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Re: [PATCH] x86/asm: ELF metadata for simple cases
- To: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Fri, 24 Feb 2023 16:34:57 +0000
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- Cc: Jan Beulich <JBeulich@xxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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On 20/02/2023 11:51 am, Ross Lagerwall wrote:
>> From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> Sent: Monday, February 20, 2023 11:04 AM
>> To: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
>> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Jan Beulich
>> <JBeulich@xxxxxxxx>; Roger Pau Monne <roger.pau@xxxxxxxxxx>; Wei Liu
>> <wl@xxxxxxx>; Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>; Ross Lagerwall
>> <ross.lagerwall@xxxxxxxxxx>
>> Subject: [PATCH] x86/asm: ELF metadata for simple cases
>>
>> This is generally good practice, and necessary for livepatch binary diffing
>> to
>> work.
>>
>> With this, livepatching of the SVM entry path works. The only complication
>> is
>> with svm_stgi_label which is only used by oprofile to guestimate (not
>> completely correctly) when an NMI hit guest context.
>>
>> Livepatching of VMX is still an open question, because the logic doesn't form
>> anything remotely resembling functions. Both code fragments jump into each
>> other so need to be updated in tandem. Also, both code fragment entries need
>> trampolines in the case that patching actually occurs. For now, just treat
>> it
>> as a single function.
> If it is treated as two functions and both functions are always included in
> the live patch, would that work?
I think so, but only because the first jumped-to label in
vmx_asm_do_vmentry is beyond the trampoline.
But I guess the question is how to tie the two symbols together. We
don't want to be hardcoding this in livepatch-build-tools IMO.
Perhaps we want a CONFIG_LIVEPATCH build of Xen to include a
section/note/something identifying "grouped symbols", meaning "if
there's a delta in one, include all even if they haven't changed" ?
I'm getting the distinct impression that we're going to need it it for
the PV entry/exit paths too.
~Andrew
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