Re: [kvm-unit-tests GIT PULL 07/26] s390x: sie: ensure guests are aligned to 2GB

Nico Boehr
2023-11-23T14:16:56Z

Quoting Nina Schoetterl-Glausch (2023-11-23 10:24:12)
> On Wed, 2023-11-22 at 12:06 +0100, Thomas Huth wrote:
> > On 10/11/2023 14.52, Nico Boehr wrote:
> > > Until now, kvm-unit-tests has aligned guests to 1 MB in the host virtual
> > > address space. Unfortunately, some s390x environments require guests to
> > > be 2GB aligned in the host virtual address space, preventing
> > > kvm-unit-tests which act as a hypervisor from running there.
> > >
> > > We can't easily put guests at address 0, since we want to be able to run
> > > with MSO/MSL without having to maintain separate page tables for the
> > > guest physical memory. 2GB is also not a good choice, since the
> > > alloc_pages allocator will place its metadata there when the host has
> > > more than 2GB of memory. In addition, we also want a bit of space after
> > > the end of the host physical memory to be able to catch accesses beyond
> > > the end of physical memory.
> > >
> > > The vmalloc allocator unfortunately allocates memory starting at the
> > > highest virtual address which is not suitable for guest memory either
> > > due to additional constraints of some environments.
> > >
> > > The physical page allocator in memalign_pages() is also not a optimal
> > > choice, since every test running SIE would then require at least 4GB+1MB
> > > of physical memory.
> > >
> > > This results in a few quite complex allocation requirements, hence add a
> > > new function sie_guest_alloc() which allocates memory for a guest and
> > > then establishes a properly aligned virtual space mapping.
> > >
> > > Rework snippet test and sie tests to use the new sie_guest_alloc()
> > > function.
> > >
> > > Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> > > Link: https://lore.kernel.org/r/20231106170849.1184162-3-nrb@linux.ibm.com
> > > Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
> > > ---
> > > lib/s390x/sie.h | 2 ++
> > > lib/s390x/snippet.h | 9 +++------
> > > lib/s390x/sie.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> > > s390x/sie.c | 4 ++--
> > > 4 files changed, 49 insertions(+), 8 deletions(-)
> >
> > Hi Nico!
> >
> > a colleague of mine (Jan) told me today that the current SIE-related tests
> > of the kvm-unit-tests are failing when being run from a KVM guest (i.e. when
> > we're testing a double-nested scenario). I've bisected the problem and ended
> > up with this patch here.
> > Could you please check whether "./run_tests.sh sie mvpg-sie spec_ex-sie"
> > still works for you from within a KVM guest?
>
> If you're getting a validity intercept, this should be fixed by
> KVM: s390: vsie: fix wrong VIR 37 when MSO is used
> https://lore.kernel.org/kvm/20231102153549.53984-1-imbrenda@linux.ibm.com/

After discussion with Thomas offline: yes it was a validity and yes the
patch mentioned by Nina fixes it.

Thanks.