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

Paolo Bonzini
2019-10-22T13:59:23Z

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,