From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F34BC3A1CF4; Wed, 3 Dec 2025 16:52:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764780730; cv=none; b=f7hdYpxS0TZlRyJ6Y3mN5WSN1+MgV9OsHdG6qRKI31wArpUWLaENjk+Le4yx0yNISpkbnz/76FFUESy/FVOAMSomYNB6hW3hriak8NOzEWqoHc66cOttBQhBC4t3ahgYNkJC1OZLd58gRo+NnZcHmLG3qS27jsKsQumrwP2NFWI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764780730; c=relaxed/simple; bh=ff1r0JEDWO5jjpC/c+fKlQRpnYmkS32GNPsAKhRV5+I=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=EgUKj6ENb/92crAaHvQ3Oudk0vBoJBvRCxvChTfH7ChFES/LcAEk4tLpjOnHF1hy+2fX7RjlieChJQRDC9GXEnJdsh1hxGPNB0Ampi/qlacYtYKIKYpLWO/V5yCfQsDZJ5tuu8vJqlewrag57P3iAWjyH/72CPZHHUPaCZklnB8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=desiato.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=lf8cmMZ6; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=desiato.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="lf8cmMZ6" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=N+716RPxYHPXubi1V1mW79jwZ+pLhTxJhm/MCCVNO+g=; b=lf8cmMZ6desTb8fFA5NDu9QpcU 3UmLE9XGSZw7HofiRmkj5oPDHLhY6Gvh6IQihDYGJPSe81AbCozJieBCXPek9FJAoCQn0f5cAMtjz JXE7HYWw3O6pzCd6a4GXvd81sNPcAZcBiPYCco93khu0AI5TaFcKwZ+E/9d2hXoW88ID8slplQCxa oTSAdYn9LLHBPt2orLhdvZdGMcEQDxTYRhi7HFU7VtMylbE5tPRPRUYupyxJ/PK7CZdLk2Cq48xQq KZHbNLl6QZN3+PbMIUp7YOd8E/wArs03ia2nF+c639lQnP4J5I9CZT7nPbZfcB7KPdLCMoqF46KjZ stVMs6uA==; Received: from [172.31.31.148] (helo=u09cd745991455d.lumleys.internal) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vQpDf-00000002Xsn-0QUF; Wed, 03 Dec 2025 15:56:43 +0000 Message-ID: Subject: Re: [PATCH v3 2/4] ptp: vmclock: support device notifications From: David Woodhouse To: "Chalios, Babis" , "robh@kernel.org" , "krzk+dt@kernel.org" , "conor+dt@kernel.org" , "richardcochran@gmail.com" , "andrew+netdev@lunn.ch" , "davem@davemloft.net" , "edumazet@google.com" , "kuba@kernel.org" , "pabeni@redhat.com" Cc: "devicetree@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Graf (AWS), Alexander" , "mzxreary@0pointer.de" , "Cali, Marco" Date: Wed, 03 Dec 2025 16:52:02 +0000 In-Reply-To: <20251203123539.7292-3-bchalios@amazon.es> References: <20251203123539.7292-1-bchalios@amazon.es> <20251203123539.7292-3-bchalios@amazon.es> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-bX2ckaGjDK0VfcyzH9jR" User-Agent: Evolution 3.52.3-0ubuntu1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html --=-bX2ckaGjDK0VfcyzH9jR Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2025-12-03 at 12:36 +0000, Chalios, Babis wrote: > From: "Chalios, Babis" >=20 > Add optional support for device notifications in VMClock. When > supported, the hypervisor will send a device notification every time it > updates the seq_count to a new even value. >=20 > Moreover, add support for poll() in VMClock as a means to propagate this > notification to user space. poll() will return a POLLIN event to > listeners every time seq_count changes to a value different than the one > last seen (since open() or last read()/pread()). This means that when > poll() returns a POLLIN event, listeners need to use read() to observe > what has changed and update the reader's view of seq_count. In other > words, after a poll() returned, all subsequent calls to poll() will > immediately return with a POLLIN event until the listener calls read(). >=20 > The device advertises support for the notification mechanism by setting > flag VMCLOCK_FLAG_NOTIFICATION_PRESENT in vmclock_abi flags field. If > the flag is not present the driver won't setup the ACPI notification > handler and poll() will always immediately return POLLHUP. >=20 > Signed-off-by: Babis Chalios Mostly looks good to me; thanks. However...=20 > +static __poll_t vmclock_miscdev_poll(struct file *fp, poll_table *wait) > +{ > + struct vmclock_file_state *fst =3D fp->private_data; > + struct vmclock_state *st =3D fst->st; > + uint32_t seq; > + > + /* > + * Hypervisor will not send us any notifications, so fail immediately > + * to avoid having caller sleeping for ever. > + */ > + if (!(st->clk->flags & VMCLOCK_FLAG_NOTIFICATION_PRESENT)) > + return POLLHUP; Missing le64_to_cpu() there. And I guess *strictly* speaking we should do the seq_lock dance=C2=A0whenever we read the dynamic fields, although that only ever matters if a hypervisor were to bump seq_count to an odd value, *then* set the VMCLOCK_FLAG_NOTIFICATION_PRESENT flag, then clear the flag again before bumping seq_count to even, and blame the *guest* for looking at the wrong time. Which is frankly insane, and I don't think I care. So with the le64_to_cpu() added,=20 Reviewed-by: David Woodhouse Don't post again for a few days though; three versions in 48 hours is enough :) > +static int vmclock_miscdev_release(struct inode *inode, struct file *fp) > +{ > + kfree(fp->private_data); > + return 0; > +} Still bugs me a little. I note simple_attr_release() is exported and does the same, but I guess we'd want to move and rename that before we try to use it from places like this. --=-bX2ckaGjDK0VfcyzH9jR Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj jfhCFqxYyRiW8g3cNFAvltDbK5AzcOaR7yVzVGadr4YcCVxjKrEJOgi7WEOH8rUgCNB5cTD8N/Et GfZI+LGqSv0YtNa54T9D1AWJy08ZKkWvfGGIXN9UFAPMJ6OLLH/UUEgFa+7KlrEvMUupDFGnnR06 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