Re: [Xen-devel] PVH Dom0 with latest Linux kernels

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, Mar 13, 2014 at 07:09:54PM -0700, Mukesh Rathor wrote:
> On Fri, 28 Feb 2014 17:15:08 -0800
> Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
> 
> > On Tue, 18 Feb 2014 17:47:04 -0800
> > Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
> > 
> > > On Tue, 18 Feb 2014 17:48:02 +0100
> > > Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
> > > 
> > > > Hello,
> > > > 
> > > > I've tried to boot a PVH Dom0 using Linux 3.14.0-rc3 and Mukesh's
> > > > PVH Dom0 Xen tree
> > > > (https://oss.oracle.com/git/?p=mrathor/xen.git;a=shortlog;
> > > > h=dom0pvh-v7), and got the following crash. Do you have any new
> > > > Xen Dom0 series that I could use to test PVH Dom0?
> > > > 
> > > 
> > > It won't work. The final linux patches were changed a bit, and it
> > > makes an hcall that will cause mem corruption in xen. So, just hang
> > > in there a bit, new patches coming up in few days.
> > > 
> > > thanks
> > > Mukesh
> > 
> > Hey Roger,
> > 
> > Sorry, still don't have the new version out. Just running into one
> > issue after another... I had to refresh the tree, that broke my tools
> > as they needed newer glibc, which caused me to reinstall, which caused
> > dom0 to break causing me to rebuild that entire thing... anyways, I
> > ve got stuff up, but guests are not starting right now. Debugging.
> > Will keep you posted.
> 
> JFYI... I am able to boot dom0 in PVH mode, then start PV and PVH guest.
> But for HVM guest, during boot I see PF fautls in different places during 
> load of acpi-cpufreq module. Very hard to debug since faults come from
> different place everytime. I'm now trying to figure what load_module
> does thruout.
> 
> [    3.804141] BUG: unable to handle kernel paging request at 00000014bf0d13c8
> [    3.805127] IP: [<ffffffff8104c87c>] apply_relocate_add+0x7c/0x150
> [    3.805127] PGD 0
> 
> ------
> [    3.779263] BUG: unable to handle kernel NULL pointer dereference at       
>     (null)
> [    3.780250] IP: [<ffffffff810eadf3>] add_unformed_module+0x23/0x150
> [    3.780250] PGD 0
> [    3.780250] Oops: 0002 [#1] SMP
> --------
> [    3.975346] BUG: unable to handle kernel paging request at 0000000000003100
> [    3.976333] IP: [<ffffffff8130276d>] memcpy+0xd/0x110
> [    3.976333] PGD 0
> [    3.976333]  [<ffffffff810ede36>] ? layout_and_allocate+0x756/0xc00
> [    3.976333]  [<ffffffff810ee3f1>] load_module+0x111/0x18b0
> 
> 
> Strange, not sure why the problem is on PVH dom0 only... anyways,
> debugging. The problem is intermittent and sometimes it boots just
> fine...

The other thing that might be worth thinking - the virtual address that
modules are loaded on are way way at the end of the pagetables. Could
it be that the EPT is limited and said L4 entry (or L3) is shared with
Xen or hadn't been properly setup?

Oh wait, this is for HVM guests! And of course this problem you
see only occurs _after_ you have started PV and PVH guest right? If you
start the HVM guests first there are no problems?

Could you describe the steps and perhaps post a link to your updated git
tree for both Linux and Xen? More folks reproducing it could help with this.
(Like it helped with the other WP flag).
> 
> thanks
> Mukesh
> 
> 
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