[PATCH v2 00/10] KVM: Consolidate and optimize MMU notifiers
Paolo Bonzini
pbonzini at redhat.com
Fri Apr 2 13:17:45 BST 2021
On 02/04/21 02:56, Sean Christopherson wrote:
> The end goal of this series is to optimize the MMU notifiers to take
> mmu_lock if and only if the notification is relevant to KVM, i.e. the hva
> range overlaps a memslot. Large VMs (hundreds of vCPUs) are very
> sensitive to mmu_lock being taken for write at inopportune times, and
> such VMs also tend to be "static", e.g. backed by HugeTLB with minimal
> page shenanigans. The vast majority of notifications for these VMs will
> be spurious (for KVM), and eliding mmu_lock for spurious notifications
> avoids an otherwise unacceptable disruption to the guest.
>
> To get there without potentially degrading performance, e.g. due to
> multiple memslot lookups, especially on non-x86 where the use cases are
> largely unknown (from my perspective), first consolidate the MMU notifier
> logic by moving the hva->gfn lookups into common KVM.
>
> Based on kvm/queue, commit 5f986f748438 ("KVM: x86: dump_vmcs should
> include the autoload/autostore MSR lists").
>
> Well tested on Intel and AMD. Compile tested for arm64, MIPS, PPC,
> PPC e500, and s390. Absolutely needs to be tested for real on non-x86,
> I give it even odds that I introduced an off-by-one bug somewhere.
>
> v2:
> - Drop the patches that have already been pushed to kvm/queue.
> - Drop two selftest changes that had snuck in via "git commit -a".
> - Add a patch to assert that mmu_notifier_count is elevated when
> .change_pte() runs. [Paolo]
> - Split out moving KVM_MMU_(UN)LOCK() to __kvm_handle_hva_range() to a
> separate patch. Opted not to squash it with the introduction of the
> common hva walkers (patch 02), as that prevented sharing code between
> the old and new APIs. [Paolo]
> - Tweak the comment in kvm_vm_destroy() above the smashing of the new
> slots lock. [Paolo]
> - Make mmu_notifier_slots_lock unconditional to avoid #ifdefs. [Paolo]
>
> v1:
> - https://lkml.kernel.org/r/20210326021957.1424875-1-seanjc@google.com
>
> Sean Christopherson (10):
> KVM: Assert that notifier count is elevated in .change_pte()
> KVM: Move x86's MMU notifier memslot walkers to generic code
> KVM: arm64: Convert to the gfn-based MMU notifier callbacks
> KVM: MIPS/MMU: Convert to the gfn-based MMU notifier callbacks
> KVM: PPC: Convert to the gfn-based MMU notifier callbacks
> KVM: Kill off the old hva-based MMU notifier callbacks
> KVM: Move MMU notifier's mmu_lock acquisition into common helper
> KVM: Take mmu_lock when handling MMU notifier iff the hva hits a
> memslot
> KVM: Don't take mmu_lock for range invalidation unless necessary
> KVM: x86/mmu: Allow yielding during MMU notifier unmap/zap, if
> possible
>
> arch/arm64/kvm/mmu.c | 117 +++------
> arch/mips/kvm/mmu.c | 97 ++------
> arch/powerpc/include/asm/kvm_book3s.h | 12 +-
> arch/powerpc/include/asm/kvm_ppc.h | 9 +-
> arch/powerpc/kvm/book3s.c | 18 +-
> arch/powerpc/kvm/book3s.h | 10 +-
> arch/powerpc/kvm/book3s_64_mmu_hv.c | 98 ++------
> arch/powerpc/kvm/book3s_64_mmu_radix.c | 25 +-
> arch/powerpc/kvm/book3s_hv.c | 12 +-
> arch/powerpc/kvm/book3s_pr.c | 56 ++---
> arch/powerpc/kvm/e500_mmu_host.c | 27 +-
> arch/x86/kvm/mmu/mmu.c | 127 ++++------
> arch/x86/kvm/mmu/tdp_mmu.c | 245 +++++++------------
> arch/x86/kvm/mmu/tdp_mmu.h | 14 +-
> include/linux/kvm_host.h | 22 +-
> virt/kvm/kvm_main.c | 325 +++++++++++++++++++------
> 16 files changed, 552 insertions(+), 662 deletions(-)
>
For MIPS, I am going to post a series that simplifies TLB flushing
further. I applied it, and rebased this one on top, to
kvm/mmu-notifier-queue.
Architecture maintainers, please look at the branch and review/test/ack
your parts.
Thanks!
Paolo
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