From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="gpQ586ja" Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EBDE0101 for ; Mon, 4 Dec 2023 21:26:02 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1701753962; 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=UItdnX8ajj27d5Qso73kxc+PaX4o0omDbnZKQK9rTcs=; b=gpQ586jaC230LhcJLHPoJ1GX7hNfSuAKPXQksdGsLd6JGb9sORGwCOfO97w1sISBFk8aFU kkJkNlhuIX5WIw8pzEqF5Aztkvij5EbjjsMYkIBWAEflrxEFM2oPRjU+pcwWvK3SrgKyJW LzAZJkR0/azujvMgGgtYzjCEfYs7QyU= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-630-VYnt0zC1PLC1jjSTgEIXlA-1; Tue, 05 Dec 2023 00:25:56 -0500 X-MC-Unique: VYnt0zC1PLC1jjSTgEIXlA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 700411C068DE; Tue, 5 Dec 2023 05:25:55 +0000 (UTC) Received: from fedora (unknown [10.72.120.3]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1F6671C060AF; Tue, 5 Dec 2023 05:25:48 +0000 (UTC) Date: Tue, 5 Dec 2023 13:25:44 +0800 From: Ming Lei To: Keith Busch Cc: Jeff Moyer , Keith Busch , linux-nvme@lists.infradead.org, io-uring@vger.kernel.org, axboe@kernel.dk, hch@lst.de, sagi@grimberg.me, asml.silence@gmail.com, linux-security-module@vger.kernel.org, Kanchan Joshi Subject: Re: [PATCH 1/2] iouring: one capable call per iouring instance Message-ID: References: <20231204175342.3418422-1-kbusch@meta.com> Precedence: bulk X-Mailing-List: io-uring@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: X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 On Mon, Dec 04, 2023 at 09:31:21PM -0700, Keith Busch wrote: > On Tue, Dec 05, 2023 at 12:14:22PM +0800, Ming Lei wrote: > > On Mon, Dec 04, 2023 at 11:57:55AM -0700, Keith Busch wrote: > > > On Mon, Dec 04, 2023 at 01:40:58PM -0500, Jeff Moyer wrote: > > > > I added a CC: linux-security-module@vger > > > > Keith Busch writes: > > > > > From: Keith Busch > > > > > > > > > > The uring_cmd operation is often used for privileged actions, so drivers > > > > > subscribing to this interface check capable() for each command. The > > > > > capable() function is not fast path friendly for many kernel configs, > > > > > and this can really harm performance. Stash the capable sys admin > > > > > attribute in the io_uring context and set a new issue_flag for the > > > > > uring_cmd interface. > > > > > > > > I have a few questions. What privileged actions are performance > > > > sensitive? I would hope that anything requiring privileges would not > > > > be in a fast path (but clearly that's not the case). > > > > > > Protocol specifics that don't have a generic equivalent. For example, > > > NVMe FDP is reachable only through the uring_cmd and ioctl interfaces, > > > but you use it like normal reads and writes so has to be as fast as the > > > generic interfaces. > > > > But normal read/write pt command doesn't require ADMIN any more since > > commit 855b7717f44b ("nvme: fine-granular CAP_SYS_ADMIN for nvme io commands"), > > why do you have to pay the cost of checking capable(CAP_SYS_ADMIN)? > > Good question. The "capable" check had always been first so even with > the relaxed permissions, it was still paying the price. I have changed > that order in commit staged here (not yet upstream): > > http://git.infradead.org/nvme.git/commitdiff/7be866b1cf0bf1dfa74480fe8097daeceda68622 With this change, I guess you shouldn't see the following big gap, right? > Before: 970k IOPs > After: 1750k IOPs > > Note that only prevents the costly capable() check if the inexpensive > checks could make a determination. That's still not solving the problem > long term since we aim for forward compatibility where we have no idea > which opcodes, admin identifications, or vendor specifics could be > deemed "safe" for non-root users in the future, so those conditions > would always fall back to the more expensive check that this patch was > trying to mitigate for admin processes. Not sure I get the idea, it is related with nvme's permission model for user pt command, and: 1) it should be always checked in entry of nvme user pt command 2) only the following two types of commands require ADMIN, per commit 855b7717f44b ("nvme: fine-granular CAP_SYS_ADMIN for nvme io commands") - any admin-cmd is not allowed - vendor-specific and fabric commmand are not allowed Can you provide more details why the expensive check can't be avoided for fast read/write user IO commands? Thanks, Ming