From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46710) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z1zro-0005aS-Fk for qemu-devel@nongnu.org; Mon, 08 Jun 2015 12:25:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z1zrj-0008MH-OB for qemu-devel@nongnu.org; Mon, 08 Jun 2015 12:25:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33332) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z1zrj-0008LL-Id for qemu-devel@nongnu.org; Mon, 08 Jun 2015 12:25:35 -0400 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) by mx1.redhat.com (Postfix) with ESMTPS id 3E369B1F8C for ; Mon, 8 Jun 2015 16:25:35 +0000 (UTC) Date: Mon, 8 Jun 2015 18:25:32 +0200 From: "Michael S. Tsirkin" Message-ID: <20150608182206-mutt-send-email-mst@redhat.com> References: <1433776757-61958-1-git-send-email-imammedo@redhat.com> <1433776757-61958-4-git-send-email-imammedo@redhat.com> <5575B58B.50105@redhat.com> <20150608181314.3ab8fc80@nial.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150608181314.3ab8fc80@nial.brq.redhat.com> Subject: Re: [Qemu-devel] [RFC v2 3/6] memory: support unmapping of MemoryRegion mapped into HVA parent List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Igor Mammedov Cc: Paolo Bonzini , qemu-devel@nongnu.org On Mon, Jun 08, 2015 at 06:13:14PM +0200, Igor Mammedov wrote: > On Mon, 08 Jun 2015 17:32:27 +0200 > Paolo Bonzini wrote: > > > > > > > On 08/06/2015 17:19, Igor Mammedov wrote: > > > +void qemu_ram_unmap_hva(ram_addr_t addr) > > > +{ > > > + RAMBlock *block = find_ram_block(addr); > > > + > > > + assert(block); > > > + mmap(block->host, block->used_length, PROT_NONE, > > > + MAP_FIXED | MAP_NORESERVE | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); > > > +} > > > + > > > > Hmm, this is not good. :( The area at block->host can be in use, for > > example via memory_region_ref/memory_region_unref. This can happen a > > bit after the memory_region_del_subregion. So you can SEGV if you > > simply make a synchronous update. I'm not sure if there is a solution > Yep, that's the problem I haven't found solution to so far, > any ideas hoe to approach this are appreciated. > > issue is that we have to re-reserve HVA region first so no other allocation > would claim gap and the only way I found was just to call mmap() on it > which as side effect invalidates MemoryRegion's backing RAM. Well the only point we need to mmap is where we'd unmap normally, if that's not safe then unmapping wouldn't be safe either? > > (but thanks for splitting the patches in a way that made the problem > > clear!). > > > > Paolo