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From: "Jan Beulich" <JBeulich@suse.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: andrew.cooper3@citrix.com, xen-devel@lists.xenproject.org,
	ross.lagerwall@citrix.com
Subject: Re: [PATCH v5 1/4] livepatch/docs: Document .bss not being cleared, and .data potentially having changed values
Date: Tue, 13 Sep 2016 10:12:07 -0600	[thread overview]
Message-ID: <57D84177020000780010E7FC@prv-mh.provo.novell.com> (raw)
In-Reply-To: <20160913155919.GA3326@char.us.oracle.com>

>>> On 13.09.16 at 17:59, <konrad.wilk@oracle.com> wrote:
> On Mon, Sep 12, 2016 at 01:49:51AM -0600, Jan Beulich wrote:
>> >>> On 11.09.16 at 17:48, <konrad.wilk@oracle.com> wrote:
>> > --- a/docs/misc/livepatch.markdown
>> > +++ b/docs/misc/livepatch.markdown
>> > @@ -875,6 +875,12 @@ section and the new function will reference the new string in the new
>> >  
>> >  This is implemented in the Xen Project hypervisor.
>> >  
>> > +Note that the .bss section is only cleared when the ELF payload is uploaded.
>> > +Subsequent apply/revert/apply operation do no clear the .bss (or reset the
>> > +.data to what it was when loaded). Hence it is the responsibility of the
>> > +creator of the payload to reset these values to known good state if they
>> > +depend on them having certain values at apply/revert states.
>> 
>> Was it, as an alternative, considered to disallow re-applying a
>> reverted patch without re-uploading?
> 
> I was thinking about it but not exactly sure of the ramifications.
> 
> That is if you go this route - revert a patch - we could go the
> next step and just unload it. But that puts some question on how
> to schedule that without corruption - say we have payload A,B and we
> are replacing A,B with C. A,B should be reverted and unloaded..
> 
> That means some form of list .. Ugh.
> 
> We could do a simpler way (which is what I think inline with your
> suggestion). This does the trick (and needs to be split up obviously)
> and also handles the case where you only have .text changes (like
> for NOPs).

At least that draft patch looks reasonable at a first glance.

Jan


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  reply	other threads:[~2016-09-13 16:13 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-11 15:48 [PATCH v5] Livepatch fixes and general features for Xen 4.8 Konrad Rzeszutek Wilk
2016-09-11 15:48 ` [PATCH v5 1/4] livepatch/docs: Document .bss not being cleared, and .data potentially having changed values Konrad Rzeszutek Wilk
2016-09-12  7:49   ` Jan Beulich
2016-09-13 15:59     ` Konrad Rzeszutek Wilk
2016-09-13 16:12       ` Jan Beulich [this message]
2016-09-11 15:48 ` [PATCH v5 2/4] livepatch: Add limit of 2MB to payload .bss sections Konrad Rzeszutek Wilk
2016-09-12  7:56   ` Jan Beulich
2016-09-13 16:04   ` Ross Lagerwall
2016-09-11 15:48 ` [PATCH v5 3/4] livepatch: NOP if func->new_addr is zero Konrad Rzeszutek Wilk
2016-09-12  8:04   ` Jan Beulich
2016-09-11 15:48 ` [PATCH v5 4/4] livepach: Add .livepatch.hooks functions and test-case Konrad Rzeszutek Wilk

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