From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: [PATCH v2] x86/p2m-pt: tighten conditions of IOMMU mapping updates Date: Thu, 1 Oct 2015 17:16:40 +0100 Message-ID: <560D5C68.10109@citrix.com> References: <560D261D02000078000A760A@prv-mh.provo.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 1ZhgXG-0007lW-AP for xen-devel@lists.xenproject.org; Thu, 01 Oct 2015 16:16:46 +0000 In-Reply-To: <560D261D02000078000A760A@prv-mh.provo.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 , xen-devel Cc: George Dunlap , Andrew Cooper , Wei Liu List-Id: xen-devel@lists.xenproject.org On 01/10/15 11:25, Jan Beulich wrote: > Whether the MFN changes does not depend on the new entry being valid > (but solely on the old one), and the need to update or TLB-flush also > depends on permission changes. > > Signed-off-by: Jan Beulich Reviewed-by: George Dunlap > --- > v2: Split from larger patch. Fix logic determining whether to update/ > flush IOMMU mappings. > --- > TBD: As already mentioned on the large-page-MMIO-mapping patch, there > is an apparent inconsistency with PoD handling: 2M mappings get > valid entries created, while 4k mappings don't. It would seem to > me that the 4k case needs changing, even if today this may only > be a latent bug. Question of course is why we don't rely on > p2m_type_to_flags() doing its job properly and instead special > case certain P2M types. The inconsistency in the conditionals there is a bit strange; but I'm pretty sure that in the 2MB case it is (at the moment) superfluous, because at the moment it seems that when setting a page with type p2m_populate_on_demand, it's always passing in _mfn(0), which is valid. (It used to pass a magic MFN, but Tim Deegan switched it to _mfn(0) at some point without comment.)