linux-kernel - Re: [PATCH v2 14/15] KVM: x86/tdp

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Date: Fri, 7 Jun 2024 11:03:25 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: seanjc@...gle.com, kvm@...r.kernel.org, kai.huang@...el.com, 
	dmatlack@...gle.com, erdemaktas@...gle.com, isaku.yamahata@...il.com, 
	linux-kernel@...r.kernel.org, sagis@...gle.com, yan.y.zhao@...el.com, 
	Sean Christopherson <sean.j.christopherson@...el.com>, Isaku Yamahata <isaku.yamahata@...el.com>
Subject: Re: [PATCH v2 14/15] KVM: x86/tdp_mmu: Invalidate correct roots

On Thu, May 30, 2024 at 11:07 PM Rick Edgecombe
<rick.p.edgecombe@...el.com> wrote:
>
> From: Sean Christopherson <sean.j.christopherson@...el.com>
>
> When invalidating roots, respect the root type passed.
>
> kvm_tdp_mmu_invalidate_roots() is called with different root types. For
> kvm_mmu_zap_all_fast() it only operates on shared roots. But when tearing
> down a VM it needs to invalidate all roots. Check the root type in root
> iterator.

This patch and patch 12 are small enough that they can be merged.

> @@ -1135,6 +1135,7 @@ void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm)
>  void kvm_tdp_mmu_invalidate_roots(struct kvm *kvm,
>                                   enum kvm_process process_types)
>  {
> +       enum kvm_tdp_mmu_root_types root_types = kvm_process_to_root_types(kvm, process_types);

Maybe pass directly enum kvm_tdp_mmu_root_types?

Looking at patch 12:

+ /*
+ * The private page tables doesn't support fast zapping.  The
+ * caller should handle it by other way.
+ */
+ kvm_tdp_mmu_invalidate_roots(kvm, KVM_PROCESS_SHARED);

now that we have separated private-ness and external-ness, it sounds
much better to write:

/*
 * External page tables don't support fast zapping, therefore
 * their mirrors must be invalidated separately by the caller.
 */
kvm_tdp_mmu_invalidate_roots(kvm, KVM_DIRECT_ROOTS);

while kvm_mmu_uninit_tdp_mmu() can pass KVM_ANY_ROOTS. It may also be
worth adding an

if (WARN_ON_ONCE(root_types & KVM_INVALID_ROOTS))
  root_types &= ~KVM_INVALID_ROOTS;

to document the invariants.

Paolo