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spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:48012 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jJXIY-00026f-OO for qemu-devel@archiver.kernel.org; Wed, 01 Apr 2020 02:56:26 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60174) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jJXHZ-0001eN-Hp for qemu-devel@nongnu.org; Wed, 01 Apr 2020 02:55:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jJXHX-0005ba-Rk for qemu-devel@nongnu.org; Wed, 01 Apr 2020 02:55:25 -0400 Received: from mga12.intel.com ([192.55.52.136]:30620) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jJXHX-0005Ki-Ig for qemu-devel@nongnu.org; Wed, 01 Apr 2020 02:55:23 -0400 IronPort-SDR: egl5FReZawT5gDIYp0uc8d0Rba9djcKYGjSoJ4flQ8ZkW98gK1Jv7Wmeg+vdOxqaoUefnv2Rqa lfYWQp7PkXwQ== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 31 Mar 2020 23:55:19 -0700 IronPort-SDR: EWIASP2oX+cTy3Adk4ATPeyhpsSj4rD4qrkz9WvYD4ngZ48uD22bYrkKTyuoZdyKlQYRax1klH dGUlTLBHBaZQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,330,1580803200"; d="scan'208";a="422593997" Received: from joy-optiplex-7040.sh.intel.com (HELO joy-OptiPlex-7040) ([10.239.13.16]) by orsmga005.jf.intel.com with ESMTP; 31 Mar 2020 23:55:18 -0700 Date: Wed, 1 Apr 2020 02:45:44 -0400 From: Yan Zhao To: Alex Williamson Subject: Re: [PATCH] hw/vfio: let readonly flag take effect for mmaped regions Message-ID: <20200401064544.GG6631@joy-OptiPlex-7040> References: <20200327111934.71066-1-yan.y.zhao@intel.com> <20200327112537.2efd65ac@w520.home> <20200330013527.GA30683@joy-OptiPlex-7040> <20200330063402.GE30683@joy-OptiPlex-7040> <20200330085923.19d7345f@w520.home> <20200331015941.GD6631@joy-OptiPlex-7040> <20200331132827.514b73b0@w520.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200331132827.514b73b0@w520.home> User-Agent: Mutt/1.9.4 (2018-02-28) X-detected-operating-system: by eggs.gnu.org: FreeBSD 9.x [fuzzy] X-Received-From: 192.55.52.136 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Yan Zhao Cc: "pbonzini@redhat.com" , "Zeng, Xin" , "qemu-devel@nongnu.org" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Apr 01, 2020 at 03:28:27AM +0800, Alex Williamson wrote: > On Mon, 30 Mar 2020 21:59:41 -0400 > Yan Zhao wrote: > > > On Mon, Mar 30, 2020 at 10:59:23PM +0800, Alex Williamson wrote: > > > On Mon, 30 Mar 2020 02:34:02 -0400 > > > Yan Zhao wrote: > > > > > > > On Mon, Mar 30, 2020 at 09:35:27AM +0800, Yan Zhao wrote: > > > > > On Sat, Mar 28, 2020 at 01:25:37AM +0800, Alex Williamson wrote: > > > > > > On Fri, 27 Mar 2020 11:19:34 +0000 > > > > > > yan.y.zhao@intel.com wrote: > > > > > > > > > > > > > From: Yan Zhao > > > > > > > > > > > > > > currently, vfio regions without VFIO_REGION_INFO_FLAG_WRITE are only > > > > > > > read-only when VFIO_REGION_INFO_FLAG_MMAP is not set. > > > > > > > > > > > > > > regions with flag VFIO_REGION_INFO_FLAG_READ | VFIO_REGION_INFO_FLAG_MMAP > > > > > > > are only read-only in host page table for qemu. > > > > > > > > > > > > > > This patch sets corresponding ept page entries read-only for regions > > > > > > > with flag VFIO_REGION_INFO_FLAG_READ | VFIO_REGION_INFO_FLAG_MMAP. > > > > > > > > > > > > > > accordingly, it ignores guest write when guest writes to the read-only > > > > > > > regions are trapped. > > > > > > > > > > > > > > Signed-off-by: Yan Zhao > > > > > > > Signed-off-by: Xin Zeng > > > > > > > --- > > > > > > > > > > > > Currently we set the r/w protection on the mmap, do I understand > > > > > > correctly that the change in the vfio code below results in KVM exiting > > > > > > to QEMU to handle a write to a read-only region and therefore we need > > > > > > the memory.c change to drop the write? This prevents a SIGBUS or > > > > > > similar? > > > > > yes, correct. the change in memory.c is to prevent a SIGSEGV in host as > > > > > it's mmaped to read-only. we think it's better to just drop the writes > > > > > from guest rather than corrupt the qemu. > > > > > > > > > > > > > > > > > Meanwhile vfio_region_setup() uses the same vfio_region_ops for all > > > > > > regions and vfio_region_write() would still allow writes, so if the > > > > > > device were using x-no-mmap=on, I think we'd still get a write to this > > > > > > region and expect the vfio device to drop it. Should we prevent that > > > > > > write in QEMU as well? > > > > > yes, it expects vfio device to drop it right now. > > > > > As the driver sets the flag without VFIO_REGION_INFO_FLAG_WRITE, it should > > > > > handle it properly. > > > > > both dropping in qemu and dropping in vfio device are fine to us. > > > > > we wonder which one is your preference :) > > > > > > The kernel and device should always do the right thing, we cannot rely > > > on the user to honor the mapping, but it's also a reasonable response > > > from the kernel to kill the process with a SIGSEGV if the user ignores > > > the protections. So I don't think it's an either/or, the kernel needs > > > to do the right thing for itself and in this case QEMU should do the > > > right thing for itself, which is to drop writes for regions that don't > > > support it. So in general, I agree with your patch. > > > > > hi Alex > > so is there anything I need to do? do I need to add a write dropping in > > vfio_region_write() too? if yes, do I need to keep the > > trace_vfio_region_write() before dropping ? > > Hi Yan, > > Yes to both feels the most consistent, right? If we want the same > behavior between mmap'd and non-mmap'd regions, QEMU should drop both > writes. Your change to memory_region_ram_device_write() drops the > write after tracing. For both cases though it might be worthwhile to > have a separate trace recorded to indicate a dropped write, probably in > place of the normal trace to avoid confusion. Thanks, > got it. will do it. Thanks Yan