Re: [RFC/PATCH v2 00/22] KVM/s390: Hugetlbfs enablement

[David Hildenbrand <david@redhat.com>]

On 20.12.2017 13:23, Christian Borntraeger wrote:
> FWIW, this patch set has survived some testing on my side (with storage
> keys, with VSIE, with both), so I would say that after a respin with some 
> patch sqashing we give it some more days for the last reviews and then apply
> the whole thing via a topic branch via Martins s390 tree. I will merge
> this branch as well to solve the potential conflicts with 
> Davids patch ( s390x/mm: cleanup gmap_pte_op_walk() ) which is still
> pending in my tree
> 

"postcopy works every second try, seems to be QEMU or my setup".
Shouldn't we first understand why? gmap is a very sensible topic and we
should rather spend more time understanding everything. We don't want
guest escalation bugs.

I'd love to spend more time reviewing this, but it won't happen within
the next 2 weeks (Christmas holidays)

Thanks!

> Christian
> 
> 
> 
> 
> 
> On 12/13/2017 01:53 PM, Janosch Frank wrote:
>> Since the z10 s390 does support 1M pages, but whereas hugetlbfs
>> support was added quite fast, KVM always used standard 4k pages for
>> guest backings.
>>
>> This patchset adds full support for 1M huge page backings for s390
>> KVM guests. I.e. we also support VSIE (nested vms) for these guests
>> and are therefore able to run all combinations of backings for all
>> layers of guests.
>>
>> When running a VSIE guest in a huge page backed guest, we need to
>> split some huge pages to be able to set granular protection. This way
>> we avoid a prot/unprot cycle if prefixes and VSIE pages containing
>> level 3 gmap DAT tables share the same segment, as the prefix has to
>> be accessible at all times and the VSIE page has to be write
>> protected.
>>
>> TODO:
>> * Cleanups & Documentation
>> * Refactoring to get rid of a lot of indents
>> * Find a way to reduce or beautify bit checks on table entries
>> * Storage key support for split pages (will be a separate bugfix)
>> * Regression testing
>> * Testing large setups
>> * Testing multi level VSIE
>>
>> V2:
>> 	* Incorporated changes from David's cleanup
>> 	* Now flushing with IDTE_NODAT for protection transfers.
>> 	* Added RRBE huge page handling for g2 -> g3 skey emulation
>> 	* Added documentation for capability
>> 	* Renamed GMAP_ENTRY_* constants
>> 	* Added SEGMENT hardware bits constants
>> 	* Improved some patch descriptions
>> 	* General small improvements
>> 	* Introduced pte_from_pmd function
>>
>> Accomplished testing:
>> l2: KVM guest
>> l3: nested KVM guest
>>
>> * 1m l2 guests
>> * VSIE (l3) 4k and 1m guests on 1m l2
>> * 1m l2 -> l2 migration with 4k/1m l3 guests
>> * l3 -> l2 migration
>> * postcopy works every second try, seems to be QEMU or my setup
>>
>>
>> The initial prototype was started by Dominik Dingel. I had the
>> pleasure of adding the VSIE part, the protection transfers and the
>> optimizations. A huge thanks to Christian and Martin who review(ed)
>> and helped debugging/designing.
>>
>> Dominik Dingel (2):
>>   s390/mm: hugetlb pages within a gmap can not be freed
>>   s390/mm: clear huge page storage keys on enable_skey
>>
>> Janosch Frank (20):
>>   s390/mm: make gmap_protect_range more modular
>>   s390/mm: Abstract gmap notify bit setting
>>   s390/mm: add gmap PMD invalidation notification
>>   s390/mm: Add gmap pmd invalidation and clearing
>>   s390/mm: Introduce gmap_pmdp_xchg
>>   RFC: s390/mm: Transfer guest pmd protection to host
>>   s390/mm: Add huge page dirty sync support
>>   s390/mm: Add huge pmd storage key handling
>>   s390/mm: Remove superfluous parameter
>>   s390/mm: Add gmap_protect_large read protection support
>>   s390/mm: Make gmap_read_table EDAT1 compatible
>>   s390/mm: Make protect_rmap EDAT1 compatible
>>   s390/mm: GMAP read table extensions
>>   s390/mm: Add shadow segment code
>>   s390/mm: Add VSIE reverse fake case
>>   s390/mm: Remove gmap_pte_op_walk
>>   s390/mm: Split huge pages if granular protection is needed
>>   s390/mm: Enable gmap huge pmd support
>>   KVM: s390: Add KVM HPAGE capability
>>   RFC: s390/mm: Add gmap lock classes
>>
>>  Documentation/virtual/kvm/api.txt |   10 +
>>  arch/s390/include/asm/gmap.h      |   39 +-
>>  arch/s390/include/asm/pgtable.h   |   18 +-
>>  arch/s390/kvm/gaccess.c           |   64 +-
>>  arch/s390/kvm/kvm-s390.c          |   19 +-
>>  arch/s390/mm/fault.c              |   10 +-
>>  arch/s390/mm/gmap.c               | 1275 +++++++++++++++++++++++++++++++++----
>>  arch/s390/mm/pageattr.c           |    6 +-
>>  arch/s390/mm/pgtable.c            |  176 ++++-
>>  include/uapi/linux/kvm.h          |    1 +
>>  10 files changed, 1445 insertions(+), 173 deletions(-)
>>
> 


-- 

Thanks,

David / dhildenb