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From: Kamalesh Babulal <>
To: Joe Lawrence <>,
	Josh Poimboeuf <>,
	Peter Zijlstra <>,
	Randy Dunlap <>
Subject: Re: [PATCH] Revert "kbuild: use -flive-patching when CONFIG_LIVEPATCH is enabled"
Date: Mon, 20 Jul 2020 14:20:35 +0530	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 20/07/20 9:05 am, Joe Lawrence wrote:
> On 7/17/20 2:29 PM, Josh Poimboeuf wrote:
>> Use of the new -flive-patching flag was introduced with the following
>> commit:
>>    43bd3a95c98e ("kbuild: use -flive-patching when CONFIG_LIVEPATCH is enabled")
>> This flag has several drawbacks:
>> [ ... snip ... ]
>> - While there *is* a distro which relies on this flag for their distro
>>    livepatch module builds, there's not a publicly documented way to
>>    create safe livepatch modules with it.  Its use seems to be based on
>>    tribal knowledge.  It serves no benefit to those who don't know how to
>>    use it.
>>    (In fact, I believe the current livepatch documentation and samples
>>    are misleading and dangerous, and should be corrected.  Or at least
>>    amended with a disclaimer.  But I don't feel qualified to make such
>>    changes.)
> FWIW, I'm not exactly qualified to document source-based creation either, however I have written a few of the samples and obviously the kselftest modules.
> The samples should certainly include a disclaimer (ie, they are only for API demonstration purposes!) and eventually it would be great if the kselftest modules could guarantee their safety as well.  I don't know quite yet how we can automate that, but perhaps some kind of post-build sanity check could verify that they are in fact patching what they intend to patch.
> As for a more general, long-form warning about optimizations, I grabbed Miroslav's LPC slides from a few years back and poked around at some IPA-optimized disassembly... Here are my notes that attempt to capture some common cases:

Hi Joe,

The notes link you shared is not accessible.



  reply	other threads:[~2020-07-20  8:51 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 18:29 [PATCH] Revert "kbuild: use -flive-patching when CONFIG_LIVEPATCH is enabled" Josh Poimboeuf
2020-07-20  3:35 ` Joe Lawrence
2020-07-20  8:50   ` Kamalesh Babulal [this message]
2020-07-20 11:47     ` Joe Lawrence
2020-07-21 11:27   ` Miroslav Benes
2020-07-21 11:17 ` Miroslav Benes
2020-08-06  9:24   ` Petr Mladek
2020-09-01 17:24     ` Josh Poimboeuf
2020-09-03 10:02       ` Petr Mladek

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