From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36208) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fE93L-0000fg-72 for qemu-devel@nongnu.org; Thu, 03 May 2018 03:53:24 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fE93I-0005On-JD for qemu-devel@nongnu.org; Thu, 03 May 2018 03:53:23 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:60950 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 1fE93I-0005OM-D7 for qemu-devel@nongnu.org; Thu, 03 May 2018 03:53:20 -0400 Date: Thu, 3 May 2018 15:53:02 +0800 From: Peter Xu Message-ID: <20180503075302.GC29580@xz-mi> References: <20180427072810.GB13269@xz-mi> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <8cbed1d0-1f4e-db6d-bd83-1042f724827a@redhat.com> 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: "Tian, Kevin" , "Michael S . Tsirkin" , Alex Williamson , Jintack Lim , "qemu-devel@nongnu.org" On Thu, May 03, 2018 at 03:43:35PM +0800, Jason Wang wrote: >=20 >=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: > > >=20 > > > 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 like w= hat > > > > Jason has mentioned. > > > >=20 > > > > Actually now I have had an idea if we really want to live well ev= en > > > > 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 should > > > > 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"? >=20 > It's for "for PSI, we unmap and remap the mapped pages". So for the fir= st > "unmap" how do you know it was really necessary without knowing the sta= te 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 > > > How about record the mappings in the tree too? > > As I mentioned, for L1 guest (e.g., DPDK applications running in L1) > > it'll be fine. But I'm just afraid we will have other use cases, lik= e > > the L2 guests. That might need tons of the mapping entries in the > > worst case scenario. > >=20 >=20 > Yes, but that's the price of shadow page tables. So that's why I would like to propose this mergable interval tree. It might greatly reduce the price if we can reach a consensus on how we should treat those strange-behaved guest OSs. Thanks, --=20 Peter Xu