RE: staging: unable to restore HVM with Viridian param set

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
> Sent: 02 February 2021 00:20
> To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>; Tamas K Lengyel 
> <tamas.k.lengyel@xxxxxxxxx>; Xen-devel
> <xen-devel@xxxxxxxxxxxxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Ian Jackson 
> <iwj@xxxxxxxxxxxxxx>; Anthony
> PERARD <anthony.perard@xxxxxxxxxx>; Paul Durrant <paul@xxxxxxx>
> Subject: Re: staging: unable to restore HVM with Viridian param set
> 
> n 01/02/2021 22:57, Andrew Cooper wrote:
> > On 01/02/2021 22:51, Tamas K Lengyel wrote:
> >> Hi all,
> >> trying to restore a Windows VM saved on Xen 4.14 with Xen staging results 
> >> in:
> >>
> >> # xl restore -p /shared/cfg/windows10.save
> >> Loading new save file /shared/cfg/windows10.save (new xl fmt info 
> >> 0x3/0x0/1475)
> >>  Savefile contains xl domain config in JSON format
> >> Parsing config from <saved>
> >> xc: info: Found x86 HVM domain from Xen 4.14
> >> xc: info: Restoring domain
> >> xc: error: set HVM param 9 = 0x0000000000000065 (17 = File exists):
> >> Internal error
> >> xc: error: Restore failed (17 = File exists): Internal error
> >> libxl: error: libxl_stream_read.c:850:libxl__xc_domain_restore_done:
> >> restoring domain: File exists
> >> libxl: error: libxl_create.c:1581:domcreate_rebuild_done: Domain
> >> 8:cannot (re-)build domain: -3
> >> libxl: error: libxl_domain.c:1182:libxl__destroy_domid: Domain
> >> 8:Non-existant domain
> >> libxl: error: libxl_domain.c:1136:domain_destroy_callback: Domain
> >> 8:Unable to destroy guest
> >> libxl: error: libxl_domain.c:1063:domain_destroy_cb: Domain
> >> 8:Destruction of domain failed
> >>
> >> Running on staging 419cd07895891c6642f29085aee07be72413f08c
> >
> > CC'ing maintainers and those who've edited the code recently.
> >
> > What is happening is xl/libxl is selecting some viridian settings,
> > applying them to the domain, and then the migrations stream has a
> > different set of viridian settings.
> >
> > For a migrating-in VM, nothing should be set during domain build.
> > Viridian state has been part of the migrate stream since before mig-v2,
> > so can be considered to be everywhere relevant now.
> 
> The fallout is likely from my changes that modified default set of viridian
> settings. The relevant commits:
> 983524671031fcfdb24a6c0da988203ebb47aebe
> 7e5cffcd1e9300cab46a1816b5eb676caaeed2c1
> 
> The same config from migrated domains now implies different set of viridian
> extensions then those set at the source side. That creates inconsistency in
> libxl. I don't really know how to address it properly in libxl other than
> don't extend the default set ever.
> 

Surely it should be addressed properly in libxl by not messing with the 
viridian settings on migrate-in/resume, as Andrew says? TBH I thought this was 
already the case. There should be no problem with adding to the default set as 
this is just an xl/libxl concept; the param flags in Xen are always define the 
*exact* set of enabled enlightenments.

  Paul


> Igor