From: Miroslav Benes <mbenes@suse.cz>
To: Josh Poimboeuf <jpoimboe@redhat.com>
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, nstange@suse.de
Subject: Re: [PATCH 20/22] x86,word-at-a-time: Remove .fixup usage
Date: Thu, 18 Nov 2021 08:15:23 +0100 (CET) [thread overview]
Message-ID: <alpine.LSU.2.21.2111180811370.16632@pobox.suse.cz> (raw)
In-Reply-To: <20211115230737.27gqnzwvkaxoi7es@treble>
On Tue, 16 Nov 2021, Josh Poimboeuf wrote:
> 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?
Yes.
> Is there a reason for that?
Not really. There were a couple of cases in the past where this was safer
to implement and then it became a habbit, I guess.
[ Nicolai CCed, if he wants to add more details ]
Miroslav
next prev parent reply other threads:[~2021-11-18 7:15 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
2021-11-18 7:15 ` Miroslav Benes [this message]
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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