From patchwork Fri Oct 4 16:03:30 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Michael Tokarev X-Patchwork-Id: 832731 Delivered-To: patch@linaro.org Received: by 2002:adf:8b52:0:b0:367:895a:4699 with SMTP id v18csp855389wra; Fri, 4 Oct 2024 09:06:51 -0700 (PDT) X-Forwarded-Encrypted: i=2; AJvYcCW4BaCIl4FIPrZiFUiyE4lWnl4TOKsQANUJRjmB8loNFSppvFoB/YK14n5skWBtSt9S6zGr4Q==@linaro.org X-Google-Smtp-Source: AGHT+IE325H4U1zCqg1APEDZvMU26KJgAzWUO815U9ZLDPKDJfOiKrvXIiUDeuafSo21tsVk0xdu X-Received: by 2002:a05:6102:4413:b0:4a3:d9da:16d6 with SMTP id ada2fe7eead31-4a405745621mr2864529137.3.1728058011319; Fri, 04 Oct 2024 09:06:51 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1728058011; cv=none; d=google.com; s=arc-20240605; b=gfmq2K9dd+QbnRjdB8bWTlj155Vsc2ghWiRJLml/4Ac1PDNEB0a7yrpiTYez3c3z+I sRtI2XsKu+mUMztk+Kwo1RugMxgucwsn0wr1xdSkOJRrexZ7ys79pg6YLwBeysvm2qrB Sgv48/rypgMCdzPtZoXJzKUjuo8ES89QagczfNhhXZ2UntOrYsfQaj53MtTZmgLabbq7 LH/fHFuhPaZ0w38FscllzOmUxWrPugn9jIvEKS0fb+Ji8Y2uT6V/ebLhAspnGZSKFbnJ p3LQQJynyUt+7v9uOSWlhcU9I1PZBuUzWkyWWyBegfBfneZhyZRfPKzWLlpzIJTGAFs3 RSzg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20240605; h=sender:errors-to:list-subscribe:list-help:list-post:list-archive :list-unsubscribe:list-id:precedence:content-transfer-encoding :mime-version:references:in-reply-to:message-id:date:subject:cc:to :from; bh=jT+zooujVsLGzoT20mG6BKHIJ5eh2+ZlFdB/TXo6FsI=; fh=cS2Tln+tR873plP2hbRuf2Uwh4g+jngXB8rVjwPMBIk=; b=G+48sroI5zSJ891dSfeMyzm2bOKg2NMnoLJpXzVxFqGQTBv3nQSYvu3x1GtjMm7wly jH1bYMGgHlQRLHK7GmUfnynNVuWSuA0Dix1d1Nn803DqWOGW6F8xeEcecE+vm03N6gBk C+dYw2Z07y3ChSNOGuu5Ow1zRwTFG3Vqb3PdDZC1wuvRbGh0CBXYVR8kG4LYhjjuul/4 /dOtII4hvS3IzWcCnIU0tdDV7V81tvQrSjKx9rjTNKQkRENGmJLcsK5Md5O3Py81uGDQ fqM2JmO1TGRuo/jJMaOn74Uz8ZCDTiYbjkyV2CkM/4lvShvw5dYaR600Kx5Gmf+AwXqG cLjA==; dara=google.com ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of qemu-devel-bounces+patch=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom="qemu-devel-bounces+patch=linaro.org@nongnu.org" Return-Path: Received: from lists.gnu.org (lists.gnu.org. [209.51.188.17]) by mx.google.com with ESMTPS id ada2fe7eead31-4a412e8f926si13076137.272.2024.10.04.09.06.51 for (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Fri, 04 Oct 2024 09:06:51 -0700 (PDT) Received-SPF: pass (google.com: domain of qemu-devel-bounces+patch=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; Authentication-Results: mx.google.com; spf=pass (google.com: domain of qemu-devel-bounces+patch=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom="qemu-devel-bounces+patch=linaro.org@nongnu.org" Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1swkoM-0005ef-Ln; Fri, 04 Oct 2024 12:05:47 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1swkoJ-0005QP-Eb; Fri, 04 Oct 2024 12:05:43 -0400 Received: from isrv.corpit.ru ([86.62.121.231]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1swkoH-0001xw-IM; Fri, 04 Oct 2024 12:05:43 -0400 Received: from tsrv.corpit.ru (tsrv.tls.msk.ru [192.168.177.2]) by isrv.corpit.ru (Postfix) with ESMTP id F00D59557B; Fri, 4 Oct 2024 19:03:30 +0300 (MSK) Received: from tls.msk.ru (mjt.wg.tls.msk.ru [192.168.177.130]) by tsrv.corpit.ru (Postfix) with SMTP id 3519814D989; Fri, 4 Oct 2024 19:03:33 +0300 (MSK) Received: (nullmailer pid 1282572 invoked by uid 1000); Fri, 04 Oct 2024 16:03:32 -0000 From: Michael Tokarev To: qemu-devel@nongnu.org Cc: Peter Maydell , qemu-trivial@nongnu.org, Michael Tokarev Subject: [PULL 22/23] docs/devel: Mention post_load hook restrictions where we document the hook Date: Fri, 4 Oct 2024 19:03:30 +0300 Message-Id: <20241004160331.1282441-23-mjt@tls.msk.ru> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20241004160331.1282441-1-mjt@tls.msk.ru> References: <20241004160331.1282441-1-mjt@tls.msk.ru> MIME-Version: 1.0 Received-SPF: pass client-ip=86.62.121.231; envelope-from=mjt@tls.msk.ru; helo=isrv.corpit.ru X-Spam_score_int: -68 X-Spam_score: -6.9 X-Spam_bar: ------ X-Spam_report: (-6.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+patch=linaro.org@nongnu.org Sender: qemu-devel-bounces+patch=linaro.org@nongnu.org From: Peter Maydell Accessing another device in a post_load hook is a bad idea, because the order of device save/restore is not fixed, and so this cross-device access makes the save/restore non-deterministic. We previously only flagged up this requirement in the record-and-replay developer docs; repeat it in the main migration documentation, where a developer trying to implement a post_load hook is more likely to see it. Signed-off-by: Peter Maydell Reviewed-by: Philippe Mathieu-Daudé Reviewed-by: Michael Tokarev Signed-off-by: Michael Tokarev --- docs/devel/migration/main.rst | 6 ++++++ docs/devel/replay.rst | 3 +++ 2 files changed, 9 insertions(+) diff --git a/docs/devel/migration/main.rst b/docs/devel/migration/main.rst index 784c899dca..c2857fc244 100644 --- a/docs/devel/migration/main.rst +++ b/docs/devel/migration/main.rst @@ -465,6 +465,12 @@ Examples of such API functions are: - portio_list_set_address() - portio_list_set_enabled() +Since the order of device save/restore is not defined, you must +avoid accessing or changing any other device's state in one of these +callbacks. (For instance, don't do anything that calls ``update_irq()`` +in a ``post_load`` hook.) Otherwise, restore will not be deterministic, +and this will break execution record/replay. + Iterative device migration -------------------------- diff --git a/docs/devel/replay.rst b/docs/devel/replay.rst index effd856f0c..40f58d9d4f 100644 --- a/docs/devel/replay.rst +++ b/docs/devel/replay.rst @@ -202,6 +202,9 @@ into the log. Saving/restoring the VM state ----------------------------- +Record/replay relies on VM state save and restore being complete and +deterministic. + All fields in the device state structure (including virtual timers) should be restored by loadvm to the same values they had before savevm.