Re: [Xen-devel] [PATCH v2 0/*] xen: xen-domid-restrict improvements

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of
> Ross Lagerwall
> Sent: 06 October 2017 13:58
> To: Ian Jackson <Ian.Jackson@xxxxxxxxxx>; qemu-devel@xxxxxxxxxx
> Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>; xen-
> devel@xxxxxxxxxxxxxxxxxxxx; Stefano Stabellini <sstabellini@xxxxxxxxxx>;
> Juergen Gross <jgross@xxxxxxxx>
> Subject: Re: [Xen-devel] [PATCH v2 0/*] xen: xen-domid-restrict
> improvements
> 
> On 10/04/2017 05:18 PM, Ian Jackson wrote:
> > (Resending this because 1. I got the CC for xen-devel wrong; 2. I got
> > the subject wrong: there are actually 8 patches; 3. I mangled
> > Anthony's name in theheaders.  Sorry for the noise.)
> >
> > I have been working on trying to get qemu, when running as a Xen
> > device model, to _actually_ not have power equivalent to root.
> >
> > I think I have achieved this, with some limitations (which will be
> > discussed in my series against xen.git.
> >
> > However, there are changes to qemu needed.  In particular
> >
> >   * The -xen-domid-restrict option does not work properly right now.
> >     It only restricts a small subset of the descriptors qemu has open.
> >     I am introducing a new library call in the Xen libraries for this,
> >     xentoolcore_restrict_all.
> >
> 
> Hi Ian,
> 
> I'm testing your QEMU and Xen patch series and found that after being
> restricted, QEMU fails to setup up the VGA memory properly which causes
> a complete stall with stdvga. With cirrus it mostly works although it
> seems to have reduced performance.
> 
> I think it happens when the VM sets up the BAR some time after
> xen_restrict() has been called. The failure comes from QEMU calling
> xc_domain_add_to_physmap() which calls do_memory_op() and finally
> xencall2(). But the underlying xencall fd has been replaced with /dev/null.

Oh, that's a PITA. This is because of the slightly hacky way that the VRAM is 
dealt with (it needing to be moved into the BAR of the PCI VGA device at the 
point where guest firmware programs it). Maybe we need a new dm_op for this?

