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 4AA5D356767 for ; Wed, 24 Jun 2026 17:01:25 +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=1782320486; cv=none; b=bKtwzlKYWDeEVrz/2IRJRSM64JHznh5556eGQ3W/nXCECiP9wmA7cFAGji5HOtjOq9YQlWW3H3bSnyn8YUHhEz+ZU99Znhi8DCgDVtv+yMyIreYzeMRb9wFW4/igLOp0t4T9SzOe8d3F1zn/Q97i2NUYt7hVQs8MbOVuXqRu7Es= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782320486; c=relaxed/simple; bh=hXT+eybuvhiG4/K2l6t7f2dd3GljuDBbH8uGde2JbnE=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=EZNShwR+28yU7VqaRhZ803opLcDz0zdhXcR43cKVMUn+MUzn+fsq94o4WeH04hHHij53HVTpZM/UtktA47ZaAjad+PlaYvLgR956v/TkzoyTLcOweOyj2v62l8R5vY19Q+UOQSWWth0Zz5KOlpwlZgSH5yf/THtdNsp25vluLOU= 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=aT6B70Ue; 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="aT6B70Ue" Received: by mail-pf1-f201.google.com with SMTP id d2e1a72fcca58-8453031c57cso2000169b3a.0 for ; Wed, 24 Jun 2026 10:01:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1782320485; x=1782925285; 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=ISY2wbCcsFGmwP11+MNFOlIY+gG7N5avT6t+DVDnEh8=; b=aT6B70UeQi1vhLwWIHICEyqAfUAAREJKRiIgtpkV+Yo3kcrwdppToFiPpaqGgWSe/P 5EiS5+p1013mCbIEYRcqbbj5zDRwJqqsrKPJDXlbbkNoV9Ero30iwoJMkc1ZvGslC8Tg D2+Ia+JK5v2Kj1vw5RAsPYlKlk1I5UJSuQNTdP1fbaJNqn2OD0FnUnkjU1jmgEX7a3vR nn2MQXS3HP9y66yUj+w2HEEe/KdVKjfu1tMjLmbt0zxyVhSbLWIw9EdVIIwE5O9uliWD gZxejg5kAomk+aK27w6cqdP7G1EjYG+Jl/dt6OsS7sH0cGao42WKPIUDJ6OWTQY2KCl3 NS7A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1782320485; x=1782925285; 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=ISY2wbCcsFGmwP11+MNFOlIY+gG7N5avT6t+DVDnEh8=; b=nrGzpsG1IkhWEROaUQ6mhiE0ZTrmIWxaQASZda2/yaGyEjpKBhNQSJTLsvC90d5iGz mcvLhxXDh5LsT6oTqSXnr3jIc+DaXy/vAEyyY1o9c27IRNMV2WllZByL2G553DZ/98ye iNk9LDVwtlGcHwPh/q1SkvJcW6N6P/VLcg2xq7mkXzVA+/fdwI1LH9H01XkJdjoNCgBI VHKS0pUHV0hlDL1PkX+UBauUwesLHBteNk69oT+B2dL2P3ggVyZ+9tatrkXcUoBEubd1 zGCp0OU9McgDGbRHgBA094InO6k7iCVKSwxi+EbjxnxBaQ07zT87XP562jhcX3al5G8u dPrw== X-Forwarded-Encrypted: i=1; AFNElJ+Fwca1XQaaCcqnIg4YyoUN23pC+DvMMatoYiIN92+hjO1Dim5dg9MJ4o4mn5dGq/r6kDNHHKm6BhhDSnCxa3s=@vger.kernel.org X-Gm-Message-State: AOJu0YwQcP174YZbjyI9l0BzXOnugpaSBZ8THynalk8Fv9w9W1AuIbtt ea0ohvw+EdUF2SQKlsru6HP5JE1g9pjNvzbVaoWPHNU3ydPgW6Xl1Bx4GmH3NAXKNglqvi9F5+h v8AQFgw== X-Received: from pfnp26.prod.google.com ([2002:aa7:861a:0:b0:83a:68c:e1c6]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:aa7:88ca:0:b0:827:2a07:231d with SMTP id d2e1a72fcca58-845a26d1fe1mr5396846b3a.17.1782320483693; Wed, 24 Jun 2026 10:01:23 -0700 (PDT) Date: Wed, 24 Jun 2026 10:01:23 -0700 In-Reply-To: <6fc7f450-6d0a-494d-b295-297e4703148d@linux.intel.com> Precedence: bulk X-Mailing-List: linux-kselftest@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> <6fc7f450-6d0a-494d-b295-297e4703148d@linux.intel.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: Binbin Wu Cc: ackerleytng@google.com, aik@amd.com, andrew.jones@linux.dev, 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 Tue, Jun 23, 2026, Binbin Wu wrote: > On 6/19/2026 8:31 AM, Ackerley Tng via B4 Relay wrote: > > @@ -606,12 +608,20 @@ static bool kvm_gmem_is_safe_for_conversion(struct inode *inode, pgoff_t start, > > next = start; > > while (safe && filemap_get_folios(mapping, &next, last, &fbatch)) { > > > > - for (i = 0; i < folio_batch_count(&fbatch); ++i) { > > + for (i = 0; i < folio_batch_count(&fbatch);) { > > struct folio *folio = fbatch.folios[i]; > > > > - if (folio_ref_count(folio) != > > - folio_nr_pages(folio) + filemap_get_folios_refcount) { > > - safe = false; > > + safe = (folio_ref_count(folio) == > > + folio_nr_pages(folio) + > > + filemap_get_folios_refcount); > > + > > + if (safe) { > > + ++i; > > + } else if (folio_may_be_lru_cached(folio) && > > + !lru_drained) { > > + lru_add_drain_all(); > > It seems unprivileged userspace is able to trigger lru_add_drain_all() repeatedly > by invoking KVM_SET_MEMORY_ATTRIBUTES2 in a loop, which could lead to DoS risk? FIW, if there's a risk, then AFAICT fadvise() and memfd's F_ADD_SEALS already have the same risk.