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 485153AFAED for ; Mon, 10 Aug 2026 09:23:31 +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=1786353814; cv=none; b=qfLF/sCFA50/fbNTH46LpWkMOKnZqgi/2UGBzPTfMSBi0asxkGCIq/T+KqY1SABC+DnioBPKq+d83ZWknXFmVKs+VDpRFb3e0Y42KQjFakqUY/Le7CjzsqCyPRoVAFHUABjUGqBlywaqQoGZhE7o8duuVxpqQ6ThwQol40qB7FY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786353814; c=relaxed/simple; bh=iU77mcjkQDg2G6pbzV+kR2o67ncJLSaEVuMAhfqDt6U=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=q8e0wCcIxRzzVd//Tuu3PdLJtG6z2RXP1tUS+52ynDzYfadj5ZcZTDYkbrIkbXZGnuqBrZCaOv3iERUqK2DEwazBKrhErH8KpkGEt6b0Wa4X6IoLmNo6HhRw8ihAlLlDWoNiIc6t3tt/FeXQhR7oyxCikZKRYs5QfmXmSSvSKpc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Zi/LGmcu; 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=pass smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Zi/LGmcu" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=uNDbFtmjo9CMFVo4IK8OY08Ua0RUd9s0FG/DNegI+30=; b=Zi/LGmcuM0I3p921elI6ZBvp1X caWBunwQRIUy7aM4MoLwms3QT+soqUCJ9Vxfnx/ZvBJA0kThGbYosyBgb5348BGTJqH/xqXjO+7Rd N96ohvtzJ92cT0xRrNhOl+he9WMJ7r7vFNsiCzTyqu8XMYEOfayYiU9LGQ4ODGmbC7qzGuxwFt+BY 0r+QTnpz87n1zmP9Dv2tBZ6bHkse4SYDOe9j9NBx/u6sO2rO1mfXlej9WGGITFCKc4fKp1U4mzH1R alPaQCn5hk3zCRQJqiozh2y7K6SXD5evBtZPlXff/TA4GpsFa6Ep8kb1M5QLJ6aT/5EQ68iArbmaA gDfqoH3g==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.99.2 #2 (Red Hat Linux)) id 1wtMED-0000000Deuj-132r; Mon, 10 Aug 2026 09:23:29 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 8107C300244; Mon, 10 Aug 2026 11:23:28 +0200 (CEST) Date: Mon, 10 Aug 2026 11:23:28 +0200 From: Peter Zijlstra To: Sergey Senozhatsky Cc: Thomas Gleixner , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: x86: missing FRED #PF event data? Message-ID: <20260810092328.GH1642880@noisy.programming.kicks-ass.net> References: <20260810090347.GS48970@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Aug 10, 2026 at 06:09:43PM +0900, Sergey Senozhatsky wrote: > On (26/08/10 11:03), Peter Zijlstra wrote: > > > > > and got the following while running my tests (and well, we don't crash > > > > > anymore): > > > > > > > > > > [ 254.040223] :: fixed up address to ffff9c4d64af4000 [[fred: 0 cr2: ffff9c4d64af4000]] > > > > > ... > > > > > [ 1821.904563] :: fixed up address to ffff9c4e9dd0a000 [[fred: 0 cr2: ffff9c4e9dd0a000]] > > > > > > > > > > Does any of this make sense to you? > > > > > > > > I think the explanation is some pKVM shenanigans. Sorry for the noise. > > > > > > No, I think we are back at square one. I thought that maybe pKVM > > > was disabling FRED and that was causing issues. But I actually see > > > that both cpu_feature_enabled(X86_FEATURE_FRED) and (cr4 & X86_CR4_FRED) > > > claim FRED is enabled, yet fred #PF data is 0 while CR2 holds the correct > > > address. > > > > Can you reproduce on real hardware? I mean, you were babbling about pKVM > > (whatever that is), so I'm thinking you're on some dodgy virt thing. > > > > Not that I have any actual FRED hardware to test anything on :/ > > It's an actual H/W, a laptop (Intel(R) Core(TM) Ultra 7 355 powered), > I was babbling about pKVM because it seems that the best way to > reproduce is to launch a VM, yet the crash is happening on the host > side. Urg, ok, lets wait for hpa to wake up. He's the one that knows most about FRED.