_CMD_kexec_unload;
>>>     probably we should introduce KEXEC_CMD_kexec_load2 and KEXEC_CMD_kexec_unload2;
>>>     load should __LOAD__ kernel image and other things into hypervisor memory;
>>
>> Yes, but I don't see how we can easily support both ABIs easily.  I'd be
>> in favour of replacing the existing hypercalls and requiring updated
>> kexec tools in dom0 (this isn't that different to requiring the correct
>> libxc in dom0).
> 
> Why? Just define new strutures for new functions of kexec hypercall.
> That should suffice.

The current hypervisor ABI depends on an internal kernel ABI (i.e., the
ABI provided by relocate_kernel).  We do not want hypervisor internals
to be constrained by having to be compatible with kernel internals.

>>>   - Hmmm... Now I think that we should still use kexec syscall to load image
>>>     into Xen memory (with new KEXEC_CMD_kexec_load2) because it establishes
>>>     all things which are needed to call kdump if dom0 crashes; however,
>>>     I could be wrong...
>>
>> I don't think we need the kexec syscall.  The kernel can unconditionally
>> do the crash hypercall, which will return if the kdump kernel isn't
>> loaded and the kernel can fall back to the regular non-kexec panic.
> 
> No, please do not do that. When you call HYPERVISOR_kexec_op(KEXEC_CMD_kexec)
> system is completly shutdown. Return form HYPERVISOR_kexec_op(KEXEC_CMD_kexec)
> would require to restore some kernel functionalities. It maybe impossible
> in some cases. Additionally, it means that some changes should be made
> in generic kexec code path. As I know kexec maintainers are very reluctant
> to make such things.

Huh?  There only needs to be a call to a new hypervisor_crash_kexec()
function (which would then call the Xen specific crash hypercall) at the
very beginning of crash_kexec().  If this returns the normal
crash/shutdown path is done (which could even include a guest kexec!).

David
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