From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f201.google.com (mail-pf1-f201.google.com [209.85.210.201]) (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 0247F3B19A1 for ; Wed, 8 Apr 2026 16:34:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775666043; cv=none; b=uw8kgeP7RW0eh20B163RJLEVnXWSyO8FW7qPO2BEf6kiCeW5cEyMQYQfSjCcHTCQU/+skay5QZrsV1tqTn4dyGTj/Q80jcTbHiI0tC6NWs5Ok9DGzzg1ectcS5C+1uenXzPltf7Nsmgw1AOHd9rptSI61o/Nva+s3LOTxrntrWA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775666043; c=relaxed/simple; bh=vzY/tSccfUbpoIfIZ8q9iKRIGKC2EBwbVZfImdNkwfg=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=uqBwPTnfQb0NRyFX4PwUV3LJDJsFpxuielXXrQIRq7J8J5+1CpmCODK1PPZBqx1FVFoTawzoC1rK9dtgRhUzCW3CAVoT+m76uRiR5z2jsi0JrygZ1NPEBkU0pUjiMWLnxJltPi9qbqXgVNs2CUQqNo0DnO0WDREpS0vKVrSpzWQ= 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=YNbTRLhM; arc=none smtp.client-ip=209.85.210.201 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="YNbTRLhM" Received: by mail-pf1-f201.google.com with SMTP id d2e1a72fcca58-82cd9fa609aso3924936b3a.3 for ; Wed, 08 Apr 2026 09:34:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1775666041; x=1776270841; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=jRZXONeJDxUiLh0aG70nVlhtcf1yGjwZiaYa9FOO/1Y=; b=YNbTRLhMZICWFhkyNgHz4XJh+VUJpOK5CZnMroeJws2utNbzPVbWWNhdeWPDuOFJpJ iNxhNk72K0fiAgbkD0ZYjBWvl/EgmXIKvIu0LIwLG8IDi3ofGlT00AoCmaxTuSerAHYE S1w0+SjRosRzBGRULK88eOwBXZNq/FQ8fsnE3jmMlC7iOIDtXnZ+rHJvdR+3INtVviJZ Rp3mbSDCbCOXZlwtl2cLBlUwy5NoKf5Tzj14DNJkkd/+FJI74ANY/lr7BAY1noV4140t JcaSA4KxxF6ZOpjIYkn3cM+BvUf43I4Pd1Ws5t6ifDqORXpzxkv0YQk4gbRFnf1w+dgp 0vmQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1775666041; x=1776270841; h=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=jRZXONeJDxUiLh0aG70nVlhtcf1yGjwZiaYa9FOO/1Y=; b=W0d3zgqOcH2kMTTH3qWbDdyIM8Yp7o09NC2mKVVZcE9nvsw7HlQ8Nx3JkNhGUOeAPy bU7egOqNEroyYRDZVA5fW7U+hl5/AvXRRlI6+xh0JX6Joyl+5UZJrK5ZUxcMQ5QcUR1K dUuc1QNf7bx6A+ijO0e8BY+gm1HH1qg/iZKE8EozWxT00B+LmZf4cy1xQ5hogx7783Rr IhyDjdMfjCUmzrcEJjgm6KcQsEdD2cHuvBYCPxwBAM67FW9DTs0nJm8hr/sYrH2eGaZP G2o0fgIDe5KbNE9HoSA6EvI1oTbnna35+Pxdib9pmDQgB01We7pF3oGvpRzyagUrPDPf 9uNQ== X-Forwarded-Encrypted: i=1; AJvYcCX2INEEzzQt0hc16WAP5XO2NBf9iVndPnCWqP/i8oISJPMg1fbNjXNRauvI6S5ayFT5GC9f3Yf5TBvSrbk=@vger.kernel.org X-Gm-Message-State: AOJu0Yz473apN47Bnj0N+siYNhG0a2VEt7xh/lBBpVrpzaUd/ZkU6cZu KxnxnhKN2MvhpZL6IA3BWpeagQg8OLzctVDdbRiV+AGhTZV07qLDnstAk4Xre8f3ukUWIXg8cUV niFaVVw== X-Received: from pgbcx10.prod.google.com ([2002:a05:6a02:220a:b0:c73:faf2:f827]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:7346:b0:39f:a052:39a1 with SMTP id adf61e73a8af0-39fa05241b8mr7282329637.26.1775666041092; Wed, 08 Apr 2026 09:34:01 -0700 (PDT) Date: Wed, 8 Apr 2026 09:33:59 -0700 In-Reply-To: <20260408153650.34484-1-ohyunwoods663@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <202604081418.sean.christopherson@intel.com> <20260408153650.34484-1-ohyunwoods663@gmail.com> Message-ID: Subject: Re: [BUG] KVM: NULL pointer dereference in kvm_tdp_mmu_map under memory pressure From: Sean Christopherson To: punixcorn Cc: pbonzini@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Wed, Apr 08, 2026, punixcorn wrote: > Hi Sean, > > I attempted to trigger your debug patch via fault injection (zeroing > page_private on the allocated sp before it's linked), but the resulting > logs aren't meaningful -- every captured entry shows spte = > 8000000000000000, a non-present SPTE, which doesn't reflect the real > crash scenario where the SPTE is present but page_private returns 0. > So I'm not sending those. Ya, I wouldn't expect synthetic injection to help root cause this. > Natural reproduction is rare and I haven't caught it yet with your patch > applied. How rare is rare? Are we talking hours of runtime? Days? > Given that, what would you recommend as a next step? If it's not too onerous, keep trying to reproduce with that initial debug patch. If the time to repro is several hours (or more), I can try to provide a more elaborate debug patch. > Would lockdep, KASAN, or RCU debugging (CONFIG_PROVE_RCU) be worth enabling > to catch the violation when it happens naturally? Hmm, of those, KASAN has the best chance of being useful. Thought it might make reproducing the bug even more difficult. > Environment: > - CPU: 13th Gen Intel(R) Core(TM) i5-13420H (12) @ 4.60 GHz > - RAM: 16GB (15Gi usable, 16Gi swap) > - OS: Arch Linux > - Kernel: 6.19.10-dirty #1 SMP PREEMPT_DYNAMIC Wed Apr 8 06:08:08 GMT 2026 x86_64 > - /proc/cpuinfo: https://pastebin.com/pwvNYsCu > - .config: https://pastebin.com/z4fVZENs > > The crash occurs while running an Android emulator (QEMU) under host > memory pressure. > > Signed-off-by: punixcorn