  Paul

> 
> Here is some debug output, all of which occurs after the call to
> xentoolcore_restrict_all() has completed. 00:02.0 is the VGA device.
> 
> pci_update_mappings_add d=0x7fee0b154000 00:03.0
> 1,0xf0000000+0x1000000
> pci_update_mappings_add d=0x7fee0b1de000 00:02.0
> 0,0xf1000000+0x800000
> xen_client_set_memory 0xf1000000 size 0x800000, log_dirty 1
> xen: mapping vram to f1000000 - f1800000
> xen: add_to_physmap MFN 80000 to PFN f1000 failed: 25 (errno: 25)
> pci_update_mappings_add d=0x7fee0b154000 00:03.0 0,0xc000+0x100
> pci_update_mappings_add d=0x7fee0b1a4000 00:04.0 0,0xc100+0x100
> pci_update_mappings_add d=0x7fee0b1a4000 00:04.0 1,0xf1800000+0x100
> pci_update_mappings_add d=0x7fee0b006e00 00:01.2 4,0xc200+0x20
> pci_update_mappings_add d=0x7fee0b65c000 00:01.1 4,0xc220+0x10
> pci_update_mappings_add d=0x7fee0b65c000 00:01.1 4,0xc220+0x10
> pci_update_mappings_add d=0x7fee0b65c000 00:01.1 4,0xc220+0x10
> pci_update_mappings_add d=0x7fee0b65c000 00:01.1 4,0xc220+0x10
> pci_update_mappings_add d=0x7fee0b65c000 00:01.1 4,0xc220+0x10
> pci_update_mappings_add d=0x7fee0b65c000 00:01.1 4,0xc220+0x10
> pci_update_mappings_add d=0x7fee0b65c000 00:01.1 4,0xc220+0x10
> pci_update_mappings_add d=0x7fee0b65c000 00:01.1 4,0xc220+0x10
> pci_update_mappings_add d=0x7fee0b006e00 00:01.2 4,0xc200+0x20
> pci_update_mappings_add d=0x7fee0b006e00 00:01.2 4,0xc200+0x20
> pci_update_mappings_add d=0x7fee0b006e00 00:01.2 4,0xc200+0x20
> pci_update_mappings_add d=0x7fee0b006e00 00:01.2 4,0xc200+0x20
> pci_update_mappings_add d=0x7fee0b006e00 00:01.2 4,0xc200+0x20
> pci_update_mappings_add d=0x7fee0b006e00 00:01.2 4,0xc200+0x20
> pci_update_mappings_add d=0x7fee0b006e00 00:01.2 4,0xc200+0x20
> pci_update_mappings_add d=0x7fee0b1de000 00:02.0
> 0,0xf1000000+0x800000
> xen_client_set_memory 0xf1000000 size 0x800000, log_dirty 1
> pci_update_mappings_add d=0x7fee0b1de000 00:02.0
> 0,0xf1000000+0x800000
> xen_client_set_memory 0xf1000000 size 0x800000, log_dirty 1
> pci_update_mappings_add d=0x7fee0b1de000 00:02.0
> 0,0xf1000000+0x800000
> xen_client_set_memory 0xf1000000 size 0x800000, log_dirty 1
> pci_update_mappings_add d=0x7fee0b1de000 00:02.0
> 0,0xf1000000+0x800000
> xen_client_set_memory 0xf1000000 size 0x800000, log_dirty 1
> pci_update_mappings_add d=0x7fee0b1de000 00:02.0
> 0,0xf1000000+0x800000
> xen_client_set_memory 0xf1000000 size 0x800000, log_dirty 1
> pci_update_mappings_add d=0x7fee0b1de000 00:02.0
> 0,0xf1000000+0x800000
> xen_client_set_memory 0xf1000000 size 0x800000, log_dirty 1
> pci_update_mappings_add d=0x7fee0b1de000 00:02.0
> 0,0xf1000000+0x800000
> xen_client_set_memory 0xf1000000 size 0x800000, log_dirty 1
> pci_update_mappings_add d=0x7fee0b154000 00:03.0 0,0xc000+0x100
> pci_update_mappings_add d=0x7fee0b154000 00:03.0
> 1,0xf0000000+0x1000000
> pci_update_mappings_add d=0x7fee0b154000 00:03.0 0,0xc000+0x100
> pci_update_mappings_add d=0x7fee0b154000 00:03.0
> 1,0xf0000000+0x1000000
> pci_update_mappings_add d=0x7fee0b154000 00:03.0 0,0xc000+0x100
> pci_update_mappings_add d=0x7fee0b154000 00:03.0
> 1,0xf0000000+0x1000000
> pci_update_mappings_add d=0x7fee0b154000 00:03.0 0,0xc000+0x100
> pci_update_mappings_add d=0x7fee0b154000 00:03.0
> 1,0xf0000000+0x1000000
> pci_update_mappings_add d=0x7fee0b154000 00:03.0 0,0xc000+0x100
> pci_update_mappings_add d=0x7fee0b154000 00:03.0
> 1,0xf0000000+0x1000000
> pci_update_mappings_add d=0x7fee0b154000 00:03.0 0,0xc000+0x100
> pci_update_mappings_add d=0x7fee0b154000 00:03.0
> 1,0xf0000000+0x1000000
> pci_update_mappings_add d=0x7fee0b154000 00:03.0 0,0xc000+0x100
> pci_update_mappings_add d=0x7fee0b154000 00:03.0
> 1,0xf0000000+0x1000000
> 
> Apart from this issue, I was able to boot up and shut down a VM, using
> -xen-domid-restrict, -chroot, and -runasid.
> 
> There is a caveat when using -xen-domid-restrict and -chroot at the same
> time. The restriction happens after chrooting, so the chroot directory
> has to contain a valid /dev/null. This is a bit annoying and prevents
> the chroot being on a "nodev" mount.
> 
> Regards,
> --
> Ross Lagerwall
> 
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