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 X-Spam-Level: X-Spam-Status: No, score=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C66ADC433DB for ; Thu, 18 Mar 2021 10:19:56 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 29A5364E90 for ; Thu, 18 Mar 2021 10:19:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 29A5364E90 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:60998 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lMpkx-0000W6-5P for qemu-devel@archiver.kernel.org; Thu, 18 Mar 2021 06:19:55 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53366) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lMpk6-0008Be-VF for qemu-devel@nongnu.org; Thu, 18 Mar 2021 06:19:02 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:28074) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lMpk3-0006hX-Jd for qemu-devel@nongnu.org; Thu, 18 Mar 2021 06:19:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1616062737; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Pw9N8S2fyBYvhZbaLRvZkk8jgbOcQTbuuRuN0Jxr0y0=; b=NgtGOrGo+K3n/316sYncF37X8MRv7K0zsrCf0L4wv9wpmmZQumO2+B+mHZymo7sBrppq2S XLBVjmNu/rkTJ/226K+KCb45TfUsuYaH2LyiD113rVp6EMBBIINK6jier/HuzfsGnO7vPQ moIo3Blt28LNlDLKjX6vK9MY/qsD2zU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-331-jpk_k9dSNGKWTBWuYqrpIA-1; Thu, 18 Mar 2021 06:18:53 -0400 X-MC-Unique: jpk_k9dSNGKWTBWuYqrpIA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 33FD481431C; Thu, 18 Mar 2021 10:18:52 +0000 (UTC) Received: from work-vm (ovpn-115-13.ams2.redhat.com [10.36.115.13]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0549C6F96F; Thu, 18 Mar 2021 10:18:50 +0000 (UTC) Date: Thu, 18 Mar 2021 10:18:48 +0000 From: "Dr. David Alan Gilbert" To: Peter Maydell Subject: Re: of AVR target page size Message-ID: References: MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=216.205.24.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.251, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Richard Henderson , Michael Rolnik , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Peter Maydell (peter.maydell@linaro.org) wrote: > On Wed, 17 Mar 2021 at 20:17, Dr. David Alan Gilbert > wrote: > > > > Hi Michael, > > I noticed your AVR code defines: > > > > #define TARGET_PAGE_BITS 8 > > > > and has an explanation of why. > > > > Note however that's not going to work with the current live > > migration/snapshotting code, since you're a couple of bits smaller > > than the smallest page size we had so far, and for many years > > the RAM migration code has stolen the bottom few bits of the address > > as a flag field, and has already used 0x100 up; see migration/ram.c > > RAM_SAVE_FLAG_* - and it's actually tricky to change it, because if > > you change it then it'll break migration compatibility with existing > > qemu's. >=20 > If you want to use low bits as flags for other stuff, you > should have a compile time assert that you have the number > of bits you expect, or otherwise force a compile error. > Otherwise you'll end up with unpleasant surprises like this one... Yes, I think that's been around for a long time. > I think that for the cpu-all.h uses of low bits we would > end up with a compile error for excessively small TARGET_PAGE_BITS > because we define the bits like this: > #define TLB_DISCARD_WRITE (1 << (TARGET_PAGE_BITS_MIN - 6)) > and I expect the compiler will complain if the RHS of the '<<' > is a negative constant. But I don't know if that's deliberate > or a happy accident :-) Something like this, does fail for AVR: >From 8a617836955ebba1a4932d238fce600be51b9182 Mon Sep 17 00:00:00 2001 From: "Dr. David Alan Gilbert" Date: Thu, 18 Mar 2021 10:17:27 +0000 Subject: [PATCH] migration: Check TARGET_PAGE_SIZE vs RAM flags migration/ram.c steals the bottom few bits of address for flags; check that we don't run into TARGET_PAGE_SIZE Signed-off-by: Dr. David Alan Gilbert --- migration/ram.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/migration/ram.c b/migration/ram.c index 1ee7ff9c6d..f053d45f3c 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -81,6 +81,8 @@ /* 0x80 is reserved in migration.h start with 0x100 next */ #define RAM_SAVE_FLAG_COMPRESS_PAGE 0x100 =20 +#define RAM_SAVE_FLAG__MAX RAM_SAVE_FLAG_COMPRESS_PAGE + static inline bool is_zero_range(uint8_t *p, uint64_t size) { return buffer_is_zero(p, size); @@ -4101,5 +4103,10 @@ static SaveVMHandlers savevm_ram_handlers =3D { void ram_mig_init(void) { qemu_mutex_init(&XBZRLE.lock); +#ifndef TARGET_PAGE_BITS_VARY + QEMU_BUILD_BUG_ON(RAM_SAVE_FLAG__MAX >=3D TARGET_PAGE_SIZE); +#else + QEMU_BUILD_BUG_ON(RAM_SAVE_FLAG__MAX >=3D (1 << TARGET_PAGE_BITS_MIN))= ; +#endif register_savevm_live("ram", 0, 4, &savevm_ram_handlers, &ram_state); } --=20 2.30.2 > thanks > -- PMM >=20 --=20 Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK