From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3E91FC4828D for ; Mon, 5 Feb 2024 12:59:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=JXxAiS5Gf/cqJE/CEevj4751JPq9r1V2TiVxXziAQRA=; b=ILDLlCpCOFm7s8 FClZhd9uZhQIdhH6fF4AWW88G+wKgmD/UGu+F/46G6QeDPdSvEyvRulG2IhCNXbunTRhgsO5tvXA/ yGHXOWBTOEgNGdj7f8i1O28w+vLC13dc3s2n1sBj1C9lXvngCvWut6v8ye8KCTDS49tTo6YN65tom h6X9u45HI0NzmUIDbvyFDD9w0SS3wx0v7QnEGIKF5ZMlkXXe/p2nId12nHGmyV1+v0i3536QmxvYK H+cYAwu/5WJh0GYn0JnSBYbgSFVj8p/Opoe0yp56CPEzm7rPOtv0SfIzhDEJVQ+oF+GXLZPhO+zzR X3g2xTTxd8VQ9ncW5jjw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1rWyZN-00000003KmA-3HrU; Mon, 05 Feb 2024 12:59:29 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1rWyZK-00000003KlK-1Uxv for kexec@lists.infradead.org; Mon, 05 Feb 2024 12:59:27 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1707137963; 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=FpGOJ29CMHAA5hRGumj5ser9f9DDAnohQf19mV7TPfc=; b=GZV3meMgHPKdfdPJr4MA6IjsSShuKxtX4+AI2Z8GAEgR6zZsSrGusD0Qvu413AiMT5av/G IFGa3S2LrS0RWslBcRJdqJpB1PeR6COZJaNQR3CP2h6IThiZBuGDPg+owOCSe9spRdUmHf fAdgoT44ZpMbApq4QwrMyHYqLMQV0CY= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-510-Jgo5-skiN2yhuAa53_qihQ-1; Mon, 05 Feb 2024 07:59:21 -0500 X-MC-Unique: Jgo5-skiN2yhuAa53_qihQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (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 06554862DC0; Mon, 5 Feb 2024 12:59:21 +0000 (UTC) Received: from localhost (unknown [10.72.116.13]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1F4342166B31; Mon, 5 Feb 2024 12:59:19 +0000 (UTC) Date: Mon, 5 Feb 2024 20:59:16 +0800 From: Baoquan He To: "Eric W. Biederman" Cc: "yang.zhang" , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, "yang.zhang" Subject: Re: [PATCH] kexec: should use uchunk for user buffer increasing Message-ID: References: <20240130101802.23850-1-gaoshanliukou@163.com> <871q9r3xl6.fsf@email.froward.int.ebiederm.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <871q9r3xl6.fsf@email.froward.int.ebiederm.org> X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.6 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240205_045926_502367_B9E2E213 X-CRM114-Status: GOOD ( 29.52 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org On 02/05/24 at 06:27am, Eric W. Biederman wrote: > Baoquan He writes: > > > On 01/30/24 at 06:18pm, yang.zhang wrote: > >> From: "yang.zhang" > >> > >> Because of alignment requirement in kexec-tools, there is > >> no problem for user buffer increasing when loading segments. > >> But when coping, the step is uchunk, so we should use uchunk > >> not mchunk. > > > > In theory, ubytes is <= mbytes. So uchunk is always <= mchunk. If ubytes > > is exhausted, while there's still remaining mbytes, then uchunk is 0, > > there's still mchunk stepping forward. If I understand it correctly, > > this is a good catch. Not sure if Eric has comment on this to confirm. > > As far as I can read the code the proposed change is a noop. > > I agree it is more correct to not advance the pointers we read from, > but since we never read from them after that point it does not > matter. > > > > > static int kimage_load_normal_segment(struct kimage *image, > > struct kexec_segment *segment) > > { > > ...... > > > > ptr += maddr & ~PAGE_MASK; > > mchunk = min_t(size_t, mbytes, > > PAGE_SIZE - (maddr & ~PAGE_MASK)); > > uchunk = min(ubytes, mchunk); > > ......} > > If we are going to improve the code for clarity. We probably > want to do something like: > > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c > index d08fc7b5db97..1a8b8ce6bf15 100644 > --- a/kernel/kexec_core.c > +++ b/kernel/kexec_core.c > @@ -800,22 +800,24 @@ static int kimage_load_normal_segment(struct kimage *image, > PAGE_SIZE - (maddr & ~PAGE_MASK)); > uchunk = min(ubytes, mchunk); > > - /* For file based kexec, source pages are in kernel memory */ > - if (image->file_mode) > - memcpy(ptr, kbuf, uchunk); > - else > - result = copy_from_user(ptr, buf, uchunk); > + if (uchunk) { > + /* For file based kexec, source pages are in kernel memory */ > + if (image->file_mode) > + memcpy(ptr, kbuf, uchunk); > + else > + result = copy_from_user(ptr, buf, uchunk); > + ubytes -= uchunk; > + if (image->file_mode) > + kbuf += uchunk; > + else > + buf += uchunk; > + } > kunmap_local(ptr); > if (result) { > result = -EFAULT; > goto out; > } > - ubytes -= uchunk; > maddr += mchunk; > - if (image->file_mode) > - kbuf += mchunk; > - else > - buf += mchunk; > mbytes -= mchunk; > > cond_resched(); > > And make it exceedingly clear that all of the copying and the rest > only happens before uchunk goes to zero. Otherwise we are relying > on a lot of operations becoming noops when uchunk goes to zero. ACK. This makes the code logic much clearer, thanks. _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec