From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f202.google.com (mail-pl1-f202.google.com [209.85.214.202]) (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 66F9C30100E for ; Wed, 24 Jun 2026 16:57:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782320227; cv=none; b=hDJ32Ysf0xIJJW7YmU2DUm41rKXMT297zZnTYxsqD8E9B1tF5Du1ClPioeURzJKZwYpeEQbe9QDlqFs65mcduo2c5I1S+PEBt3RrefpcNE2CVVMOgL95OrSYC0BUfmBvYDJfhIBTczBw1eJmKWq2ve98rqCLi7UQVkEuEXAw0Lg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782320227; c=relaxed/simple; bh=sFclBlGuLlklutyWalxOxdLRxtPJWxF7xb2dfh79PCc=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=q9qW3TpZN3Qb4rzKoLac6BfGYu6D8Kws+14cKYD3+cHiik3av6VhtmiywmeLnkqV8ealhGcaxxn9+4MTWX5XKogNDtsbHWdub8n9rMDt/GKzc6/FxcGlU/iz4vZpEeOFPFK0aLsENS/IWd7r+WL0QGnqKVSeaeZdUzROC/viChA= 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=bvJxEX3r; arc=none smtp.client-ip=209.85.214.202 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="bvJxEX3r" Received: by mail-pl1-f202.google.com with SMTP id d9443c01a7336-2c0d0516ad7so8395745ad.0 for ; Wed, 24 Jun 2026 09:57:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1782320226; x=1782925026; 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=bTiRAq90VFPvdthoswICGCbbk82NFtmBH/qctXPK1uM=; b=bvJxEX3rsk8IBE8FBs+jN29a+YeGR3JEDndKlMnuwYxHyJeTAO5qxR4Z1TjsSyaM2Y baknumWOVQBnwfnzwfeNHNIOdr2/J/ZcfMzNU+XOEXx0rThPrSQ00W5DDfd7iLom7fx8 zq7udvudFJ7BGPqnbxkZg4rFq49YCYlLtfWY+NKZxUpTaU34XLaMPxThLQQ1r4e/isJQ UOox1nyS7dd8DycpoKRIPGOYhZR/y1jutm52zreGNncrofsIVzvOmJATEmaWKgrR8yWX Qpj9AfGMyziKgSfVeRBzsGnaH4uWKTxus/U/EC62RdpksdCAlG8Vo14jIymdxbnYN3e4 W2bA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1782320226; x=1782925026; 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=bTiRAq90VFPvdthoswICGCbbk82NFtmBH/qctXPK1uM=; b=a1dMPU6EwCrKlx8AzP3i0sw0ak05CJZ8TePMixyrFrggfmMWkep7V2fMwFSHJVF8pH q6YKcauMVBzHZf5B12kUUtyHN1h+4dsRQBtfO4BuS3sbhYvI9OL+viAUzyKS74d+ywRK BuW+jqXtjtQBypJFUhXUwVqFSUcgHNMMqv8NWPXR+B3peq1qrNrVDVWi4Ud5n2mk2Iio LnfYYsIxRQK/gLGQ+nk4h39P4n1RluHf7Vpwh4hlP7DQdVuCViOvkq8S4KNfti4CVO/U eG7kjCIkFgQkH52pOZLpoasimP2KG26QBhTfwvFdfBpsBl8/KCjdjudkildv5VB5hiOm l7FQ== X-Forwarded-Encrypted: i=1; AHgh+RqlrM72ATUuzbpn3l6hLsHMz9PGxrVcjoRgXuhCUkhOwGcqpYyLNbYSyk7r/GNC+S3Cl/v6Rte+eVILdTWxPB02BmI=@vger.kernel.org X-Gm-Message-State: AOJu0YxriuiW7LZdAP/0Mh7fgmA0VywtyqcDMdS848aJ2ZkhjB20aK4R OivkjWok9gc03MyR/lhhKnFdJOmFG2AYeEh7V4ql9Ok22V9tCTaK6tGkjm5fetbGXxXdPf2B/E/ /64Nu/g== X-Received: from plpn21.prod.google.com ([2002:a17:902:9695:b0:2c6:b814:535b]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:fd47:b0:2c0:b081:84b1 with SMTP id d9443c01a7336-2c7e1464d1amr26763135ad.10.1782320224855; Wed, 24 Jun 2026 09:57:04 -0700 (PDT) Date: Wed, 24 Jun 2026 09:57:04 -0700 In-Reply-To: <20260618-gmem-inplace-conversion-v8-18-9d2959357853@google.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260618-gmem-inplace-conversion-v8-0-9d2959357853@google.com> <20260618-gmem-inplace-conversion-v8-18-9d2959357853@google.com> Message-ID: Subject: Re: [PATCH v8 18/46] KVM: guest_memfd: Handle lru_add fbatch refcounts during conversion safety check From: Sean Christopherson To: Ackerley Tng Cc: aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, david@kernel.org, jmattson@google.com, jthoughton@google.com, michael.roth@amd.com, oupton@kernel.org, pankaj.gupta@amd.com, qperret@google.com, rick.p.edgecombe@intel.com, rientjes@google.com, shivankg@amd.com, steven.price@arm.com, tabba@google.com, willy@infradead.org, wyihan@google.com, yan.y.zhao@intel.com, forkloop@google.com, pratyush@kernel.org, suzuki.poulose@arm.com, aneesh.kumar@kernel.org, liam@infradead.org, Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Shuah Khan , Shuah Khan , Vishal Annapurve , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Baoquan He , Jason Gunthorpe , Vlastimil Babka , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev Content-Type: text/plain; charset="us-ascii" On Thu, Jun 18, 2026, Ackerley Tng wrote: > When checking if a guest_memfd folio is safe for conversion, its refcount > is examined. A folio may be present in a per-CPU lru_add fbatch, which > temporarily increases its refcount. Under what circumstances does this happen, and what alternatives are there for userspace to work around the issue?