From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=209.85.214.180 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794327836; b=PPawI47qPboKwHWfQJKQI+63mK5UmHnbqVUhNW1LB7P6B2x2SMJP3o5YuMjceQWyGBiO a5+Wl7VyVP9FebTWkxQs4qDNoimfmZLLQ3YrMbJr09cjjJrpkj2hgMBYQ+ljbZaFsn5hW sWLGhCNJVkZhUpil6PUJIgkBGHJQAsEEInxD6r1wfCyH9fbn4HXggv8O1CHlpnD8mWIjn ouKAJloMudwOprmV4UjZszeOrLINTmHPR0AqLJTWT03eoR2MwcrHKaJZrkkGRNhwCIK9j 3o1jqpMvueCAYzdqFh+Yx3EwpLa21krC+0Fx44zk/TJLZulOokkj63lEIxdlZwUsyAw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794327836; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received:Received: Mime-Version:Content-Transfer-Encoding:Content-Type:Date:Message-Id: Cc:Subject:From:To:X-Mailer:References:In-Reply-To; bh=Mw9iOCkEBWkvxdLSgoJVCB6jT3T4ThA8jIPRTFH0lnY=; b=zN0cwEeC1dfVm+2rYmqQpUutvoRPPluvXYXPEBICzaeDU3i5n8HAzuBztBu4/x3xn1zT l3UdMf4P7blH5Vc2Ut+qTmYvCcDFjihN4Q0wlS68Lmu7+Q6G5DnG56pwJPGTOliUMPXxx 8MHKq67Rptesapf3Db9RvlCHjGO4fm+znCpm87BdJOqaVzEJ5KHJ57rziAJPo9UOqpNQL eT/sjhLmMqZIoMcjkf4sIHbebpKwdMTd2KXmy4y6CjyzfiXwsPei+dzsNp2bbMzwZmRgo MJdReODb7ykzAqXF6I400iB1i63B/i2DfpTDfupvAsJ8gs94ywQxJJ774pW3d8dT6bw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=google.com; spf=pass smtp.mailfrom=google.com; dkim=pass header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20260707 header.b=VSPzJL76; arc=none smtp.remote-ip=209.85.214.180 Received: from mail-pl1-f180.google.com (mail-pl1-f180.google.com [209.85.214.180]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 383F4606A326 for ; Tue, 10 Nov 2026 16:23:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 383F4606A326 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20260707 header.b=VSPzJL76 Received: by mail-pl1-f180.google.com with SMTP id d9443c01a7336-2e987a2ba0cso13295045ad.3 for ; Tue, 10 Nov 2026 08:23:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20260707; t=1794327836; x=1794932636; darn=vger.kernel.org; h=in-reply-to:references:to:from:subject:cc:message-id:date :content-type:content-transfer-encoding:mime-version:from:to:cc :subject:date:message-id:reply-to:content-type; bh=Mw9iOCkEBWkvxdLSgoJVCB6jT3T4ThA8jIPRTFH0lnY=; b=VSPzJL76+wTF7+tRHaTvgknu/rdXasZus90UA5dew9kegykwMMzKH/F1V6GxO7RQBH 4/OoTFVOHyB4E03Dq2sjac2puiHJm+c4fvoFKJLJ6EEpCLTW90+KxQKP8Xk4x1JCosEq Qn1NC6kr4qdwt4JzE8ObsRxCsUeZmKjtT2SBeeizeKBMIl7bOARS8kw8yLezlhGZJVv0 o52jzOWxsMkIIBT3ThUaLCPi/QAmSZxKSqqb6hMrak99PMeAxD3u0dk/TP7xs21D2Iw/ Ez/eieBRGPY5ouf/XdRZ3e00nlnuno9Ot9UU0ZRzVZtwWy7hL9Ca1MHSbWRqNGS8EsIb 6SQA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1794327836; x=1794932636; h=in-reply-to:references:to:from:subject:cc:message-id:date :content-type:content-transfer-encoding:mime-version:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=Mw9iOCkEBWkvxdLSgoJVCB6jT3T4ThA8jIPRTFH0lnY=; b=u5ntUKsYMTkzTUx+gnUK6dXjZNDp5dpmFxEYFntW9qSBDjw9gv5S7lbNmdbp4hZsok 2J5/1AoRdIl4CspLXlHIH2TFnUs8DRObAhMPeHG05fxEZlaqUrsvmjqTtLmLw/+0danM QecFm/bUFjZCim7r7adhVEOOS6gVLJIbK61n0Seu9hn+I7r7X8YhaHCaeOx/POctx+k+ PHo1NSOI9kq8ZSJ2rMlUF6Ae36+yx7sshu9O4g2iB0e7LRNSHVtoa4fO2sa5maFNENEA ZGmWs2CMp+euTBSGOUi2NfRda7JaQiXAkHiLIBf4dW7Nygx8O0JZ2skJQP+o8FsWbpZT rpdA== X-Forwarded-Encrypted: i=1; AL+hErGVLy/tK2P61NRoPQ2mTtguT3Kju0EyYqynroWSI56Y6KtZzV8zSdfy/uTTXRdwtWQ1isM=@vger.kernel.org X-Gm-Message-State: APuU4Z/gfWvy0d02cWvxEcuRcIC9h+fTfIxlxjIqknbyyMx4Jgff0BcQ XF1Ch39ovD14F4lWF2vdJJ8RPVMYUduFNan90cxohRHU3/+unBgiTEg0o9uombW4+Q== X-Gm-Gg: AYBFou01+WZUhHXAgX++P82603jr01BbKtbRBiRyMs+x+9lueNHEm9NrkQEkt00b7gJ Jh3U699qAeyjOFiFZgtl+D1cKNvidIPByyuhJLI/2vhsEjG7GP4sRMtE/ra84eiN5nH5GUaD1Ev AEdeqpaYsJmpwxhe5v4ZsUVvvPDorBb96FoZzxn0epNKW8IbsOQVxF1Yg4odmvs5zdHlE/jUaLV 0YIMNq5ZZexXPW1QZvOCrSUvPfjj002HmWYthg/3gyPivO2tIlryLCqTb4VBW/XDDpDD608G0Mb p8+H+PaNmMOK209FhOrrVx4fpJVXHq9RTKWuZtdSssxr4/wydLJMheC9kOo1MqzrFo4FIHWtKw3 1Fwtvekj19WnfeQArn6hPnZsBcS0mHrcpaUm6Rx6gqQfxQoM4s4/uYee+YK1TX1ZZq9YNe9D1w8 tQXGXuGwidPxaBmZvJ7rv+rNg9fibERNoC9MGfCyrKtJ4nippReR+GvnmCzBPoyZfJaFYWkJWHU Oeg/8V42o0vJDb5wsLqWD+8Vet5mo7T/9VYQ6dt/6jMe0TxFnkfmb0FvPokh26etO86FeCmyAc2 Wx0JvzTLEMxJwHTB2l5pOoY3vfl4yj8V78bmNs6yI1uXnvWZvV7H9ArAPahNhggc X-Received: by 2002:a17:902:d4cc:b0:2e8:18ca:5f46 with SMTP id d9443c01a7336-2edb9146ba8mr28990585ad.14.1794327834955; Tue, 10 Nov 2026 08:23:54 -0800 (PST) Received: from localhost (33.79.127.34.bc.googleusercontent.com. [34.127.79.33]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2edb6d7d964sm11306915ad.32.2026.11.10.08.23.