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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 CE2EFC3ABBC for ; Tue, 6 May 2025 16:49:06 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uCLTR-00057i-Qv; Tue, 06 May 2025 12:48:53 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uCLTP-00057R-Op for qemu-devel@nongnu.org; Tue, 06 May 2025 12:48:51 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uCLTO-0003z9-0Q for qemu-devel@nongnu.org; Tue, 06 May 2025 12:48:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1746550128; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2uri6Cd+j223dgdddjZ6llmyapGXFnP5Lsupck775S4=; b=hsrUvTAQRZAT2VNcPCtNWXZCmXhB+Q8S2xrnNT4FUJBLpK9LtaI9nuLNjbCDDSv3dXg4aG 310b/SLm+TkbjSjxXbrs8fwCMWkNi7omEzAy4v2vhAvolSprXitJ8pE0i6xqyJAmge1NLy Pu6CKalR4plZ7uv2qJ4J5hVEQcDGGSg= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-67-q_a5RknIOfmEBM1K1wkICg-1; Tue, 06 May 2025 12:48:45 -0400 X-MC-Unique: q_a5RknIOfmEBM1K1wkICg-1 X-Mimecast-MFC-AGG-ID: q_a5RknIOfmEBM1K1wkICg_1746550124 Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (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 mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id EC6E11954B13; Tue, 6 May 2025 16:48:43 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.127]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7A87F1956094; Tue, 6 May 2025 16:48:42 +0000 (UTC) Date: Tue, 6 May 2025 17:48:39 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Elisha Hollander Cc: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , qemu-devel@nongnu.org Subject: Re: [PATCH v2] util/memfd: allow allocating 0 bytes Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.414, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, May 06, 2025 at 07:41:32PM +0300, Elisha Hollander wrote: > Gave an example for a case where QEMU would try to allocate 0 bytes thus > fail here in the original version of the patch. > > > As I mentioned earlier, let's say you don't initialize the vertical > display end registers, and set the minimum scanline register, the emulation > will then have to allocate some display buffer, but because the vertical > display end is initilized as 0 the buffer will be empty and the program > break. Isn't this an invalid hardware configuration that should be detected in the emulation code, and either force the display end to a minimum value, or trigger an assert ? Patching a bug in a specific HW impl, by changing the qemu_memfd_alloc code feels like it is probably the wrong place to address this. > > I have no idea as for why my emails are getting messed up... :/ > > Have to go now, will try and send it again tomorrow probably... > > On Tue, May 6, 2025, 19:37 Daniel P. Berrangé wrote: > > > On Tue, May 06, 2025 at 07:17:25PM +0300, Elisha Hollander wrote: > > > Sorry for former patch something is messed up with my email. > > > > The commit message needs to explain what problem is being solved by > > making this change as allowing 0 bytes looks dubious on the surface. > > > > > > > > Signed-off-by: donno2048 > > > --- > > > util/memfd.c | 10 ++++++---- > > > 1 file changed, 6 insertions(+), 4 deletions(-) > > > > > > diff --git a/util/memfd.c b/util/memfd.c > > > index 8a2e906..e96e5af 100644 > > > --- a/util/memfd.c > > > +++ b/util/memfd.c > > > @@ -108,7 +108,7 @@ err: > > > void *qemu_memfd_alloc(const char *name, size_t size, unsigned int > > seals, > > > int *fd, Error **errp) > > > { > > > - void *ptr; > > > + void *ptr = NULL; > > > int mfd = qemu_memfd_create(name, size, false, 0, seals, NULL); > > > > > > /* some systems have memfd without sealing */ > > > @@ -131,9 +131,11 @@ void *qemu_memfd_alloc(const char *name, size_t > > size, > > > unsigned int seals, > > > } > > > } > > > > > > - ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0); > > > - if (ptr == MAP_FAILED) { > > > - goto err; > > > + if (size != 0) { > > > + ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0); > > > + if (ptr == MAP_FAILED) { > > > + goto err; > > > + } > > > } > > > > This patch is mangled. > > > > > > With regards, > > Daniel > > -- > > |: https://berrange.com -o- > > https://www.flickr.com/photos/dberrange :| > > |: https://libvirt.org -o- > > https://fstop138.berrange.com :| > > |: https://entangle-photo.org -o- > > https://www.instagram.com/dberrange :| > > > > With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|