From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CF9CEC7EE30 for ; Thu, 2 Mar 2023 10:50:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230060AbjCBKuo (ORCPT ); Thu, 2 Mar 2023 05:50:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36810 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229592AbjCBKul (ORCPT ); Thu, 2 Mar 2023 05:50:41 -0500 Received: from mail.skyhub.de (mail.skyhub.de [5.9.137.197]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 67347231DE for ; Thu, 2 Mar 2023 02:50:39 -0800 (PST) Received: from zn.tnic (p5de8e9fe.dip0.t-ipconnect.de [93.232.233.254]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id E62641EC06F4; Thu, 2 Mar 2023 11:50:37 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1677754238; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=tWz6s9l2WCuAQ512Au4zmKPORo5v7ghhLXhY91mwp3E=; b=pOHIyZx/ODKTp9XHBtVIavPfqNRRgOZCuwYhA7EBjsj9zhO1vyc9Z2XO246n0OWQq7Z9za lQvT7dYs8brvofPKG9cGQPbM6NsiJpmqsi6IDgEaVL8cEiOJhEXDSEOGqI5jm6WyMsYNmV bUHQNu206l7qCzrLiZ8LRj3qHePwpfw= Date: Thu, 2 Mar 2023 11:50:33 +0100 From: Borislav Petkov To: Andy Lutomirski Cc: Linux Kernel Mailing List , Mike Rapoport , Hugh Dickins , the arch/x86 maintainers Subject: Re: [tip: x86/urgent] x86/setup: Always reserve the first 1M of RAM Message-ID: References: <20210601075354.5149-2-rppt@kernel.org> <162274330352.29796.17521974349959809425.tip-bot2@tip-bot2> <7d344756-aec4-4df2-9427-da742ef9ce6b@app.fastmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <7d344756-aec4-4df2-9427-da742ef9ce6b@app.fastmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 01, 2023 at 07:51:43PM -0800, Andy Lutomirski wrote: > This is quite broken. The comments in the patch seem to understand > that Linux tries twice to allocate the real mode trampoline, but the > code has some issues. > > First, it actively breaks the logic here: > > + /* > + * Don't free memory under 1M for two reasons: > + * - BIOS might clobber it > + * - Crash kernel needs it to be reserved > + */ > + if (start + size < SZ_1M) > + continue; > + if (start < SZ_1M) { > + size -= (SZ_1M - start); > + start = SZ_1M; > + } > + Are you refering, per-chance, here to your comment in that same function a bit higher? Introduced by this thing here: 5bc653b73182 ("x86/efi: Allocate a trampoline if needed in efi_free_boot_services()") ? Also, it looks like Mike did pay attention to your commit: https://lore.kernel.org/all/YLZsEaimyAe0x6b3@kernel.org/ And then there's the whole deal with kdump kernel needing lowmem. The function which became obsolete and got removed by: 23721c8e92f7 ("x86/crash: Remove crash_reserve_low_1M()") So, considering how yours is the only report that breaks booting and this reservation of <=1M has been out there for ~2 years without any complaints, I'm thinking what we should do now is fix that logic. Btw, this whole effort started with a799c2bd29d1 ("x86/setup: Consolidate early memory reservations") Also see this: ec35d1d93bf8 ("x86/setup: Document that Windows reserves the first MiB") and with shit like that, we're "piggybacking" on Windoze since there certification happens at least. Which begs the question: how does your laptop even boot on windoze if windoze reserves that 1M too?! > I real the commit message and the linked bug, and I'm having trouble > finding evidence of anything actually fixed by this patch. Can we > just revert it? If not, it would be nice to get a fixup patch that > genuinely cleans this up -- the whole structure of the code (first, > try to allocate trampoline, then free boot services, then try again) > isn't really conducive to a model where we *don't* free boot services > < 1M. Yes, I think this makes most sense. And that whole area is a minefield so the less we upset the current universe, the better. > Discovered by my delightful laptop, which does not boot with this patch applied. How come your laptop hasn't booted new Linux since then?!? Tztztztz Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette