Re: [Xen-devel] [PATCH v5 15/28] xsplice: Add .xsplice.hooks functions and test-case

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.04.16 at 10:23, <ross.lagerwall@xxxxxxxxxx> wrote:
> On 04/08/2016 06:39 PM, Jan Beulich wrote:
>>>>> On 08.04.16 at 17:57, <ross.lagerwall@xxxxxxxxxx> wrote:
>>> I've marked the following XSAs as potentially requiring hook functions
>>> or shadow variables:
>>>
>>> XSA-36

Again an example that I don't think can be live patched: The ACPI
tables the parsing of which gets adjusted may not be available
anymore at the time of patching.

>>> XSA-45

Hmm, this one is adding a field to struct vcpu, which by itself
already makes it very difficult to deal with this correctly in a
patch. But yes, to construct such a beast (if that's possible at
all), I can see how either or both of the above could be useful
here.

>>> XSA-60

While the field additions could be dealt with here, this again is
so complex a change that I personally wouldn't dare to
recommend using a live patch for this, even if someone managed
to create one.

>>> XSA-64

I don't think this can be fixed for any guests already started, as
it doesn't look like simply going and zapping the mis-initialized L4
entries would actually be correct in all cases.

>>> XSA-97

A field addition to an existing structure again - see above.

>>> XSA-107

Yes, this indeed could be dealt with in a hook (but I can also see
ways to deal with this without).

>>> XSA-114

Hmm, yes, if you really manage to enumerate all r/w locks in
the system, this could be dealt with in a hook too.

>>> XSA-150

Growing a structure again, so see above.

Overall I think that all of the cited examples are such which already
don't really lend themselves to live patching. Hence I think we're
going to be fine without these extra two pieces for the initial round,
taking into consideration just those cases where live patching is
reasonable to do.

Jan


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