[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] x86: mapping from Dom0 to DomU
On 04/24/2017 09:43 AM, Jan Beulich wrote: On 24.04.17 at 08:10, <andr2000@xxxxxxxxx> wrote:On 04/21/2017 06:55 PM, Jan Beulich wrote:On 21.04.17 at 15:04, <andr2000@xxxxxxxxx> wrote:I am working on a zero-copy scenario for x86 and for that I am mapping pages from Dom0 to DomU (yes, I know there are at least security concerns). Everything is just fine, e.g. I can map grefs from Dom0 in DomU with gnttab_map_refs, until I try to mmap those pages in DomU with vm_insert_page and Xen starts to complain: (XEN) mm.c:989:d1v0 pg_owner 1 l1e_owner 1, but real_pg_owner 0 (XEN) mm.c:1061:d1v0 Error getting mfn 20675a (pfn 1ac8de) from L1 entry 800000020675a027 for l1e_owner=1, pg_owner=1 Can anybody please explain why the use-case I am trying to implement is treated as error from Xen's POV and what would be the right way to do so?Granted pages can be mapped only through the grant-table hypercall,If this is gnttab_map_refs call you mean then, yes, I do that to map grefssee public/grant_table.h's explanation of GNTMAP_host_map used with out without GNTMAP_contains_pte.I know about these options and according to [1] I can use option to map with "host virtual address", e.g. without GNTMAP_contains_pte flag, because GNTMAP_contains_pte requires me to provide machine address which I don't want.Other mapping attempts have to be refused, or else the accounting done by the grant table code would be undermined.So, either I didn't understand what you mean or was not clear to explain that I see no problem while mapping grefs with gnttab_map_refs, but see the problem when vm_insert_page is called to mmap the pages into user-space (vm_insert_page internally does set_pte_at which it silently fails, but kernel knows nothing about that because no error reported [2]).Indeed you seem to have misunderstood: _All_ mappings of the granted page need to be done using the grant table hypercalls, not just the initial one. set_pte() establishes a second mapping, and that does not use the grant table op. Jan thank you, it seems like I'll have to duplicate code from gntdev [1], so my use-case also works on x86, not only ARM [1] http://lxr.free-electrons.com/source/drivers/xen/gntdev.c#L981 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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