From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39662) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fEAwM-0005Ah-IS for qemu-devel@nongnu.org; Thu, 03 May 2018 05:54:20 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fEAwH-0001ms-K6 for qemu-devel@nongnu.org; Thu, 03 May 2018 05:54:18 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:44358 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fEAwH-0001mm-EC for qemu-devel@nongnu.org; Thu, 03 May 2018 05:54:13 -0400 Date: Thu, 3 May 2018 17:53:59 +0800 From: Peter Xu Message-ID: <20180503095359.GE29580@xz-mi> References: <20180427095527.GE13269@xz-mi> <20180427114029.GF13269@xz-mi> <20180503060442.GB2378@xz-mi> <547a97a1-0ac0-21b2-af00-036b795b06cc@redhat.com> <20180503072828.GA29580@xz-mi> <8cbed1d0-1f4e-db6d-bd83-1042f724827a@redhat.com> <20180503075302.GC29580@xz-mi> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 08/10] intel-iommu: maintain per-device iova ranges List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jason Wang Cc: Jintack Lim , "Tian, Kevin" , "qemu-devel@nongnu.org" , Alex Williamson , "Michael S . Tsirkin" On Thu, May 03, 2018 at 05:22:03PM +0800, Jason Wang wrote: >=20 >=20 > On 2018=E5=B9=B405=E6=9C=8803=E6=97=A5 15:53, Peter Xu wrote: > > On Thu, May 03, 2018 at 03:43:35PM +0800, Jason Wang wrote: > > >=20 > > > On 2018=E5=B9=B405=E6=9C=8803=E6=97=A5 15:28, Peter Xu wrote: > > > > On Thu, May 03, 2018 at 03:20:11PM +0800, Jason Wang wrote: > > > > > On 2018=E5=B9=B405=E6=9C=8803=E6=97=A5 14:04, Peter Xu wrote: > > > > > > IMHO the guest can't really detect this, but it'll found that= the > > > > > > device is not working functionally if it's doing something li= ke what > > > > > > Jason has mentioned. > > > > > >=20 > > > > > > Actually now I have had an idea if we really want to live wel= l even > > > > > > with Jason's example: maybe we'll need to identify PSI/DSI. = For DSI, > > > > > > we don't remap for mapped pages; for PSI, we unmap and remap = the > > > > > > mapped pages. That'll complicate the stuff a bit, but it sho= uld > > > > > > satisfy all the people. > > > > > >=20 > > > > > > Thanks, > > > > > So it looks like there will be still unnecessary unamps. > > > > Could I ask what do you mean by "unecessary unmaps"? > > > It's for "for PSI, we unmap and remap the mapped pages". So for the= first > > > "unmap" how do you know it was really necessary without knowing the= state of > > > current shadow page table? > > I don't. Could I just unmap it anyway? Say, now the guest _modified= _ > > the PTE already. Yes I think it's following the spec, but it is > > really _unsafe_. We can know that from what it has done already. > > Then I really think a unmap+map would be good enough for us... After > > all that behavior can cause DMA error even on real hardwares. It can > > never tell. >=20 > I mean for following case: >=20 > 1) guest maps A1 (iova) to XXX > 2) guest maps A2 (A1 + 4K) (iova) to YYY > 3) guest maps A3 (A1 + 8K) (iova) to ZZZ > 4) guest unmaps A2 and A2, for reducing the number of PSIs, it can > invalidate A1 with a range of 2M >=20 > If this is allowed by spec, looks like A1 will be unmaped and mapped. My follow-up patch won't survive with this one but the original patch will work. Jason and I discussed a bit on IRC on this matter. Here's the conclusion we got: for now we use my original patch (which solves everything except PTE modifications). We mark that modify-PTE problem as TODO. Then at least we can have the nested device assignment work well on known OSs first. --=20 Peter Xu