Re: [Minios-devel] Can't map grant_table between domains

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Aug 02, 2016 at 12:10:11AM +0100, gotoc io wrote:
> Thanks Wei for an answer.
> 
> >>    >> OOI why do you setup grant table again?
> My intention is:
> 1. setup Grant Tables
> Creates a gnttab setup table t, which requests a grant table with a single
> element, stored in the grant table variable.
> >         setup_op.dom = DOMID_SELF;
> >         setup_op.nr_frames = 1;
> >         setup_op.frame_list = (uint64_t*)grant_table;
> >         HYPERVISOR_grant_table_op(GNTTABOP_setup_table, &setup_op, 1);
> 2. Offer grant to domain B
> frame is staticaly allocated 4k mem page, shift by 12 because as I
> understood we need to pass mem frame number
> >         grant_table[0].domid = B;
> >         grant_table[0].frame = *shared_page >> 12;

I notice this could be wrong -- not sure what shared_page is.

The frame should be machine frame. You might need to use virt_to_mfn to
get the mfn number.

> >         flags = GTF_permit_access & GTF_reading & GTF_writing;
> >         grant_table[0].flags = flags;
> 
> I also added wmb(); before setting flags as you suggested, but it doesn't
> help me.
> 
> > In any case, there is already a set of API that you can use from
> > gnttab.c and gntmap.c. Why not just use those?
> 
> The reason why I don't use API now was because of education purposes, but
> because now is not working I will try to offer grant using API and
> consume/map it using my function.
> As I understood I have to use these followed 3 function (init, alloc,
> access) to be able to offer grant (from: gnttab.h):
> 
> void init_gnttab(void);
> grant_ref_t gnttab_alloc_and_grant(void **map);
> grant_ref_t gnttab_grant_access(domid_t domid, unsigned long frame,
>                                 int readonly)
> 

Yeah. I would suggest using mini-os original implementation on both
sides to make sure everything works. Then I would replace one side
(granter / grantee) to your own implementation to figure out what goes
wrong.

You might also want to check as reference mini-os.git:netfront.c -- a
driver that uses grant table -- on how grant table is used.

> I also noticed that I got same error in dmesg if I run only mapper kernel:
> (XEN) grant_table.c:830:d42v0 Bad domain (0 != 42), or risk of counter
> overflow 00000002, or subpage 0

You might have to dig into hypervisor code to know what went wrong here.

> my next question "is there any possibility to ensure that offerer domain
> succesfully offer grant?" I am checking setup_op.status but it is always 0,
> and also it is set after hypercall, not after writing to grant_table itself.
> 

To offer a grant you just need to write to your already set up grant
table (plus appropriate barriers). No hypercall is needed.

The setup hypercall IIRC only tells the hypervisor that the grant table
of this guest consists of the following frames (as you see in the
hypercall arguments).

Wei.


> 
> Many Thanks
> 
> 
> On Mon, Aug 1, 2016 at 3:52 PM, Wei Liu <wei.liu2@xxxxxxxxxx> wrote:
> 
> > On Mon, Aug 01, 2016 at 03:11:48PM +0100, gotoc io wrote:
> > > Hi I was trying to make communication between Two mini-os domains.
> > > I have offerer and mapper domains, offerer has ID=A, mapper has ID=B.
> > >
> > >
> > > Offerer function:
> > >
> > >         setup_op.dom = DOMID_SELF;
> > >         setup_op.nr_frames = 1;
> > >         setup_op.frame_list = (uint64_t*)grant_table;
> > >         HYPERVISOR_grant_table_op(GNTTABOP_setup_table, &setup_op, 1);
> >
> > OOI why do you setup grant table again?
> >
> > >         grant_table[0].domid = B;
> > >         grant_table[0].frame = *shared_page >> 12;
> > >         flags = GTF_permit_access & GTF_reading & GTF_writing;
> > >         grant_table[0].flags = flags;
> > >
> >
> > Maybe missing some memory barriers?
> >
> > See gnttab.c:gnttab_grant_access.
> >
> > >
> > > Mapping function:
> > >
> > >         gnttab_map_grant_ref_t map_op;
> > >         map_op.host_addr = (uint64_t)shared_page;
> > >         map_op.flags = GNTMAP_host_map;
> > >         map_op.ref = entry;
> > >         map_op.dom = A;
> > >         HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &map_op,1);
> >
> > This looks reasonable to me.
> >
> > >
> > > After that I always got map_op.status == -1
> > > More over when I run xl dmesg I got followed error:
> > >
> > > (XEN) grant_table.c:830:d28v0 Bad domain (0 != B), or risk of counter
> > > overflow 00000002, or subpage 0
> > >
> > >
> > > Any idea what I can do in wrong way? I was trying to follow way how vTPM
> > > driver is working but after faced this error I can't move forward.
> > >
> >
> > In any case, there is already a set of API that you can use from
> > gnttab.c and gntmap.c. Why not just use those?
> >
> > Wei.
> >
> > > Thanks for any help.
> >
> > > _______________________________________________
> > > Minios-devel mailing list
> > > Minios-devel@xxxxxxxxxxxxxxxxxxxx
> > > https://lists.xenproject.org/cgi-bin/mailman/listinfo/minios-devel
> >
> >

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