linux-kernel - Re: [PATCH 0/8] KVM: x86/mmu: Allow TDP MMU (un)load to run in parallel

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Date: Thu, 22 Feb 2024 17:35:46 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	David Matlack <dmatlack@...gle.com>, Pattara Teerapong <pteerapong@...gle.com>
Subject: Re: [PATCH 0/8] KVM: x86/mmu: Allow TDP MMU (un)load to run in parallel

On Wed, 10 Jan 2024 18:00:40 -0800, Sean Christopherson wrote:
> This series is the result of digging into why deleting a memslot, which on
> x86 forces all vCPUs to reload a new MMU root, causes noticeably more jitter
> in vCPUs and other tasks when running with the TDP MMU than the Shadow MMU
> (with TDP enabled).
> 
> Patch 1 addresses the most obvious issue by simply zapping at a finer
> granularity so that if a different task, e.g. a vCPU, wants to run on the
> pCPU doing the zapping, it doesn't have to wait for KVM to zap an entire
> 1GiB region, which can take a hundreds of microseconds (or more).  The
> shadow MMU checks for need_resched() (and mmu_lock contention, see below)
> every 10 zaps, which is why the shadow MMU doesn't induce the same level
> of jitter.
> 
> [...]

Applied to kvm-x86 mmu, thanks!

[1/8] KVM: x86/mmu: Zap invalidated TDP MMU roots at 4KiB granularity
      https://github.com/kvm-x86/linux/commit/8ca983631f3c
[2/8] KVM: x86/mmu: Don't do TLB flush when zappings SPTEs in invalid roots
      https://github.com/kvm-x86/linux/commit/fcdffe97f80e
[3/8] KVM: x86/mmu: Allow passing '-1' for "all" as_id for TDP MMU iterators
      https://github.com/kvm-x86/linux/commit/6577f1efdff4
[4/8] KVM: x86/mmu: Skip invalid roots when zapping leaf SPTEs for GFN range
      https://github.com/kvm-x86/linux/commit/99b85fda91b1
[5/8] KVM: x86/mmu: Skip invalid TDP MMU roots when write-protecting SPTEs
      https://github.com/kvm-x86/linux/commit/d746182337c2
[6/8] KVM: x86/mmu: Check for usable TDP MMU root while holding mmu_lock for read
      https://github.com/kvm-x86/linux/commit/f5238c2a60f1
[7/8] KVM: x86/mmu: Alloc TDP MMU roots while holding mmu_lock for read
      https://github.com/kvm-x86/linux/commit/dab285e4ec73
[8/8] KVM: x86/mmu: Free TDP MMU roots while holding mmy_lock for read
      https://github.com/kvm-x86/linux/commit/576a15de8d29

--
https://github.com/kvm-x86/linux/tree/next