From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 01D4C226549; Thu, 6 Feb 2025 09:32:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738834373; cv=none; b=QlpRf4Q/dpv8C4fE//1TBJViCvIW/a7XWemcCcfFMC2lWrEQ3hYxjoxB+c5CLDsks8XbUAmQLH8PWC61hS+PvMO4X3fy3j4LGe2Y3FGgWnu/MWe5HNHiermrte+S6E9zaIa93DpZexDrN7fHI1d6dUeWFF9/WZbhRKFXqgEYMPE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738834373; c=relaxed/simple; bh=o+Z0681jYsiHqmh3U0IYwEJZRDAlvJSN/vbRjprW+rk=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=WOQtt2RvYoSx5xf60QUgB5TETC7dHmzu55kmJsbaiQwDpeIA33JHiKmqpP035K0ZlvPSOvxSRMcG6qi311w3CL0H7oT46Q5cTF1QsTMWZuDC0sahafz99UhjEUUVbnR9TBMdpACZz1yPzI5n+2DQLAjlOr9dkVzZZ/LdW2Rj+dQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=casper.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Ub5LxYYO; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=casper.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Ub5LxYYO" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; 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=ygCyX4kIzHTkCMIYfhFggV+w58QHYc5sCxu+XxJ0VuY=; b=Ub5LxYYOtNPsBxcWCz/qYQ+WX4 912GkRIsrEX9TSN/bszxcLHH+DpQQY46NZqIZdqBSvshZenQO1rM7ipB/pWGF5WK67YhzgldvIjOS 7eebgxztX8C450yP9UK7d8huLYU+VU4SGE9ZwPvNvSJSAJEsRlvhv33RN/UuP93usPGDRk7byAFEY +iM/qVTX3BwYOld1a5a5yz9TwJ7uK61w3cZcjmN9OCacvjJMvPym99zqddq2ryvHsaimV6QMYONQ3 Zac1W3JvkwqaP5CP5fHHpHQUCYBAnmfgJNS6m2IgeLj4+GTxjffClRIxzP6B7tthDHyW5qqI8wvpn N6v8/LFA==; Received: from [54.239.6.187] (helo=freeip.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tfyEc-00000005lug-1GF0; Thu, 06 Feb 2025 09:31:46 +0000 Message-ID: Subject: Re: [PATCH v3 00/18] vDSO: Introduce generic data storage From: David Woodhouse To: Thomas =?ISO-8859-1?Q?Wei=DFschuh?= , "James E.J. Bottomley" , Helge Deller , Andy Lutomirski , Thomas Gleixner , Vincenzo Frascino , Anna-Maria Behnsen , Frederic Weisbecker , Andrew Morton , Catalin Marinas , Will Deacon , Theodore Ts'o , "Jason A. Donenfeld" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Huacai Chen , WANG Xuerui , Russell King , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Thomas Bogendoerfer , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Naveen N Rao , Madhavan Srinivasan , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Arnd Bergmann , Guo Ren Cc: linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-riscv@lists.infradead.org, loongarch@lists.linux.dev, linux-s390@vger.kernel.org, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-arch@vger.kernel.org, Nam Cao , linux-csky@vger.kernel.org, "Ridoux, Julien" , "Luu, Ryan" , kvm Date: Thu, 06 Feb 2025 09:31:42 +0000 In-Reply-To: <20250204-vdso-store-rng-v3-0-13a4669dfc8c@linutronix.de> References: <20250204-vdso-store-rng-v3-0-13a4669dfc8c@linutronix.de> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-TLRPvEdtMvxq/eM5U95X" User-Agent: Evolution 3.52.3-0ubuntu1 Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html --=-TLRPvEdtMvxq/eM5U95X Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2025-02-04 at 13:05 +0100, Thomas Wei=C3=9Fschuh wrote: > Currently each architecture defines the setup of the vDSO data page on > its own, mostly through copy-and-paste from some other architecture. > Extend the existing generic vDSO implementation to also provide generic > data storage. > This removes duplicated code and paves the way for further changes to > the generic vDSO implementation without having to go through a lot of > per-architecture changes. >=20 > Based on v6.14-rc1 and intended to be merged through the tip tree. Thanks for working on this. Is there a plan to expose the time data directly to userspace in a form which is usable *other* than by function calls which get the value of the clock at a given moment? For populating the vmclock device=C2=B9 we need to know the actual relationship between the hardware counter (TSC, arch timer, etc.) and real time in order to propagate that to the guest. I see two options for doing this: 1. Via userspace, exposing the vdso time data (and a notification when it changes?) and letting the userspace VMM populate the vmclock. This is complex for x86 because of TSC scaling; in fact userspace doesn't currently know the precise scaling from host to guest TSC so we'd have to be able to extract that from KVM. 2. In kernel, asking KVM to populate the vmclock structure much like it does other pvclocks shared with the guest. KVM/x86 already uses pvclock_gtod_register_notifier() to hook changes; should we expand on that? The problem with that notifier is that it seems to be called far more frequently than I'd expect. =C2=B9 https://gitlab.com/qemu-project/qemu/-/commit/3634039b93cc5 --=-TLRPvEdtMvxq/eM5U95X 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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