Re: [GIT PULL] KVM: x86: MMU changes for 6.9

[Paolo Bonzini]

On 3/8/24 23:36, Sean Christopherson wrote:
> The bulk of the changes are TDP MMU improvements related to memslot deletion
> (ChromeOS has a use case that "requires" frequent deletion of a GPU buffer).
> The other highlight is allocating the write-tracking metadata on-demand, e.g.
> so that distro kernels pay the memory cost of the arrays if and only if KVM
> or KVMGT actually needs to shadow guest page tables.
>
> The following changes since commit 41bccc98fb7931d63d03f326a746ac4d429c1dd3:
>
>    Linux 6.8-rc2 (2024-01-28 17:01:12 -0800)
>
> are available in the Git repository at:
>
>    https://github.com/kvm-x86/linux.git tags/kvm-x86-mmu-6.9
>
> for you to fetch changes up to a364c014a2c1ad6e011bc5fdb8afb9d4ba316956:
>
>    kvm/x86: allocate the write-tracking metadata on-demand (2024-02-27 11:49:54 -0800)

Pulled, thanks.

Paolo

> ----------------------------------------------------------------
> KVM x86 MMU changes for 6.9:
>
>   - Clean up code related to unprotecting shadow pages when retrying a guest
>     instruction after failed #PF-induced emulation.
>
>   - Zap TDP MMU roots at 4KiB granularity to minimize the delay in yielding if
>     a reschedule is needed, e.g. if a high priority task needs to run.  Because
>     KVM doesn't support yielding in the middle of processing a zapped non-leaf
>     SPTE, zapping at 1GiB granularity can result in multi-millisecond lag when
>     attempting to schedule in a high priority.
>
>   - Rework TDP MMU root unload, free, and alloc to run with mmu_lock held for
>     read, e.g. to avoid serializing vCPUs when userspace deletes a memslot.
>
>   - Allocate write-tracking metadata on-demand to avoid the memory overhead when
>     running kernels built with KVMGT support (external write-tracking enabled),
>     but for workloads that don't use nested virtualization (shadow paging) or
>     KVMGT.
>
> ----------------------------------------------------------------
> Andrei Vagin (1):
>        kvm/x86: allocate the write-tracking metadata on-demand
>
> Kunwu Chan (1):
>        KVM: x86/mmu: Use KMEM_CACHE instead of kmem_cache_create()
>
> Mingwei Zhang (1):
>        KVM: x86/mmu: Don't acquire mmu_lock when using indirect_shadow_pages as a heuristic
>
> Sean Christopherson (10):
>        KVM: x86: Drop dedicated logic for direct MMUs in reexecute_instruction()
>        KVM: x86: Drop superfluous check on direct MMU vs. WRITE_PF_TO_SP flag
>        KVM: x86/mmu: Zap invalidated TDP MMU roots at 4KiB granularity
>        KVM: x86/mmu: Don't do TLB flush when zappings SPTEs in invalid roots
>        KVM: x86/mmu: Allow passing '-1' for "all" as_id for TDP MMU iterators
>        KVM: x86/mmu: Skip invalid roots when zapping leaf SPTEs for GFN range
>        KVM: x86/mmu: Skip invalid TDP MMU roots when write-protecting SPTEs
>        KVM: x86/mmu: Check for usable TDP MMU root while holding mmu_lock for read
>        KVM: x86/mmu: Alloc TDP MMU roots while holding mmu_lock for read
>        KVM: x86/mmu: Free TDP MMU roots while holding mmy_lock for read
>
>   arch/x86/include/asm/kvm_host.h |   9 +++
>   arch/x86/kvm/mmu/mmu.c          |  37 +++++++-----
>   arch/x86/kvm/mmu/page_track.c   |  68 +++++++++++++++++++++-
>   arch/x86/kvm/mmu/tdp_mmu.c      | 124 ++++++++++++++++++++++++++++------------
>   arch/x86/kvm/mmu/tdp_mmu.h      |   2 +-
>   arch/x86/kvm/x86.c              |  35 +++++-------
>   6 files changed, 201 insertions(+), 74 deletions(-)