From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f197.google.com (mail-pf1-f197.google.com [209.85.210.197]) (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 1F3EA3101D4 for ; Mon, 10 Aug 2026 13:51:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.197 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786369910; cv=none; b=TYzek+9XS+4F/0XYGuVRcZqh1wCaOMbaX2osqsgNb4G1c647E+wen3z1kFvgOU2O6cnXrOiYKRW4A7bDLqovJ3deFFO4Dy8UrSgvX9KbGJavFNkY8zUa/r7+wrZeyO5LpkVZM2nMBa/vy0GJkScpnKHZc3TWnPcXX0w3FZWk5Go= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786369910; c=relaxed/simple; bh=exk8uLRN0Bc33S9yt60+UclTT6d32Uen4mFxGFgbxyQ=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=T/K92IGf0Iy6XLuOkYa3pufwukf2TqaUEptTAalpvF//DJ00CDACqZNBersXq/P4XAElO4+/bSBBGa9VjqAkdNPIXSH6pejajYQFLhi2uu9lamUI9oP2pt0+qy0Idjbu7JZg9/EaEjk3pXde9OUXo6N1exg+AIoOaQyxmXp1JW0= 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=EjuZ+v2Y; arc=none smtp.client-ip=209.85.210.197 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="EjuZ+v2Y" Received: by mail-pf1-f197.google.com with SMTP id d2e1a72fcca58-84f0d3ab2f4so1753010b3a.1 for ; Mon, 10 Aug 2026 06:51:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1786369908; x=1786974708; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=dwEbsrQCY9HWyblIgTS0azUa9TMcbn0+QiKPSQTYxAQ=; b=EjuZ+v2YLXfVcWMkwL/Zz1G8Q5p1SyPe8CiLpTmmSMOgkiAO7O2FnnL2A7HiQfkI9C 4sNXdfMi+0asB26SVUpzBlyiV2K4OZFD7O/aWkle2LFFux6QdW1H7AOr8FimLhlLllch g7rJJbbYrcG3IWS7TXexXzj5MbONQ7a3mvZ5prJDA70hqZuPJZNd1D/PBTKFXKznO4Fz U2sYXyjDiK+d56fZPc1n1xX7Yk5wmuVfGwS+lsvVpFNvT7xRmVy6qRujhu2dIDHJeRxP /Lq/cgG4oD6F1cK15JMm9Pd0x2esp7B/S/vlMzCXuKofyzvfd+xyBYwmAZDqTUYK0amA Xp1A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786369908; x=1786974708; h=content-type: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:content-type; bh=dwEbsrQCY9HWyblIgTS0azUa9TMcbn0+QiKPSQTYxAQ=; b=L7+4hOGiu1SjwWEJIHsb21ffKbMtYKUh7JMb0TgAVpjfCjVgi1lcWjsFmYoiVXvLrI rVraTQk9Zs4u+B/irs9OJL8lNoQKj0X6ni2hFK3I/9+OVsYknnIS4VT+EV5ZxzO7/ye1 ga/ydIknAqgmmretfAGmRNzOGBZoRxPGN2fzRjF3DSGGsQhlgjW1ibGKqDMsmhJnvt1x p4u3YaqmmcBD0oaD2w+C8poyef85hNMQJygYebUKooFBMsUc9xpabMnzzB/hDQGb350Z s1c6g0O+YVHfdN83lLr5v+gKZ2TtEgs1DEIcIJN9tFjDAF2fEKZenc7zZjS+Vj+3nzAq EAeA== X-Forwarded-Encrypted: i=1; AHgh+RpMunqnBcJUTp78V9vCXKyHsZt1jRatJIYQhS1//Qhf8JVBM26kV4LiBBSUJsUzyVtwmoo22Ov107tzh8A=@vger.kernel.org X-Gm-Message-State: AOJu0YwsiLgfPpSu4n4G0oRHBlADt095sdMU2OnnOo3V2+NHK15HC0yC Og8JNIoc7VVtzxwr63z1vfi0BftgBJgvbNHz2ED+0wwYYh7pZ2/dsMVa9Oy/sIve0UZDA/UlOwH wtV8HwA== X-Received: from pfblb23.prod.google.com ([2002:a05:6a00:4f17:b0:848:2ec8:662f]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:4403:b0:842:5b66:3c7f with SMTP id d2e1a72fcca58-84f9c7fc9d9mr1924664b3a.0.1786369907978; Mon, 10 Aug 2026 06:51:47 -0700 (PDT) Date: Mon, 10 Aug 2026 06:51:47 -0700 In-Reply-To: <20260810092328.GH1642880@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 References: <20260810090347.GS48970@noisy.programming.kicks-ass.net> <20260810092328.GH1642880@noisy.programming.kicks-ass.net> Message-ID: Subject: Re: x86: missing FRED #PF event data? From: Sean Christopherson To: Peter Zijlstra Cc: Sergey Senozhatsky , Thomas Gleixner , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Mon, Aug 10, 2026, Peter Zijlstra wrote: > 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. But to Peter's point, babbling about pKVM suggests that you're running out-of-tree patches to enable pKVM on x86, which means this could be a bug somewhere in those out-of-tree patches. And if you're indeed running pKVM, it also probably means the "host" is deprivileged into a VM, which brings KVM and virtualization back into the mix as possible suspects. So, is this happening on a kernel that's fairly close to a vanilla upstream, or is it indeed happening on a pKVM-capable kernel?