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Re: [Xen-devel] Re: Linux Stubdom Problem

To: Tim Deegan <tim@xxxxxxx>
Subject: Re: [Xen-devel] Re: Linux Stubdom Problem
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Tue, 23 Aug 2011 13:59:06 +0100
Cc: Anthony, "Xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, Jiageng Yu <yujiageng734@xxxxxxxxx>, PERARD <anthony.perard@xxxxxxxxx>, Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>
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References: <alpine.DEB.2.00.1107291601070.12963@kaball-desktop> <CAJ0pt15t_7==0rX9qEHyDMBRWUgfpMyLCmP0yBJsZg410FoutA@xxxxxxxxxxxxxx> <alpine.DEB.2.00.1107291617130.12963@kaball-desktop> <CAJ0pt15MVvw5_rJ_xFxR6aQpRYtTWFmR0OHJ54wuXSE+7hNkGQ@xxxxxxxxxxxxxx> <alpine.DEB.2.00.1107291628000.12963@kaball-desktop> <CAJ0pt155eqcyUwd-m--m3n+t-hLYixe+xA8J5MWgEWj58+o_Gw@xxxxxxxxxxxxxx> <CAJ0pt14OXshWn5NQ3JSfqRNdHkWMyhKWC0OwMixu9Xmk0b1oqw@xxxxxxxxxxxxxx> <alpine.DEB.2.00.1108190027450.12963@kaball-desktop> <CAJ0pt16CLqt+bHUwvO_V=c39CqN4Y4BCgbcSW26wik4hFTHq_g@xxxxxxxxxxxxxx> <alpine.DEB.2.00.1108221834340.12963@kaball-desktop> <20110823100719.GD96414@xxxxxxxxxxxxxxxxxxxxx>
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On Tue, 23 Aug 2011, Tim Deegan wrote:
> At 20:36 +0100 on 22 Aug (1314045383), Stefano Stabellini wrote:
> > The current implementation of IOCTL_PRIVCMD_MMAPBATCH is only capable of
> > mapping foreign mfns into the address space of the caller, while we need
> > to remap a set of pages already mapped in the address space of the
> > caller to some gmfns of a foreign domain. In other words we need the
> > same functionality but in the other direction.
> 
> I think I was confused whan you told me about this yesterday.  Do you
> need to map some of the linux-qemu-dom's memory into the guest?
> In that case, I think you can just grant the pages to the guest VM and
> use XENMAPSPACE_grant_table to map them. 

Yes, the pages I need to map into the guest have been vmalloc'ed by
xen_fbfront and mmap'ed into Qemu.
I didn't realize we could use any gmfn we wanted with
XENMAPSPACE_grant_table.

Jiageng: in the Linux implementation of the new ioctl, you can just call
gnttab_grant_foreign_access to grant access to the guest to framebuffer,
then you can use HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp) with
XENMAPSPACE_grant_table and the returned grant reference as idx to map
the pages into the guest.

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