Re: [PATCH 00/28] KVM: x86/mmu: Overhaul TDP MMU zapping and flushing

David Matlack
2021-12-01T17:54:36Z

On Fri, Nov 19, 2021 at 8:51 PM Sean Christopherson <seanjc@google.com> wrote:
>
> Overhaul TDP MMU's handling of zapping and TLB flushing to reduce the
> number of TLB flushes, and to clean up the zapping code. The final patch
> realizes the biggest change, which is to use RCU to defer any TLB flush
> due to zapping a SP to the caller. The largest cleanup is to separate the
> flows for zapping roots (zap _everything_), zapping leaf SPTEs (zap guest
> mappings for whatever reason), and zapping a specific SP (NX recovery).
> They're currently smushed into a single zap_gfn_range(), which was a good
> idea at the time, but became a mess when trying to handle the different
> rules, e.g. TLB flushes aren't needed when zapping a root because KVM can
> safely zap a root if and only if it's unreachable.
>
> For booting an 8 vCPU, remote_tlb_flush (requests) goes from roughly
> 180 (600) to 130 (215).
>
> Please don't apply patches 02 and 03, they've been posted elsehwere and by
> other people. I included them here because some of the patches have
> pseudo-dependencies on their changes. Patch 01 is also posted separately.
> I had a brain fart and sent it out realizing that doing so would lead to
> oddities.

What's the base commit for this series?

>
> Hou Wenlong (1):
> KVM: x86/mmu: Skip tlb flush if it has been done in zap_gfn_range()
>
> Sean Christopherson (27):
> KVM: x86/mmu: Use yield-safe TDP MMU root iter in MMU notifier
> unmapping
> KVM: x86/mmu: Remove spurious TLB flushes in TDP MMU zap collapsible
> path
> KVM: x86/mmu: Retry page fault if root is invalidated by memslot
> update
> KVM: x86/mmu: Check for present SPTE when clearing dirty bit in TDP
> MMU
> KVM: x86/mmu: Formalize TDP MMU's (unintended?) deferred TLB flush
> logic
> KVM: x86/mmu: Document that zapping invalidated roots doesn't need to
> flush
> KVM: x86/mmu: Drop unused @kvm param from kvm_tdp_mmu_get_root()
> KVM: x86/mmu: Require mmu_lock be held for write in unyielding root
> iter
> KVM: x86/mmu: Allow yielding when zapping GFNs for defunct TDP MMU
> root
> KVM: x86/mmu: Check for !leaf=>leaf, not PFN change, in TDP MMU SP
> removal
> KVM: x86/mmu: Batch TLB flushes from TDP MMU for MMU notifier
> change_spte
> KVM: x86/mmu: Drop RCU after processing each root in MMU notifier
> hooks
> KVM: x86/mmu: Add helpers to read/write TDP MMU SPTEs and document RCU
> KVM: x86/mmu: Take TDP MMU roots off list when invalidating all roots
> KVM: x86/mmu: WARN if old _or_ new SPTE is REMOVED in non-atomic path
> KVM: x86/mmu: Terminate yield-friendly walk if invalid root observed
> KVM: x86/mmu: Refactor low-level TDP MMU set SPTE helper to take raw
> vals
> KVM: x86/mmu: Zap only the target TDP MMU shadow page in NX recovery
> KVM: x86/mmu: Use common TDP MMU zap helper for MMU notifier unmap
> hook
> KVM: x86/mmu: Add TDP MMU helper to zap a root
> KVM: x86/mmu: Skip remote TLB flush when zapping all of TDP MMU
> KVM: x86/mmu: Use "zap root" path for "slow" zap of all TDP MMU SPTEs
> KVM: x86/mmu: Add dedicated helper to zap TDP MMU root shadow page
> KVM: x86/mmu: Require mmu_lock be held for write to zap TDP MMU range
> KVM: x86/mmu: Zap only TDP MMU leafs in kvm_zap_gfn_range()
> KVM: x86/mmu: Do remote TLB flush before dropping RCU in TDP MMU
> resched
> KVM: x86/mmu: Defer TLB flush to caller when freeing TDP MMU shadow
> pages
>
> arch/x86/kvm/mmu/mmu.c | 74 +++--
> arch/x86/kvm/mmu/mmu_internal.h | 7 +-
> arch/x86/kvm/mmu/paging_tmpl.h | 3 +-
> arch/x86/kvm/mmu/tdp_iter.c | 6 +-
> arch/x86/kvm/mmu/tdp_iter.h | 15 +-
> arch/x86/kvm/mmu/tdp_mmu.c | 526 +++++++++++++++++++-------------
> arch/x86/kvm/mmu/tdp_mmu.h | 48 +--
> 7 files changed, 406 insertions(+), 273 deletions(-)
>
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>