From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 E21973FFF8C for ; Fri, 17 Jul 2026 13:44:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784295882; cv=none; b=tS7GwDdhFj272A+NowWb2KURJmTAzUPooDauvvsE3FYW+/+fuaUYl+r7aGfLsVj13ydTUMHpUpQtqKh6GPQfNilGs3wxZ9d5cEx3MtQsDY42dfcJrUb2fU/MQLZsrjVOXjvsU7IZ6MWPILkGjjztMEhbkAr+L9sPT9ZAmh0ifsI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784295882; c=relaxed/simple; bh=dwVJh7myX7EoZanWd9ur5jP8Ylzyepte5ccocb4xKz0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=YtgB7vVNj4qeKtQKgQyFN46uTSBZrFAwPvnezoHXnpiY1I7otlGUvvCXLhhhkzUzK6rn+YKHdxiZo9gRjk9VqlIpgAJRu4G7ftmELMxFJ8TfbaSuVWnBNX/vEG119xuR7WrGZzvj5k76ro08V/e8MQpdBOO0kyGzzrPBsjabbnU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=1ORy/X/2; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="1ORy/X/2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6361D1F000E9; Fri, 17 Jul 2026 13:44:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784295879; bh=oMoCFomhpwJLhR4rcWOfMowxTHT4iCa5qNB8wbw6F40=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=1ORy/X/2+2FJHX6K2xbwq3aPBtwMWwZnhJiG74+xeIUutTlD3L7KQ7Cg1JeQIqUUr XTiqC7TkJfbb59DZiuxYJ29We1aKRWWCGj6km05HlgOj6vp59zbKsne/HpgfypECcW YuBCjK3xvm8eP86SQ6oj66BpYCRz3PFP3NhtjD4k= Date: Fri, 17 Jul 2026 15:44:32 +0200 From: Greg KH To: Rishi Chhibber Cc: arnd@arndb.de, linux-kernel@vger.kernel.org, ajay.kaher@broadcom.com, alexey.makhalov@broadcom.com, vamsi-krishna.brahmajosyula@broadcom.com, yin.ding@broadcom.com, tapas.kundu@broadcom.com Subject: Re: [PATCH v2] misc: vmw_zerocopy: Add VMware zero-copy buffer sharing driver Message-ID: <2026071748-poking-cable-8f61@gregkh> References: <20260617203125.397427-1-rishi.chhibber@broadcom.com> <20260618181034.1483738-1-rishi.chhibber@broadcom.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260618181034.1483738-1-rishi.chhibber@broadcom.com> On Thu, Jun 18, 2026 at 11:10:34AM -0700, Rishi Chhibber wrote: > This driver implements a misc character device (/dev/vmw_zc) that allows > guest userspace applications to share pinned memory buffers with a > VMware hypervisor-side peer using the VMCI datagram interface. > > The driver pins user pages via get_user_pages_fast(), transmits their > physical page frame numbers to the hypervisor peer over VMCI, and avoids > an intermediate copy between the guest workload VM and the hypervisor. > > The hypervisor-side peer for this interface only speaks VMCI; there is no > virtio backend implemented on the VMware host for it. The closest > existing upstream transport, vsock (virtio-vsock), provides a socket > bytestream/datagram abstraction and does not expose a way to hand a set > of pinned guest page frame numbers to the host for true zero-copy > access; it would still require copying the payload through the socket. > This driver's purpose is specifically to pin guest pages and pass their > PFNs to the host so the payload is never copied. It also supports > bundling multiple buffers in a single request, which is required for the > all-or-none semantics of page-level zero-copy transfers. Ah, wait, i see why this is needed. Why not just add the needed functionality to virtio instead? Surely other hypervisors (like hyperv) need/want to do this same thing? How do they do it? Through custom drivers like this or through something else? thanks, greg k-h