From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Chen, Tiejun" Subject: Re: [v3][PATCH 1/1] xen:vtd: missing RMRR mapping while share EPT Date: Fri, 25 Jul 2014 16:26:58 +0800 Message-ID: <53D214D2.7000703@intel.com> References: <1406199618-21574-1-git-send-email-tiejun.chen@intel.com> <53D22E550200007800025DD8@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: "Zhang, Yang Z" , Jan Beulich , "Tian, Kevin" Cc: "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org On 2014/7/25 16:24, Zhang, Yang Z wrote: > Jan Beulich wrote on 2014-07-25: >>>>> On 24.07.14 at 19:12, wrote: >>>>> From: Chen, Tiejun >>>> Sent: Thursday, July 24, 2014 4:00 AM >>>> >>>> intel_iommu_map_page() does nothing if VT-d shares EPT page table. >>>> So rmrr_identity_mapping() never create RMRR mapping but in some >>>> cases like some GFX drivers it still need to access RMRR. >>> >>> this is not accurate. as long as RMRR is reported, it's always >>> necessary to have the identity mapping there, not just needed in >>> SOME CASES. :-) >> >> Actually (as also said before) I think "in some cases" is quite correct: >> There's no guarantee that a device will actually access the region(s) >> an RMRR may specify for it. A particular example would be the USB case >> where iiuc these regions are needed only until legacy mode emulation gets turned off. > > Yes, even for Intel GFX, the RMRR is never really accessed. So we never saw any issue even without this patch. > Yang, Windows GFX driver really accesses this range now. Without this patch, the blue screen appears. Tiejun