From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 406324266B9 for ; Thu, 21 May 2026 20:35:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779395758; cv=none; b=GtjP9Q701xeFmoc9plodL34F9WCmK0RYvmaQc1P7RMqhbcv/2T7CKvzPmpNrfgAcgY0A+ng8Nsc4HYXdy7WF3kHwN1g6pD2FBXc2dcyKjcgMSaTRSn1sPFWWI4t8ABMMIQggLROosoiWHeWEtbUw2SY4kXSU5JVtBnVrO77Sx2I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779395758; c=relaxed/simple; bh=ipWhDnS3c8Of+slJErBTF5Vqt6ODkaCbWe9MFVov0zI=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=gSrtpGxJuqe2X0i2nvsd6yYd/6HbimBVIHtsayjR6mvC7XptqJINnUXLhmhiw0to6p2OLMPwSis7p5pxQa7zTFmcjNXAFw3d/UNE46Rr+rwqtkRFNzx7u6RjGxBUTHxZ4fsuWK3fJY0scfP3jvJ0I3N7xfmZmenSZJP+C+nD0bg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=lkacSS6N; arc=none smtp.client-ip=209.85.214.201 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=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="lkacSS6N" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-2ba838d3fa4so62296195ad.3 for ; Thu, 21 May 2026 13:35:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1779395754; x=1780000554; darn=lists.linux.dev; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=ipWhDnS3c8Of+slJErBTF5Vqt6ODkaCbWe9MFVov0zI=; b=lkacSS6NGUgZGw0MKI4O7j2c5hHkNv9Yhd806a88XULF/5eJJUDVthjR/O/u71b6GK 4Z1XhN/9E5VNHIRt/B0PWaDvW2Ee9UOV6k4QHt99x47UGRCSlBeWhjdUfHzOZRt1zYct FxEDKf970lSr+135Ze3Kzi/Z/OzKhG4nfOGujxsO8lHtNUH03fzm6ecMTOnIEujy5nYT 4W7B6Osl0kJwmzTJEsduJn/PnsRhMqUancVDLW84fjk+ysdnH6p563axTyRtD2uFrhAx NYsMqXG41ofrZlHN30x/AA919Fcf2zRYwjJSwj0j63b1U7xvSDqOnJgKjLIHxk+AWOTu 95Zg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1779395754; x=1780000554; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=ipWhDnS3c8Of+slJErBTF5Vqt6ODkaCbWe9MFVov0zI=; b=l6Uvj+dh7s0Zb+q5gzIAqJDc0RFRk19Pk6GvaM3dZeUhSir4b/YD5mcQ3bGnAaeWGv 1xlwb1da6FplWzmqgrwYynQCCPtHfN4+l5YMtZwsFRJIDPI2RgLGm4QXcOyKljpNqIHw v8lcGyV+evN2Y0EPghu2qX/Ev+nbeo2ZNBP8BcE2U1ZBhPCmDhsWi+ZaoPzgOCqZkbis lN42NuXtw7LexLP2B6AvPUBAZcohw0IKB36QD7AD+tFVteGwBiiAQ7AlvlkyuQQRJiWa YUJ2zRDf10UOxo2IyE2QIXMLCMiMbMCunPkNnnI5TcJc6/Tkr/4y8oEVr/wH26rNMgNV 1t5Q== X-Forwarded-Encrypted: i=1; AFNElJ9AEyrFyr8AvgA5liEqT0A4bUlNZCTdBvTnCbluFyhjyE/apAh1ZQ87RQFkpYGanSu1Z8xU3n6AgeYCLqChOw==@lists.linux.dev X-Gm-Message-State: AOJu0Yy6d09U7EEqV710/zP5Qs7IWCkJgokzYW8tzGQNhLD2NxboZafT EflI6EM0sfPzuuJEvRhNyej+alxpzh2XIsaB62j9FCfFWY5IPGO6hR39w90Nqpz/citTIMwryM6 /ltewiA== X-Received: from pglv7.prod.google.com ([2002:a63:1507:0:b0:c80:192c:51ff]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:d491:b0:3b2:8677:813e with SMTP id adf61e73a8af0-3b328ec5909mr476744637.42.1779395753857; Thu, 21 May 2026 13:35:53 -0700 (PDT) Date: Thu, 21 May 2026 13:35:53 -0700 In-Reply-To: <13d79ba1e0450068c9573ccd8deb3ec007aea8d6.camel@infradead.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260515191942.1892718-1-seanjc@google.com> <20260515191942.1892718-30-seanjc@google.com> <13d79ba1e0450068c9573ccd8deb3ec007aea8d6.camel@infradead.org> Message-ID: Subject: Re: [PATCH v3 29/41] x86/paravirt: Plumb a return code into __paravirt_set_sched_clock() From: Sean Christopherson To: David Woodhouse Cc: 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 , 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 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Thu, May 21, 2026, David Woodhouse wrote: > 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 ca= n > > 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 genera= lly > > 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 >=20 > Oooh... can we use this to reject the kvmclock when we have a stable > and reliable TSC even for non-CoCo guests? Yes, but I would much rather "fix" kvmclock to not even attempt to register= itself as the sched_clock (which this series does).