From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH] libxl: fix "xl mem-set" regression from 0c029c4da2 Date: Wed, 22 Apr 2015 16:36:27 +0100 Message-ID: <1429716987.30934.44.camel@citrix.com> References: <5537A9E80200007800074B19@mail.emea.novell.com> <1429711278.30934.14.camel@citrix.com> <5537CF2A0200007800074C20@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1Ykwjs-0007aj-HR for xen-devel@lists.xenproject.org; Wed, 22 Apr 2015 15:39:00 +0000 In-Reply-To: <5537CF2A0200007800074C20@mail.emea.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: Ian Jackson , Wei Liu , xen-devel , Stefano Stabellini List-Id: xen-devel@lists.xenproject.org On Wed, 2015-04-22 at 15:41 +0100, Jan Beulich wrote: > >>> On 22.04.15 at 16:01, wrote: > > On Wed, 2015-04-22 at 13:02 +0100, Jan Beulich wrote: > >> Said commit ("libxl_set_memory_target: retain the same maxmem offset on > >> top of the current target") caused a regression for "xl mem-set" > >> against Dom0: While prior to creation of the first domain this works, > >> the first domain creation involving ballooning breaks. Due to "enforce" > >> not being set in the domain creation case, and due to Dom0's initial > >> ->max_pages (in the hypervisor) being UINT_MAX, the calculation of > >> "memorykb" in the first "xl mem-set" adusting the target upwards > >> subsequent to domain creation and termination may cause an overflow, > >> resulting in Dom0's maximum getting to a very small value. This small > >> maximum will the make the subsequent setting of the PoD target fail. > >> > >> Signed-off-by: Jan Beulich > >> --- > >> Note that this only fixes the immediate problem - there appear to be > >> further issues lurking here: > >> - libxl_set_memory_target()'s *_memkb variables all being 32-bit, > >> - libxl_domain_setmaxmem()'s max_memkb parameter being 32-bit, > > > > I think that increasing the width of these variables wouldn't break the > > API guarantee which we make, at least not in a practical way, since any > > existing 32-bit arguments passed will just get promoted. > > No, not even on 64-bit. On 32-bit, two arguments slots are needed > for what so far requires only one. On 64-bit (at least x86-64), the > calling code isn't required to zero-extend a value calculated in a > register (e.g. a result of earlier calculations which had more than > 32 significant bits could be passed unchanged to the called function); > it just so happens that 32-bit arithmetic on registers would always > implicitly zero the upper halves (and iirc that's the same on ARM64). You seem to be talking about ABI? As I tried to note in my response for libxl we only make guarantees about the API (P not B in the middle). Ian.