From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43264) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZEruA-0006OU-Kp for qemu-devel@nongnu.org; Tue, 14 Jul 2015 00:33:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZErtz-0003CX-Qw for qemu-devel@nongnu.org; Tue, 14 Jul 2015 00:33:18 -0400 Date: Tue, 14 Jul 2015 13:46:44 +1000 From: David Gibson Message-ID: <20150714034644.GC4121@voom.redhat.com> References: <1436525028-23963-1-git-send-email-aik@ozlabs.ru> <1436525028-23963-2-git-send-email-aik@ozlabs.ru> <20150713061539.GB4121@voom.redhat.com> <55A367A1.50707@ozlabs.ru> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="vOmOzSkFvhd7u8Ms" Content-Disposition: inline In-Reply-To: <55A367A1.50707@ozlabs.ru> Subject: Re: [Qemu-devel] [PATCH qemu 1/5] vfio: Switch from TARGET_PAGE_MASK to qemu_real_host_page_mask List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexey Kardashevskiy Cc: Alex Williamson , qemu-ppc@nongnu.org, qemu-devel@nongnu.org --vOmOzSkFvhd7u8Ms Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Jul 13, 2015 at 05:24:17PM +1000, Alexey Kardashevskiy wrote: > On 07/13/2015 04:15 PM, David Gibson wrote: > >On Fri, Jul 10, 2015 at 08:43:44PM +1000, Alexey Kardashevskiy wrote: > >>These started switching from TARGET_PAGE_MASK (hardcoded as 4K) to > >>a real host page size: > >>4e51361d7 "cpu-all: complete "real" host page size API" and > >>f7ceed190 "vfio: cpu: Use "real" page size API" > >> > >>This finished the transition by: > >>- %s/TARGET_PAGE_MASK/qemu_real_host_page_mask/ > >>- %s/TARGET_PAGE_ALIGN/REAL_HOST_PAGE_ALIGN/ > >>- removing bitfield length for offsets in VFIOQuirk::data as > >>qemu_real_host_page_mask is not a macro > > > >This does not make much sense to me. f7ceed190 moved to > >REAL_HOST_PAGE_SIZE because it's back end stuff that really depends > >only on the host page size. > > > >Here you're applying a blanket change to vfio code, in particular to > >the DMA handling code, and for DMA both the host and target page size > >can be relevant, depending on the details of the IOMMU implementation. >=20 >=20 > 5/5 uses this listener for memory preregistration - this totally depends = on > the host page size. It was suggested to make this listener do memory > preregistration too, not just DMA. >=20 >=20 > >>This keeps using TARGET_PAGE_MASK for IOMMU regions though as it is > >>the minimum page size which IOMMU regions may be using and at the moment > >>memory regions do not carry the actual page size. > > > >And this exception also doesn't make much sense to me. Partly it's > >confusing because the listener is doing different things depending on > >whether we have a guest visible IOMMU or not. >=20 > Yes... >=20 > >In short, there doesn't seem to be a coherent explanation here of > >where the page size / alignment restriction is coming from, and > >therefore whether it needs to be a host page alignment, a guest page > >alignment, or both. > > > >>Signed-off-by: Alexey Kardashevskiy > >>--- > >> > >>In reality DMA windows are always a lot bigger than a single 4K page > >>and aligned to 32/64MB, may be only use here > >>qemu_real_host_page_mask? > > > >I don't understand this question either. >=20 > The listener is called on RAM regions and DMA windows. If it is a RAM > region, then host page size applies. If it is a DMA window - then > 4K. That might be true in the particular cases you're thinking about, but you've got to think more generally if you're going to have coherent semantics in the core code here. For preregistration, host page size applies. For auto-mapping of RAM regions (as on x86), host IOMMU page size applies (which is probably the same as host page size, but it doesn't theoretically have to be). Guest page size kind of implicitly applies, since added RAM regions generally have to be target page aligned anyway. For guest controlled mapping, you're contrained by both the host iommu page size and the guest iommu page size. --=20 David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson --vOmOzSkFvhd7u8Ms Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJVpIYkAAoJEGw4ysog2bOSmtQQAJgvEqORSq2s3ZPEe03Lp5An t75stTEifgSqqQZSk7fB0QIJHzXzUzisifTA0pcWFUSWxdmVUYVUT2OWESNF1iaX Fa9c16YexNqDOe3x2A7KxA3kdFZaDmSEbMKYBLKeqQv0we6fLUAW5M3mUe/LlFv9 eSBXCEB/Zo3ywJHOrast1XgmDhPDzarjOp+YeXmZeFzy6D4AZxgpTv/Fs/xlZAPj J7oCoMld+t61QZ5p/toXDBMlovrlRUf1T9ay3V7mYJFv5H5C8Jh4pIAN5qq64Yk3 GkRntDK6alb9F8WQ8tmO+181URT1sV43uijAuobzJZnW7KWUx2TldKpnzdqxyRtF tQoIrckvuwJ6ELWgltBKO6xbnBCHG8VDruvEUgMKK1uELPC8S//hH+ZL3kOL83ok Iq68/gkZCU1Xancuo+jy77pZ5psOGaYU+9uIhMxhcBeZ2U01cHnrh6N+yTrkv7np Ht80+UTdQG8/uxUsP4aKfL565rM5rIGk3VP1LjpbmCuGBqWzVWp8b/OSGHdeRfdf eOXDvKkMfZwazY1iFxLOvaL1hIKNgcG1GzvmEyopRbZEZCu7XvqDX9LOypDUiGUn 0nJyssZ9tdT++gqKeMRqK5W/rM49/zmrqjtHtjozt/DMtrOG4ipV0fWwLbE8KwS0 Vu8wcraNNL/MOhMnXg6O =OclP -----END PGP SIGNATURE----- --vOmOzSkFvhd7u8Ms--