From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 F0F63331234 for ; Mon, 17 Nov 2025 19:39:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763408361; cv=none; b=aKWKrK7iryJiAitHeHcij15VINShjB23ZA+7wSLixVIsacD8FAC9RhtIgYGE1IZQ1J/PWe5pV1PvLBnaI4uSMy8La+8xkKlwQ56fZePZ38HoVyq7brNga3xOQZMnLjAT7jeYIfzqSpyhhu6ndp89WPWVvxfum1PHVhbRPmDdB3I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763408361; c=relaxed/simple; bh=29tvvpCD+qGhy6fyzBHvXQq3vnNQo5h2KbSk1H50wjQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Ny5hujc3EF60uVu06IAenVw+j3cejgTZI8vojZv1hsakQTmA+fMG6mYsYMMhfcD6nAOp4f6CANH6+b+wPJXU7S/GjTXihDEIy3TNiz6H2Fu0b5PC8fWmWGzuZkanAFtJAFNIjBMY48he4nSp0NocGoOS4jqSIdbM2IBAUPLQcwc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=ZCFSJUVS; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=geEMxhT6; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ZCFSJUVS"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="geEMxhT6" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1763408358; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=K36xwmi8QzbZYxYPWk/InVL39QSCuciwcJPm/PdZki0=; b=ZCFSJUVSbyJXAwvpQbj2ICnDq67ZLKaOZAo7XSuEyClw0JS8M1YXfCSq455RUUWX/eym1x n0bd6bu3OUhs8rKM2+xoDThSq31zQfkfv2iN5oFQ7ENSjin1nH8VVJv92OmWheXYDRwmeV ralRcpSTxanDyjyKeOSE0/ZswoyuxVE= Received: from mail-qv1-f69.google.com (mail-qv1-f69.google.com [209.85.219.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-336-k_JuVb1pO0mALKO1nDEbsw-1; Mon, 17 Nov 2025 14:39:11 -0500 X-MC-Unique: k_JuVb1pO0mALKO1nDEbsw-1 X-Mimecast-MFC-AGG-ID: k_JuVb1pO0mALKO1nDEbsw_1763408351 Received: by mail-qv1-f69.google.com with SMTP id 6a1803df08f44-880501dcc67so160309706d6.3 for ; Mon, 17 Nov 2025 11:39:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1763408351; x=1764013151; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=K36xwmi8QzbZYxYPWk/InVL39QSCuciwcJPm/PdZki0=; b=geEMxhT6OC9PKaHjaYOkGjoxff60Ds5axjcfCP5UxrqV/LYE60W8sffaN3UKg0mRWZ mB7a4hNuIdAenpAvNxobzQ0/fo7qabyj8K73rHE2xwK4vDz+rq1ri67wV81EYSyca40v RmKMKKp+c/rhK4tUuA4qIPTGcAwv2oueXK/cGCujbsY3vjWrRUBR0tyvBPn+YBPFoWrH dfQ4DVsHcGp9X0/hQ0OZT4SJ0DRBmwURbdPQEFnUuef1ldAU+9wLRDyF71rr7k3zbTla Zbi4HApC5h8+whMNHHQSR8qbrTvJWPiRYAIuFjP2GTtLgpOVWmh3/kdcoA/fMOZ+s5Ph gZRg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1763408351; x=1764013151; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=K36xwmi8QzbZYxYPWk/InVL39QSCuciwcJPm/PdZki0=; b=s6tg9mEEef1QicL7RzDwHkl5eVaWOzB9+E3WUk3f10P7A16bhCzWzNeP+GIq1HnT6m KJBA+yBFI5gXRzS920exzwsCvsYOMT7GkPb38VO368ZcCNSq0k73DMKMCGAsSmOP8aWf 4pfDnOIA+y5hjjYJy3OXFhc4A4fYBr1XzGssJ02JjbxrahqxmRJAq73c0xu9O79Rimt3 UA/FU7Sceujr+02m+mO9wE90LM/HNek1v+oaqRPy0seytZKpdYTDo5axt0psKY7+6Xmm IBk+A4wm+1nCWxa9y90xYKXcpGS1mSesBPnoOV0oh1c0v17GB81Obz/qS7mOg+t191u3 nC3A== X-Forwarded-Encrypted: