From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 12F752C80 for ; Mon, 15 Nov 2021 13:07:40 +0000 (UTC) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 8934A21A5A; Mon, 15 Nov 2021 12:59:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1636981176; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dj+b9TzFtWSZEXv8wRzJx6fLOVSK62UITZzIdTTV6gw=; b=2gFpRabP9s8dsJnS1A7v4cHkznUF1SdkTtUcOQ0lJJbwsuqvh4FUCxYe/C48cChEfLt/fp TjfqJzw7hd+2aRD3d+ImhxW1YZhsjU7kAkYD6jCIGZBjjxjDIX4AdzpeCNgvg03+PaKDGN PPtoBxCVLw1kYohGX6DtsQFlij7cuLQ= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1636981176; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dj+b9TzFtWSZEXv8wRzJx6fLOVSK62UITZzIdTTV6gw=; b=YDPmQ2Ic8mYr1pHZxfbdF1zWOrBtnQNvOiC7mcIA9Y7GAfZahLjWprcjCIO0dldbQdJP4j 9ymTik0cLpBeSbBg== Received: from pobox.suse.cz (pobox.suse.cz [10.100.2.14]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 4697CA3B81; Mon, 15 Nov 2021 12:59:36 +0000 (UTC) Date: Mon, 15 Nov 2021 13:59:36 +0100 (CET) From: Miroslav Benes To: Josh Poimboeuf cc: Peter Zijlstra , David Laight , Nick Desaulniers , Bill Wendling , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , "mark.rutland@arm.com" , "dvyukov@google.com" , "seanjc@google.com" , "pbonzini@redhat.com" , "llvm@lists.linux.dev" , "linux-toolchains@vger.kernel.org" , live-patching@vger.kernel.org Subject: Re: [PATCH 20/22] x86,word-at-a-time: Remove .fixup usage In-Reply-To: <20211113053500.jcnx5airbn7g763a@treble> Message-ID: References: <20211109210736.GV174703@worktop.programming.kicks-ass.net> <2734a37ebed2432291345aaa8d9fd47e@AcuMS.aculab.com> <20211112015003.pefl656m3zmir6ov@treble> <20211113053500.jcnx5airbn7g763a@treble> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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. The situation would change if we ever were to have some notion of global consistency. Then it would be really fragile, so it is worth of improving this, I think. Miroslav