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Nov 2026 08:23:54 -0800 (PST) X-Mailing-List: kvm@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Tue, 10 Nov 2026 16:23:53 +0000 Message-Id: Cc: , , "Pratyush Yadav" , , , , , , , , , Subject: Re: [PATCH v4 16/19] PCI: liveupdate: Add feature header to struct pci_dev_ser From: "David Matlack" To: "Tarun Sahu" , "Pasha Tatashin" , "Mike Rapoport" , , , , "David Matlack" , "Alexander Graf" , , , , , , , "Bjorn Helgaas" , , , , , "Andrew Morton" , , X-Mailer: aerc 0.21.0 References: <20261110050202.529473-1-tarunsahu@google.com> <20261110050202.529473-17-tarunsahu@google.com> In-Reply-To: <20261110050202.529473-17-tarunsahu@google.com> On Tue Nov 10, 2026 at 5:01 AM UTC, Tarun Sahu wrote: > Precede each serialized PCI device entry in the PCI Live Update KHO block > set with struct kho_ser_hdr via DECLARE_KHO_SER so future per-device PCI > Live Update features can append fields to struct pci_dev_ser without > breaking compatibility between adjacent kernels. Elements of a collection should not have their own feature headers. This applies to patches 10, 12, 14, 16 and 18. I raised this during the v2 discussion [1][2], but I don't think it was addressed. All entries in a KHO block set are written by the same kernel using the same struct, and the block set has a single entry_size, so every entry header is necessarily identical. They don't convey anything that the header of the struct that owns the collection can't. In this case, struct pci_ser's header can define features that describe fields in struct pci_dev_ser, and the PCI core checks them once before iterating. If a feature only applies to some devices, the field's value in each entry says whether that device uses it. Per-entry headers also cost a lot for small entries. struct pci_dev_ser goes from 8 to 16 bytes, and to 24 bytes once the first feature is added. Patch 18 does the same for every preserved memfd folio, which for a large guest backed by 4K pages adds gigabytes of preserved metadata. They also add new ways to read out of bounds. kho_ser_payload() trusts nr_required/nr_optional in each entry, and nothing checks that the entry header plus payload fit within entry_size. In patches 14 and 18 the walk uses each entry's fhdr->size to find the next entry, so one bad header throws off every entry after it. Instead I would keep struct pci_dev_ser as a plain struct, take the entry size from the KHO block header (patch 2), and in pci_flb_retrieve() check once that the entry size covers the base fields, plus the fields of any features set in struct pci_ser's header, e.g.: entry_size =3D kho_block_set_entry_size(&incoming->block_set); if (entry_size < offsetofend(struct pci_dev_ser, refcount)) panic(...); That also restores the minimum entry size check that the v10 PCI series had with PCI_DEV_SER_MIN_SIZE, which this version drops. [...] > - kho_block_set_init(&incoming->block_set, sizeof(struct pci_dev_ser)); > + kho_block_set_init(&incoming->block_set, kho_ser_size(pci_dev_ser)); This size is never used. kho_block_set_restore() overwrites it with the entry size recorded by the previous kernel. Passing this kernel's size here is misleading: pci_flb_retrieve() (and the LUO session/file restore paths) read as if they iterate incoming entries with the outgoing entry size, which would be a bug. Incoming block sets should not take an entry size at all. kho_block_set_restore() should initialize the block set itself from the incoming block headers, and the incoming paths should drop the kho_block_set_init() call. [1] https://lore.kernel.org/kexec/atl6K2Juy6Bh29lh@google.com/ [2] https://lore.kernel.org/kexec/at-8vkVpN2SF3XgB@google.com/