linux-kernel - Re: [PATCH 1/3] KVM: x86/mmu: Open code walking TDP MMU roots for mmu

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Message-ID: <01cf00ad-0461-d72f-4b0d-d2093628049d@redhat.com>
Date:   Thu, 21 Sep 2023 12:05:14 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pattara Teerapong <pteerapong@...gle.com>,
        David Stevens <stevensd@...gle.com>,
        Yiwei Zhang <zzyiwei@...gle.com>,
        Paul Hsia <paulhsia@...gle.com>
Subject: Re: [PATCH 1/3] KVM: x86/mmu: Open code walking TDP MMU roots for
 mmu_notifier's zap SPTEs

On 9/16/23 02:39, Sean Christopherson wrote:
> Use the "inner" TDP MMU root walker when zapping SPTEs in response to an
> mmu_notifier invalidation instead of invoking kvm_tdp_mmu_zap_leafs().
> This will allow reworking for_each_tdp_mmu_root_yield_safe() to do more
> work, and to also make it usable in more places, without increasing the
> number of params to the point where it adds no value.
> 
> The mmu_notifier path is a bit of a special snowflake, e.g. it zaps only a
> single address space (because it's per-slot), and can't always yield.
> 
> Drop the @can_yield param from tdp_mmu_zap_leafs() as its sole remaining
> caller unconditionally passes "true".

Slightly rewritten commit log:

---
The mmu_notifier path is a bit of a special snowflake, e.g. it zaps only a
single address space (because it's per-slot), and can't always yield.
Because of this, it calls kvm_tdp_mmu_zap_leafs() in ways that no one
else does.

Iterate manually over the leafs in response to an mmu_notifier
invalidation, instead of invoking kvm_tdp_mmu_zap_leafs().  Drop the
@can_yield param from kvm_tdp_mmu_zap_leafs() as its sole remaining
caller unconditionally passes "true".
---

and using the "__" macro can be moved to the second patch.

Paolo