[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] x86: mapping from Dom0 to DomU
Hi, Jan! On 04/21/2017 06:55 PM, Jan Beulich wrote: On 21.04.17 at 15:04, <andr2000@xxxxxxxxx> wrote:Hi, all! 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 So, the offending(?) code is at [1] which doesn't allow the mapping I want. When removed with diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index f35e3116bb25..aeb93be8b529 100644 --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -980,6 +980,7 @@ get_page_from_l1e( * dom0, until pvfb supports granted mappings. At that time this * minor hack can go away. */ +#if 0 if ( (real_pg_owner == NULL) || (pg_owner == l1e_owner) || xsm_priv_mapping(XSM_TARGET, pg_owner, real_pg_owner) ) { @@ -988,6 +989,7 @@ get_page_from_l1e( real_pg_owner?real_pg_owner->domain_id:-1); goto could_not_pin; } +#endif pg_owner = real_pg_owner; } I can successfully mmap and use pages from Dom0 in DomU. 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 grefs see 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 useoption 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]). Jan Thank you, Oleksandr[1] http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/include/public/grant_table.h;h=e5f04ec57c5bd590b6c81799ee01028c3512aacf;hb=refs/heads/master#l331 [2] http://lxr.free-electrons.com/source/mm/memory.c#L1569 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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