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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Miroslav Benes <mbenes@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>,
	David Laight <David.Laight@aculab.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Bill Wendling <morbo@google.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"mark.rutland@arm.com" <mark.rutland@arm.com>,
	"dvyukov@google.com" <dvyukov@google.com>,
	"seanjc@google.com" <seanjc@google.com>,
	"pbonzini@redhat.com" <pbonzini@redhat.com>,
	"llvm@lists.linux.dev" <llvm@lists.linux.dev>,
	"linux-toolchains@vger.kernel.org"
	<linux-toolchains@vger.kernel.org>,
	live-patching@vger.kernel.org
Subject: Re: [PATCH 20/22] x86,word-at-a-time: Remove .fixup usage
Date: Tue, 16 Nov 2021 13:27:45 -0800	[thread overview]
Message-ID: <20211115230737.27gqnzwvkaxoi7es@treble> (raw)
In-Reply-To: <alpine.LSU.2.21.2111151353550.29981@pobox.suse.cz>

On Mon, Nov 15, 2021 at 01:59:36PM +0100, Miroslav Benes wrote:
> On Fri, 12 Nov 2021, Josh Poimboeuf wrote:
> 
> > If the child schedules out, and then the parent gets patched, things can
> > go off-script if the child later jumps back to the unpatched version of
> > the parent, and then for example the old parent tries to call another
> > patched function with a since-changed ABI.
> 
> ...
>  
> > I don't know about other patch creation tooling, but I'd imagine they
> > also need to know about .cold functions, unless they have that
> > optimization disabled.  Because the func and its .cold counterpart
> > always need to be patched together.
> 
> We, at SUSE, solve the issue differently... the new patched parent would 
> call that another patched function with a changed ABI statically in a live 
> patch. So in that example, .cold child would jump back to the unpatched 
> parent which would then call, also, the unpatched function.

So if I understand correctly, if a function's ABI changes then you don't
patch it directly, but only patch its callers to call the replacement?

Is there a reason for that?

-- 
Josh


  reply	other threads:[~2021-11-16 21:27 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-05 17:10 [PATCH 00/22] x86: Remove anonymous out-of-line fixups Peter Zijlstra
2021-11-05 17:10 ` [PATCH 01/22] bitfield.h: Fix "type of reg too small for mask" test Peter Zijlstra
2021-11-05 17:10 ` [PATCH 02/22] x86,mmx_32: Remove .fixup usage Peter Zijlstra
2021-11-05 17:10 ` [PATCH 03/22] x86,copy_user_64: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 04/22] x86,copy_mc_64: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 05/22] x86,entry_64: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 06/22] x86,entry_32: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 07/22] x86,extable: Extend extable functionality Peter Zijlstra
2021-11-05 17:10 ` [PATCH 08/22] x86,msr: Remove .fixup usage Peter Zijlstra
2021-11-05 17:10 ` [PATCH 09/22] x86,futex: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 10/22] x86,uaccess: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 11/22] x86,xen: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 12/22] x86,fpu: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 13/22] x86,segment: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 14/22] x86,vmx: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 15/22] x86,checksum_32: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 16/22] x86,sgx: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 17/22] x86,kvm: " Peter Zijlstra
2021-11-05 17:10 ` [PATCH 18/22] x86,usercopy_32: Simplify __copy_user_intel_nocache() Peter Zijlstra
2021-11-05 17:10 ` [PATCH 19/22] x86,usercopy: Remove .fixup usage Peter Zijlstra
2021-11-05 17:10 ` [PATCH 20/22] x86,word-at-a-time: " Peter Zijlstra
2021-11-05 18:01   ` Josh Poimboeuf
2021-11-05 18:07     ` Peter Zijlstra
2021-11-08 16:47   ` Josh Poimboeuf
2021-11-08 18:29     ` Peter Zijlstra
2021-11-08 18:53       ` Nick Desaulniers
2021-11-09  8:23         ` Peter Zijlstra
2021-11-09 19:22           ` Nick Desaulniers
2021-11-09 20:59             ` Bill Wendling
2021-11-09 21:21               ` Peter Zijlstra
2021-11-09 21:25                 ` Nick Desaulniers
2021-11-09 22:11                   ` Peter Zijlstra
2021-11-09 22:15                     ` Nick Desaulniers
2021-11-09 21:07             ` Peter Zijlstra
2021-11-10 10:18               ` Peter Zijlstra
2021-11-10 10:46               ` David Laight
2021-11-10 11:09                 ` Peter Zijlstra
2021-11-10 12:20                   ` David Laight
2021-11-12  1:50                     ` Josh Poimboeuf
2021-11-12  9:33                       ` Peter Zijlstra
2021-11-13  5:35                         ` Josh Poimboeuf
2021-11-15 12:36                           ` Miroslav Benes
2021-11-15 13:01                             ` Joe Lawrence
2021-11-15 23:40                               ` Josh Poimboeuf
2021-11-16  7:25                                 ` Miroslav Benes
2021-11-15 12:59                           ` Miroslav Benes
2021-11-16 21:27                             ` Josh Poimboeuf [this message]
2021-11-18  7:15                               ` Miroslav Benes
2021-11-22 17:46                       ` Petr Mladek
2021-11-24 17:42                         ` Josh Poimboeuf
2021-11-25  8:18                           ` Petr Mladek
2021-11-10 12:14               ` Segher Boessenkool
2021-11-05 17:10 ` [PATCH 21/22] x86: Remove .fixup section Peter Zijlstra
2021-11-05 17:10 ` [PATCH 22/22] objtool: Remove .fixup handling Peter Zijlstra

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