From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f73.google.com (mail-pj1-f73.google.com [209.85.216.73]) (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 E60D33FE675 for ; Fri, 29 May 2026 15:08:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.73 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780067300; cv=none; b=feptRIw+lS4OZNaNrAW0zQ+pFq8slUUS5PYD/Zf5Hzp+WedmvE295b11UzmeQmUbY1+p72jrSeRfZdZO/2l48O9g21UlOQjZ8MRV2tFhhmHwJm/+31c8cxtuCd9Fww9AAToJ2Er/9NVmplVr+W9MCokdb3hmIZCOaZWaEawA+kA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780067300; c=relaxed/simple; bh=cK9bQGlpdv9LZcFmZsWC/IHJdDiSPttcr7RlDSILQVM=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=ZtAzjwbHrmpW9v6WlM9GCdarnTnU/HenUqTXRBB1SgxMPYGiUsNPc+yGUa7VsbFrYStRfU3eAokLujVoA9vpsCPsmWzMqAWM0858abAQrQYsNT7GSDeh3vWqX6c/IRXadlCwqa9OrCoIE24K9oEQbcDOwGN6JCmTCDLE4Ub8aRU= 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=weDHBzgx; arc=none smtp.client-ip=209.85.216.73 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="weDHBzgx" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-36bc5e97950so885477a91.1 for ; Fri, 29 May 2026 08:08:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1780067298; x=1780672098; darn=lists.linux.dev; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=tzOZYRAyrYNaAuUvG5/Y5SZS8EF8Fxjy2/uxgYTIQuI=; b=weDHBzgxIiPxSVdaTyFPixq4Zjea3RPaVEFcJcB+UewSYMr3nc/ljpJvIAdVGxim9Y nH9dO5XltpUZgyvvqby60DVJenbN5hoBFtc4GBeVCU9OPmATq0xRcOOT3hNUGDg74eQ+ TuQSK2Flag6E34/sUvFUyKJjq2Wqx2emY7hWGOWLCVb4Bh2X6ugfWla2tx90i6LqRNzC ygS+p64tI02w6QJdzyAAu3etNLXv5qlypXqTo3Bfi+aVgbUgJHLoJzARorK3lWoo5RRl wFuyCc3Ny4LSCqm4hCjmFOpWwxqoi2Avgjtk0/UXTc1XZ4CzWDna1c+OGEoZoSUcch6j UmUw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1780067298; x=1780672098; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=tzOZYRAyrYNaAuUvG5/Y5SZS8EF8Fxjy2/uxgYTIQuI=; b=cq9W9tdYG+A3jS6zXCOEQYBrBIMYYvprIlwEdANIXRXlHtT1x/A0B5tNz4i1DOXK3J MLiMjWCDLnT0eixiqVDTxC9h3hcq8GSeUTRlpsWQcICQPPtc6UJDs/bSjkbDZrHGUiKX tZF9W1Ux3k7AiRxdQANEe+GxziqOz4bWY9eGTIngVPRW1jTXo6a3BCW4HaavMKe1xlKy 68GJ56WOzL88lWAC0DaPPCpB9JlRUNsA9kMwm0983zGDUYcqHaECyWlBqR4O+CiF1/wE Xrtu3jPb6V548v7Xmh5LKwdydVYuO9nSv364n9OTjfVIiYT35MgAMa7Xyb75LUC4Tg25 W4+w== X-Forwarded-Encrypted: i=1; AFNElJ+vRLyfb51Dl2DoJe5014P952yLVU3BfxtkC2BISoiFr5c/qE9DOdsm4QbticfGOaJqWXGi5Efs3wmg@lists.linux.dev X-Gm-Message-State: AOJu0Ywmzk1AYYQ2eKb1H96z7yis3kwUg0PNF9xPmY8mx620QqlqMDRI ClMjF80ENvy+yljpktx/6qPdtdDUu2QfCPMDfc3yo6QKiOInyFWW5B6rEovJOzbKLyl4qoQF+YJ Rh+CqDQ== X-Received: from pgbbz16.prod.google.com ([2002:a05:6a02:610:b0:c82:253f:d5e6]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:5281:b0:36b:293:68d1 with SMTP id 98e67ed59e1d1-36bbcfd8de4mr3965602a91.16.1780067297895; Fri, 29 May 2026 08:08:17 -0700 (PDT) Reply-To: Sean Christopherson Date: Fri, 29 May 2026 08:08:14 -0700 In-Reply-To: <20260529144435.704127-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260529144435.704127-1-seanjc@google.com> X-Mailer: git-send-email 2.54.0.823.g6e5bcc1fc9-goog Message-ID: <20260529150814.714658-1-seanjc@google.com> Subject: [PATCH v4 39/47] timekeeping: Resume clocksources before reading persistent clock From: Sean Christopherson To: Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Kiryl Shutsemau , Sean Christopherson , "K . Y . Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Ajay Kaher , Alexey Makhalov , Jan Kiszka , Andy Lutomirski , Peter Zijlstra , Juergen Gross , Daniel Lezcano , John Stultz Cc: "H . Peter Anvin" , Rick Edgecombe , Vitaly Kuznetsov , Broadcom internal kernel review list , Boris Ostrovsky , Stephen Boyd , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, linux-hyperv@vger.kernel.org, virtualization@lists.linux.dev, xen-devel@lists.xenproject.org, David Woodhouse , Tom Lendacky , Nikunj A Dadhania , David Woodhouse , Michael Kelley , Thomas Gleixner Content-Type: text/plain; charset="UTF-8" When resuming timekeeping after suspend, restore clocksources prior to reading the persistent clock. Paravirt clocks, e.g. kvmclock, tie the validity of a PV persistent clock to a clocksource, i.e. reading the PV persistent clock will return garbage if the underlying PV clocksource hasn't been enabled. The flaw has gone unnoticed because kvmclock is a mess and uses its own suspend/resume hooks instead of the clocksource suspend/resume hooks, which happens to work by sheer dumb luck (the kvmclock resume hook runs before timekeeping_resume()). Note, there is no evidence that any clocksource supported by the kernel depends on a persistent clock. Reviewed-by: Thomas Gleixner Reviewed-by: David Woodhouse Signed-off-by: Sean Christopherson --- kernel/time/timekeeping.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index c493a4010305..26f3291a814d 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -2098,11 +2098,16 @@ void timekeeping_resume(void) u64 cycle_now, nsec; unsigned long flags; - read_persistent_clock64(&ts_new); - clockevents_resume(); clocksource_resume(); + /* + * Read persistent time after clocksources have been resumed. Paravirt + * clocks have a nasty habit of piggybacking a persistent clock on a + * system clock, and may return garbage if the system clock is suspended. + */ + read_persistent_clock64(&ts_new); + raw_spin_lock_irqsave(&tk_core.lock, flags); /* -- 2.54.0.823.g6e5bcc1fc9-goog