i=1; AJvYcCX/RahxLKbZus091irBlPljxr5h5Z0JPg5rTEKt5Hc8PLA4/XLaRmOIl4JSz6Vbun3d5KSoRs/GR7mMcs+W+Pg=@vger.kernel.org X-Gm-Message-State: AOJu0YzeFzXmeMUvp1MjQ+qbJ33wJcXuhHmgzsLt+C7e8L94Ova8k3Bs H8oN2l/XeS9igaGR3Q7ovq6Xa1SAE5ZOzSK0EAnbM6BGWyv+30wcKCuCqswJ7iaMqJBglIgv3T8 1R6/e4V9jcRKf+Mqyoqirmhia/TN2XDoRWwQxAKBi7EEYhrw45LQnOjFMsMur9+zmIC1fdg== X-Gm-Gg: ASbGnctqAOtvvENZOjTaiddFIbGmvGhbFag9SRIlZBvQ1zXP3FQvoTG+peuBSzoE+sC KVr/vYqgMEANBIJgimDLOTnyFzkc1l1joIKqo0eUnXQLi2+TDeSlQSMUU4Anr+BFs3KijpZPz5p 6A7oi6ozHf/qhdqSfoVFBTSLbb21W7VmBAOX3U7t9BFPI71XfKhUPA7GADSU0rH49zNa3s1W0xD JCtjWOK74j6WI5nY+0O5bODWJu/9UWY+ZFShJI3NCEgrh+LSgvNQKwGLkM6uuHyW8EZTEJ4NYQs gc5ofgffx84ZcZXShvlKraAdp/ApKgYC+R/0BNNUFRLt4EVm3oO5zhJztRSD4PD5jNKV33jVoA7 bhg== X-Received: by 2002:a05:6214:c28:b0:802:a79d:3132 with SMTP id 6a1803df08f44-8829267c1c6mr192021106d6.47.1763408351060; Mon, 17 Nov 2025 11:39:11 -0800 (PST) X-Google-Smtp-Source: AGHT+IGdehJMTGS035Eb/OzG7cG5rRd+07wCiKuKE4YM34HxqUOjomc6mUNHGC8OLoiF8h+l5gT9Zw== X-Received: by 2002:a05:6214:c28:b0:802:a79d:3132 with SMTP id 6a1803df08f44-8829267c1c6mr192020686d6.47.1763408350619; Mon, 17 Nov 2025 11:39:10 -0800 (PST) Received: from x1.local ([142.188.210.50]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8828658ae99sm97099586d6.48.2025.11.17.11.39.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Nov 2025 11:39:10 -0800 (PST) Date: Mon, 17 Nov 2025 14:39:06 -0500 From: Peter Xu To: Nikita Kalyazin Cc: Mike Rapoport , linux-mm@kvack.org, Andrea Arcangeli , Andrew Morton , Baolin Wang , David Hildenbrand , Hugh Dickins , "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Paolo Bonzini , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [RFC PATCH 0/4] mm, kvm: add guest_memfd support for uffd minor faults Message-ID: References: <20251117114631.2029447-1-rppt@kernel.org> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On Mon, Nov 17, 2025 at 05:55:46PM +0000, Nikita Kalyazin wrote: > In our use case, Firecracker snapshot-restore using UFFD [1], we will use > UFFD minor/continue to respond to guest_memfd faults in user mappings > primarily due to VMM accesses that are required for PV (virtio) device > emulation and also KVM accesses when decoding MMIO operations on x86. I'm curious if firecracker plans to support live snapshot save. When with something like ioctls_supported flags, guest-memfd can declare support for wr-protect support easily too, and synchronous userfaultfd wr-protect traps will be an efficient way to do live save. I'm guessing it's not an immediate demand now or it would have been asked already supporting both MINOR and WP, but I just want to raise this question. Qemu already supports live snapshot save, so it'll always be good gmem can also support wp at some point, but it can be done later too. Thanks, -- Peter Xu