Re: [PATCH v3 01/28] KVM: x86/mmu: Use common iterator for walking invalid TDP MMU roots

Mingwei Zhang
2022-03-02T19:08:20Z

On Sat, Feb 26, 2022, Sean Christopherson wrote:
> Now that tdp_mmu_next_root() can process both valid and invalid roots,
> extend it to be able to process _only_ invalid roots, add yet another
> iterator macro for walking invalid roots, and use the new macro in
> kvm_tdp_mmu_zap_invalidated_roots().
>
> No functional change intended.
>
> Reviewed-by: David Matlack <dmatlack@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/mmu/tdp_mmu.c | 74 ++++++++++++++------------------------
> 1 file changed, 26 insertions(+), 48 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index debf08212f12..25148e8b711d 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -98,6 +98,12 @@ void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root,
> call_rcu(&root->rcu_head, tdp_mmu_free_sp_rcu_callback);
> }
>
> +enum tdp_mmu_roots_iter_type {
> + ALL_ROOTS = -1,
> + VALID_ROOTS = 0,
> + INVALID_ROOTS = 1,
> +};

I am wondering what the trick is to start from -1?
> +
> /*
> * Returns the next root after @prev_root (or the first root if @prev_root is
> * NULL). A reference to the returned root is acquired, and the reference to
> @@ -110,10 +116,16 @@ void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root,
> */
> static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
> struct kvm_mmu_page *prev_root,
> - bool shared, bool only_valid)
> + bool shared,
> + enum tdp_mmu_roots_iter_type type)
> {
> struct kvm_mmu_page *next_root;
>
> + kvm_lockdep_assert_mmu_lock_held(kvm, shared);
> +
> + /* Ensure correctness for the below comparison against role.invalid. */
> + BUILD_BUG_ON(!!VALID_ROOTS || !INVALID_ROOTS);
> +
> rcu_read_lock();
>
> if (prev_root)
> @@ -125,7 +137,7 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
> typeof(*next_root), link);
>
> while (next_root) {
> - if ((!only_valid || !next_root->role.invalid) &&
> + if ((type == ALL_ROOTS || (type == !!next_root->role.invalid)) &&
> kvm_tdp_mmu_get_root(next_root))
> break;
>
> @@ -151,18 +163,21 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
> * mode. In the unlikely event that this thread must free a root, the lock
> * will be temporarily dropped and reacquired in write mode.
> */
> -#define __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, _only_valid)\
> - for (_root = tdp_mmu_next_root(_kvm, NULL, _shared, _only_valid); \
> +#define __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, _type) \
> + for (_root = tdp_mmu_next_root(_kvm, NULL, _shared, _type); \
> _root; \
> - _root = tdp_mmu_next_root(_kvm, _root, _shared, _only_valid)) \
> - if (kvm_mmu_page_as_id(_root) != _as_id) { \
> + _root = tdp_mmu_next_root(_kvm, _root, _shared, _type)) \
> + if (_as_id > 0 && kvm_mmu_page_as_id(_root) != _as_id) { \
> } else
>
> +#define for_each_invalid_tdp_mmu_root_yield_safe(_kvm, _root) \
> + __for_each_tdp_mmu_root_yield_safe(_kvm, _root, -1, true, INVALID_ROOTS)
> +
> #define for_each_valid_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared) \
> - __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, true)
> + __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, VALID_ROOTS)
>
> #define for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared) \
> - __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, false)
> + __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, ALL_ROOTS)
>
> #define for_each_tdp_mmu_root(_kvm, _root, _as_id) \
> list_for_each_entry_rcu(_root, &_kvm->arch.tdp_mmu_roots, link, \
> @@ -810,28 +825,6 @@ void kvm_tdp_mmu_zap_all(struct kvm *kvm)
> kvm_flush_remote_tlbs(kvm);
> }
>
> -static struct kvm_mmu_page *next_invalidated_root(struct kvm *kvm,
> - struct kvm_mmu_page *prev_root)
> -{
> - struct kvm_mmu_page *next_root;
> -
> - if (prev_root)
> - next_root = list_next_or_null_rcu(&kvm->arch.tdp_mmu_roots,
> - &prev_root->link,
> - typeof(*prev_root), link);
> - else
> - next_root = list_first_or_null_rcu(&kvm->arch.tdp_mmu_roots,
> - typeof(*next_root), link);
> -
> - while (next_root && !(next_root->role.invalid &&
> - refcount_read(&next_root->tdp_mmu_root_count)))
> - next_root = list_next_or_null_rcu(&kvm->arch.tdp_mmu_roots,
> - &next_root->link,
> - typeof(*next_root), link);
> -
> - return next_root;
> -}
> -
> /*
> * Since kvm_tdp_mmu_zap_all_fast has acquired a reference to each
> * invalidated root, they will not be freed until this function drops the
> @@ -842,36 +835,21 @@ static struct kvm_mmu_page *next_invalidated_root(struct kvm *kvm,
> */
> void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm)
> {
> - struct kvm_mmu_page *next_root;
> struct kvm_mmu_page *root;
> bool flush = false;
>
> lockdep_assert_held_read(&kvm->mmu_lock);
>
> - rcu_read_lock();
> -
> - root = next_invalidated_root(kvm, NULL);
> -
> - while (root) {
> - next_root = next_invalidated_root(kvm, root);
> -
> - rcu_read_unlock();
> -
> + for_each_invalid_tdp_mmu_root_yield_safe(kvm, root) {
> flush = zap_gfn_range(kvm, root, 0, -1ull, true, flush, true);
>
> /*
> - * Put the reference acquired in
> - * kvm_tdp_mmu_invalidate_roots
> + * Put the reference acquired in kvm_tdp_mmu_invalidate_roots().
> + * Note, the iterator holds its own reference.
> */
> kvm_tdp_mmu_put_root(kvm, root, true);
> -
> - root = next_root;
> -
> - rcu_read_lock();
> }
>
> - rcu_read_unlock();
> -
> if (flush)
> kvm_flush_remote_tlbs(kvm);
> }
> --
> 2.35.1.574.g5d30c73bfb-goog
>