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 5C01A3CD8A7; Wed, 20 May 2026 23:44:27 +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=1779320670; cv=none; b=Wfe397w0t83QTPo6syFr3C3ru2MJfotwVQpn+1BPIzStlVFR29a03CLKpP8kj2YqCM8AfZydO2hh7Qe9xEJxLoKFEXhI9HETKK94TSOslNguew9ra9HGNmrNuiB89TjZYrizoQT06zagSgTbjmXNEIBb61RkjcoP/Duah7juXNU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779320670; c=relaxed/simple; bh=X0zCw9VggqDwYjpyrxBUVYwfytHsLKivEOlU4sByJ9Y=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=V2BafkFZkD2/nP/vV7vUlfztLXmki7iuv8ykj+a/dN6+wZF0aDX4Spi9yxAiRgAN8kFM73MxEfxZsB3y7jyFVRyPeIKHoaxzJZkrSNXAgo9p66XL6agA5cvgiGtKhawF0fOKS3yKNnpX0TNpL2p1y+qJQEGx28UqDWCOEuz2Feo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (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=h+XaFM8L; arc=none smtp.client-ip=90.155.50.34 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=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="h+XaFM8L" 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=X0zCw9VggqDwYjpyrxBUVYwfytHsLKivEOlU4sByJ9Y=; b=h+XaFM8LtWyTBwkkm146kzpDiU 1WqJWfaHfkn9U0mCSnCi2lUtr2wv3X+MNS5sFKYGHvH3nVkPO9OJJESVl+aTCFDebY6bnnJ8mEzq8 MvfRx9Qa2QDidPBjSWpqG8QUNwFF3Zh8W5xVTIdqpDivSWZk/PaPjCLf4kC+EK1D8qSGwfETNF++E VkPsHBFXoaD0uraLCxA/UKvVxnAt74nYLgcR25Q1IM3i6hE4rihu3olRuEniFiM92XFFGFp7PQ4UY 5/YaP8JuMk3fZDfHZcAdAtZcIyEOLb1PGv3JV9f8k4JC7fW97sAiiTzjl+aCFdFNbdgQfkzNRwbPb YmWXFTlw==; Received: from 54-240-197-235.amazon.com ([54.240.197.235] helo=freeip.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wPqaK-00000007l48-0Tuf; Wed, 20 May 2026 23:44:20 +0000 Message-ID: <13d79ba1e0450068c9573ccd8deb3ec007aea8d6.camel@infradead.org> Subject: Re: [PATCH v3 29/41] x86/paravirt: Plumb a return code into __paravirt_set_sched_clock() From: David Woodhouse To: Sean Christopherson , Kiryl Shutsemau , Paolo Bonzini , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Ajay Kaher , Alexey Makhalov , Jan Kiszka , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Juergen Gross , Daniel Lezcano , Thomas Gleixner , John Stultz Cc: Rick Edgecombe , Vitaly Kuznetsov , Broadcom internal kernel review list , Boris Ostrovsky , Stephen Boyd , x86@kernel.org, linux-coco@lists.linux.dev, kvm@vger.kernel.org, linux-hyperv@vger.kernel.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, Michael Kelley , Tom Lendacky , Nikunj A Dadhania , Thomas Gleixner Date: Thu, 21 May 2026 00:44:18 +0100 In-Reply-To: <20260515191942.1892718-30-seanjc@google.com> References: <20260515191942.1892718-1-seanjc@google.com> <20260515191942.1892718-30-seanjc@google.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-tHXnnzm+pwpZbACXpNw8" User-Agent: Evolution 3.52.3-0ubuntu1.1 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev 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 --=-tHXnnzm+pwpZbACXpNw8 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2026-05-15 at 12:19 -0700, Sean Christopherson wrote: > Add a return code to __paravirt_set_sched_clock() so that the kernel can > reject attempts to use a PV sched_clock without breaking the caller.=C2= =A0 E.g. > when running as a CoCo VM with a secure TSC, using a PV clock is generall= y > undesirable. >=20 > Note, kvmclock is the only PV clock that does anything "extra" beyond > simply registering itself as sched_clock, i.e. is the only caller that > needs to check the new return value. >=20 > Signed-off-by: Sean Christopherson Oooh... can we use this to reject the kvmclock when we have a stable and reliable TSC even for non-CoCo guests? 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