linux-kernel - Re: [PATCH v2 00/15] KVM: Dynamically size memslot arrays

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Date:   Wed, 23 Oct 2019 20:56:38 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        James Hogan <jhogan@...nel.org>,
        Paul Mackerras <paulus@...abs.org>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Marc Zyngier <maz@...nel.org>
Cc:     David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-mips@...r.kernel.org, kvm-ppc@...r.kernel.org,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
        Marc Zyngier <Marc.Zyngier@....com>
Subject: Re: [PATCH v2 00/15] KVM: Dynamically size memslot arrays



On 22.10.19 15:59, Paolo Bonzini wrote:
> On 22/10/19 02:35, Sean Christopherson wrote:
>> The end goal of this series is to dynamically size the memslot array so
>> that KVM allocates memory based on the number of memslots in use, as
>> opposed to unconditionally allocating memory for the maximum number of
>> memslots.  On x86, each memslot consumes 88 bytes, and so with 2 address
>> spaces of 512 memslots, each VM consumes ~90k bytes for the memslots.
>> E.g. given a VM that uses a total of 30 memslots, dynamic sizing reduces
>> the memory footprint from 90k to ~2.6k bytes.
>>
>> The changes required to support dynamic sizing are relatively small,
>> e.g. are essentially contained in patches 12/13 and 13/13.  Patches 1-11
>> clean up the memslot code, which has gotten quite crusy, especially
>> __kvm_set_memory_region().  The clean up is likely not strictly necessary
>> to switch to dynamic sizing, but I didn't have a remotely reasonable
>> level of confidence in the correctness of the dynamic sizing without first
>> doing the clean up.
>>
>> Testing, especially non-x86 platforms, would be greatly appreciated.  The
>> non-x86 changes are for all intents and purposes untested, e.g. I compile
>> tested pieces of the code by copying them into x86, but that's it.  In
>> theory, the vast majority of the functional changes are arch agnostic, in
>> theory...
>>
>> v2:
>>   - Split "Drop kvm_arch_create_memslot()" into three patches to move
>>     minor functional changes to standalone patches [Janosch].
>>   - Rebase to latest kvm/queue (f0574a1cea5b, "KVM: x86: fix ...")
>>   - Collect an Acked-by and a Reviewed-by
>>
>> Sean Christopherson (15):
>>   KVM: Reinstall old memslots if arch preparation fails
>>   KVM: Don't free new memslot if allocation of said memslot fails
>>   KVM: PPC: Move memslot memory allocation into prepare_memory_region()
>>   KVM: x86: Allocate memslot resources during prepare_memory_region()
>>   KVM: Drop kvm_arch_create_memslot()
>>   KVM: Explicitly free allocated-but-unused dirty bitmap
>>   KVM: Refactor error handling for setting memory region
>>   KVM: Move setting of memslot into helper routine
>>   KVM: Move memslot deletion to helper function
>>   KVM: Simplify kvm_free_memslot() and all its descendents
>>   KVM: Clean up local variable usage in __kvm_set_memory_region()
>>   KVM: Provide common implementation for generic dirty log functions
>>   KVM: Ensure validity of memslot with respect to kvm_get_dirty_log()
>>   KVM: Terminate memslot walks via used_slots
>>   KVM: Dynamically size memslot array based on number of used slots
>>
>>  arch/mips/include/asm/kvm_host.h      |   2 +-
>>  arch/mips/kvm/mips.c                  |  68 +---
>>  arch/powerpc/include/asm/kvm_ppc.h    |  14 +-
>>  arch/powerpc/kvm/book3s.c             |  22 +-
>>  arch/powerpc/kvm/book3s_hv.c          |  36 +-
>>  arch/powerpc/kvm/book3s_pr.c          |  20 +-
>>  arch/powerpc/kvm/booke.c              |  17 +-
>>  arch/powerpc/kvm/powerpc.c            |  13 +-
>>  arch/s390/include/asm/kvm_host.h      |   2 +-
>>  arch/s390/kvm/kvm-s390.c              |  21 +-
>>  arch/x86/include/asm/kvm_page_track.h |   3 +-
>>  arch/x86/kvm/page_track.c             |  15 +-
>>  arch/x86/kvm/x86.c                    | 100 ++---
>>  include/linux/kvm_host.h              |  48 +--
>>  virt/kvm/arm/arm.c                    |  47 +--
>>  virt/kvm/arm/mmu.c                    |  18 +-
>>  virt/kvm/kvm_main.c                   | 546 ++++++++++++++++----------
>>  17 files changed, 467 insertions(+), 525 deletions(-)
>>
> 
> Christian, Marc, Paul, can you help testing patches 1-13?

I see no obvious breakage on s390, but I will do some more testing in the next days.