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

[Paolo Bonzini]

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?

Thanks,