[Xen-devel] PV guest + shadow mode translate causing hang

["Aravindh Puthiyaparambil (aravindp)" <aravindp@xxxxxxxxx>]

I am trying to implement mem_access for PV guests using shadow pagetables. I am 
enabling shadow mode for pv using the following call:
xc_shadow_control(xch, domain_id,  XEN_DOMCTL_SHADOW_OP_ENABLE,  NULL, 0, NULL, 
0, NULL);

This seems to work and I can see a lot of shadow activity if I turn on 
debugtrace (xl debug T). However I see that the p2m table does not get 
initialized in this shadow mode. So I tried enabling refcount and translate 
modes:
xc_shadow_control(xch, domain_id,  XEN_DOMCTL_SHADOW_OP_ENABLE,  NULL, 0, NULL, 
XEN_DOMCTL_SHADOW_ENABLE_REFCOUNT | XEN_DOMCTL_SHADOW_ENABLE_TRANSLATE, NULL);

But this is causing the guest and host to hang. I turned on debugtrace and all 
I see on the serial console is the following:

1 sh: sh_set_allocation(): current 0 target 1024
2 p2m: p2m_alloc_table(): allocating p2m table
3 p2m: p2m_alloc_table(): populating p2m table
4 p2m: p2m_alloc_table(): p2m table initialised (65536 pages)
5 sh: sh_resync_all(): d=1, v=0
6 sh: sh_update_cr3__guest_4(): d=1 v=0 guest_table=54bc6
7 shdebug: sh_make_shadow(): (54bc6, 13)=>52651
8 sh: set_shadow_status(): d=1, v=0, gmfn=54bc6, type=0000000d, smfn=52651
9 sh: sh_set_toplevel_shadow(): 4/4 [0] gmfn 0x54bc6 smfn 0x52651
10 sh: sh_resync_all(): d=1, v=0
11 sh: sh_page_fault__guest_4(): d:v=1:0 va=0xffff88000fc0bd80 err=2, 
rip=ffff82d08018b26a
12 sh: sh_page_fault__guest_4(): not a shadow fault

At this point the guest and host are unresponsive. Any idea what is going on?

This is with an Ubuntu 12.04 PV guest (3.2.0-48-virtual kernel) with the 
following configuration:
builder = 'linux'
bootloader ="pygrub"
memory = 256
name = 'ubuntu-min-pv'
vcpus = 1
vif = [ 'type=vif, ip=192.168.0.1' ]
disk = ['/dev/sdc,raw,xvda,w']

Thanks,
Aravindh


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