Re: [PATCH 21/28] KVM: x86/mmu: Add TDP MMU helper to zap a root

Ben Gardon
2021-11-22T22:55:16Z

On Fri, Nov 19, 2021 at 8:51 PM Sean Christopherson <seanjc@google.com> wrote:
>
> Add a small wrapper to handle zapping a specific root. For now, it's
> little more than syntactic sugar, but in the future it will become a
> unique flow with rules specific to zapping an unreachable root.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/mmu/tdp_mmu.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 9449cb5baf0b..31fb622249e5 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -79,11 +79,18 @@ static void tdp_mmu_free_sp_rcu_callback(struct rcu_head *head)
> tdp_mmu_free_sp(sp);
> }
>
> +static bool tdp_mmu_zap_root(struct kvm *kvm, struct kvm_mmu_page *root,
> + bool shared)
> +{
> + return zap_gfn_range(kvm, root, 0, -1ull, true, false, shared);

Total aside:
Remembering the order of these three boolean parameters through all
these functions drives me nuts.
It'd be really nice to put them into a neat, reusable struct that tracks:
MMU lock mode (read / write / none)
If yielding is okay
If the TLBs are dirty and need to be flushed

I don't know when I'll have time to do that refactor, but it would
make this code so much more sensible.

> +}
> +
> /*
> * Note, putting a root might sleep, i.e. the caller must have IRQs enabled and
> * must not explicitly disable preemption (it will be disabled by virtue of
> * holding mmu_lock, hence the lack of a might_sleep()).
> */
> +
> void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root,
> bool shared)
> {
> @@ -118,7 +125,7 @@ void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root,
> * should have been zapped by kvm_tdp_mmu_zap_invalidated_roots(), and
> * inserting new SPTEs under an invalid root is a KVM bug.
> */
> - if (zap_gfn_range(kvm, root, 0, -1ull, true, false, shared))
> + if (tdp_mmu_zap_root(kvm, root, shared))
> WARN_ON_ONCE(root->role.invalid);
>
> call_rcu(&root->rcu_head, tdp_mmu_free_sp_rcu_callback);
> @@ -923,7 +930,7 @@ void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm,
> * will still flush on yield, but that's a minor performance
> * blip and not a functional issue.
> */
> - (void)zap_gfn_range(kvm, root, 0, -1ull, true, false, true);
> + (void)tdp_mmu_zap_root(kvm, root, true);
> kvm_tdp_mmu_put_root(kvm, root, true);
> }
> }
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>