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

Thomas Huth
2023-11-22T11:06:48Z

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?

Thanks,
Thomas