On Mon, 7 Nov 2022 21:56:30 +0000, Oliver Upton wrote:
> Presently KVM only takes a read lock for stage 2 faults if it believes
> the fault can be fixed by relaxing permissions on a PTE (write unprotect
> for dirty logging). Otherwise, stage 2 faults grab the write lock, which
> predictably can pile up all the vCPUs in a sufficiently large VM.
>
> Like the TDP MMU for x86, this series loosens the locking around
> manipulations of the stage 2 page tables to allow parallel faults. RCU
> and atomics are exploited to safely build/destroy the stage 2 page
> tables in light of multiple software observers.
>
> [...]
I've gone over this for quite a while, and while I'm still sh*t
scared about it, I've decided to let it simmer in -next for a bit.
If anything goes wrong or that someone spots something ugly,
it will be easy to simply drop the branch. For simple fixes, they
can go on top.
[01/14] KVM: arm64: Combine visitor arguments into a context structure
commit: dfc7a7769ab7f2a2f629c673717ef1fa7b63aa42
[02/14] KVM: arm64: Stash observed pte value in visitor context
commit: 83844a2317ecad935f6735abd854e4bf3f757040
[03/14] KVM: arm64: Pass mm_ops through the visitor context
commit: 2a611c7f87f26cca405da63a57f06d0e4dc14240
[04/14] KVM: arm64: Don't pass kvm_pgtable through kvm_pgtable_walk_data
commit: fa002e8e79b3f980455ba585c1f47b26680de5b9
[05/14] KVM: arm64: Add a helper to tear down unlinked stage-2 subtrees
commit: 8e94e1252cc054bb31fd3e9a15235cd831970ec1
[06/14] KVM: arm64: Use an opaque type for pteps
commit: 6b91b8f95cadd3441c056182daf9024475ac4a91
[07/14] KVM: arm64: Tear down unlinked stage-2 subtree after break-before-make
commit: 5c359cca1faf6d7671537fe1c240e8668467864d
[08/14] KVM: arm64: Protect stage-2 traversal with RCU
commit: c3119ae45dfb6038ca458ab5ba7a9fba2810845b
[09/14] KVM: arm64: Atomically update stage 2 leaf attributes in parallel walks
commit: ca5de2448c3b4c018fe3d6223df8b59068be1cd7
[10/14] KVM: arm64: Split init and set for table PTE
commit: 331aa3a0547d1c794587e0df374d13b16645e832
[11/14] KVM: arm64: Make block->table PTE changes parallel-aware
commit: 0ab12f3574db6cb432917a667f9392a88e8f0dfc
[12/14] KVM: arm64: Make leaf->leaf PTE changes parallel-aware
commit: 946fbfdf336b811479e024136c7cabc00157b6b9
[13/14] KVM: arm64: Make table->block changes parallel-aware
commit: af87fc03cfdf6893011df419588d27acdfb9c197
[14/14] KVM: arm64: Handle stage-2 faults in parallel
commit: 1577cb5823cefdff4416f272a88143ee933d97f5
Fingers crossed,
M.
--
Without deviation from the norm, progress is not possible.
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