Re: [Xen-devel] [PATCH v2 01/11] kexec: introduce kexec_ops struct

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 23/11/2012 01:38, H. Peter Anvin wrote:
> I still don't really get why it can't be isolated from dom0, which would make 
> more sense to me, even for a Xen crash.
>

The crash region (as specified by crashkernel= on the Xen command line)
is isolated from dom0.

dom0 (using the kexec utility etc) has the task of locating the Xen
crash notes (using the kexec hypercall interface), constructing a binary
blob containing kernel, initram and gubbins, and asking Xen to put this
blob in the crash region (again, using the kexec hypercall interface).

I do not see how this is very much different from the native case
currently (although please correct me if I am misinformed).  Linux has
extra work to do by populating /proc/iomem with the Xen crash regions
boot (so the kexec utility can reference their physical addresses when
constructing the blob), and should just act as a conduit between the
kexec system call and the kexec hypercall to load the blob.

For within-guest kexec/kdump functionality, I agree that it is barking
mad.  However, we do see cloud operators interested in the idea so VM
administrators can look after their crashes themselves.

~Andrew

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