> -----Original Message----- > From: Jan Beulich [mailto:jbeul...@suse.com] > Sent: 22 January 2019 10:47 > To: Paul Durrant <paul.durr...@citrix.com> > Cc: Julien Grall <julien.gr...@arm.com>; Andrew Cooper > <andrew.coop...@citrix.com>; George Dunlap <george.dun...@citrix.com>; Ian > Jackson <ian.jack...@citrix.com>; Roger Pau Monne <roger....@citrix.com>; > Wei Liu <wei.l...@citrix.com>; Sander Eikelenboom <li...@eikelenboom.it>; > Chao Gao <chao....@intel.com>; Jun Nakajima <jun.nakaj...@intel.com>; > Kevin Tian <kevin.t...@intel.com>; Stefano Stabellini > <sstabell...@kernel.org>; xen-devel <xen-devel@lists.xenproject.org>; > Konrad Rzeszutek Wilk <konrad.w...@oracle.com>; Tim (Xen.org) > <t...@xen.org> > Subject: RE: [PATCH] iommu: specify page_count rather than page_order to > iommu_map/unmap()... > > >>> On 21.01.19 at 14:22, <paul.durr...@citrix.com> wrote: > >> -----Original Message----- > >> From: Jan Beulich [mailto:jbeul...@suse.com] > >> Sent: 21 January 2019 12:05 > >> To: Paul Durrant <paul.durr...@citrix.com> > >> Cc: Julien Grall <julien.gr...@arm.com>; Andrew Cooper > >> <andrew.coop...@citrix.com>; George Dunlap <george.dun...@citrix.com>; > Ian > >> Jackson <ian.jack...@citrix.com>; Roger Pau Monne > <roger....@citrix.com>; > >> Wei Liu <wei.l...@citrix.com>; Sander Eikelenboom > <li...@eikelenboom.it>; > >> Chao Gao <chao....@intel.com>; Jun Nakajima <jun.nakaj...@intel.com>; > >> Kevin Tian <kevin.t...@intel.com>; Stefano Stabellini > >> <sstabell...@kernel.org>; xen-devel <xen-devel@lists.xenproject.org>; > >> Konrad Rzeszutek Wilk <konrad.w...@oracle.com>; Tim (Xen.org) > >> <t...@xen.org> > >> Subject: RE: [PATCH] iommu: specify page_count rather than page_order > to > >> iommu_map/unmap()... > >> > >> >>> On 21.01.19 at 12:56, <paul.durr...@citrix.com> wrote: > >> >> -----Original Message----- > >> >> From: Jan Beulich [mailto:jbeul...@suse.com] > >> >> Sent: 21 January 2019 11:28 > >> >> To: Paul Durrant <paul.durr...@citrix.com> > >> >> Cc: Julien Grall <julien.gr...@arm.com>; Andrew Cooper > >> >> <andrew.coop...@citrix.com>; Roger Pau Monne <roger....@citrix.com>; > >> Wei > >> >> Liu <wei.l...@citrix.com>; Sander Eikelenboom > <li...@eikelenboom.it>; > >> >> George Dunlap <george.dun...@citrix.com>; Ian Jackson > >> >> <ian.jack...@citrix.com>; Chao Gao <chao....@intel.com>; Jun > Nakajima > >> >> <jun.nakaj...@intel.com>; Kevin Tian <kevin.t...@intel.com>; Stefano > >> >> Stabellini <sstabell...@kernel.org>; xen-devel <xen- > >> >> de...@lists.xenproject.org>; Konrad Rzeszutek Wilk > >> >> <konrad.w...@oracle.com>; Tim (Xen.org) <t...@xen.org> > >> >> Subject: Re: [PATCH] iommu: specify page_count rather than > page_order > >> to > >> >> iommu_map/unmap()... > >> >> > >> >> >>> On 18.01.19 at 17:03, <paul.durr...@citrix.com> wrote: > >> >> > ...and remove alignment assertions. > >> >> > > >> >> > Testing shows that certain callers of iommu_legacy_map/unmap() > >> specify > >> >> > order > 0 ranges that are not order aligned thus causing one of > the > >> >> > IS_ALIGNED() assertions to fire. > >> >> > >> >> As said before - without a much better explanation of why the > current > >> >> order-based model is unsuitable (so far I've been provided only > vague > >> >> pointers into "somewhere in PVH Dom0 boot code" iirc) to understand > >> >> why it's undesirable to simply make those call sites obey to the > >> current > >> >> requirements, I'm not happy to see us go this route. > >> > > >> > I thought... > >> > > >> > "Using a count actually makes more sense because the valid > >> > set of mapping orders is specific to the IOMMU implementation and to > it > >> > should be up to the implementation specific code to translate a > mapping > >> > count into an optimal set of mapping orders (when the code is finally > >> > modified to support orders > 0)." > >> > > >> > ...was reasonably clear. Is that not a reasonable justification? What > >> else > >> > could I say? > >> > >> Well, I was hoping to be pointed at the (apparently multiple) call > sites > >> where making them match the current function pattern is more involved > >> and/or less desirable than changing the functions here. > > > > AFAICT, one of them is memory.c:populate_physmap() where the extent > order > > comes from the memop_args and the memory comes from > alloc_domheap_pages(), > > which I don't believe aligns memory on the specified order. > > Of course it does (in MFN space). What I notice is that the gpfn passed > in is not validated to be suitably aligned for the specified order. With > guest_physmap_add_entry() processing each 4k page separately this > doesn't currently have any bad effects, but I think it's a bug > nevertheless. After all the comment in struct xen_memory_reservation's > declaration says "size/alignment of each". The issue with fixing flaws > like this is that there's always the risk of causing regressions with > existing guests. > > > Regardless of the > > alignment though, the fact that order comes from a hypercall argument > and may > > not match any of the orders supported by the IOMMU implementation makes > me > > think that using a page count is better. > > Splitting up guest requests is orthogonal to whether a count or an > order is more suitable as a parameter.
Ok, I'm not prepared to argue the point any more. I withdraw the patch. Paul > > Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
