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Subject[RFC 04/19] KVM: x86/mmu: Yield while processing disconnected_sps
From
When preparing to free disconnected SPs, the list can accumulate many
entries; enough that it is likely necessary to yeild while queuing RCU
callbacks to free the SPs.

Signed-off-by: Ben Gardon <bgardon@google.com>
---
arch/x86/kvm/mmu/tdp_mmu.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index a448f0f2d993..c2a9f7acf8ef 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -513,7 +513,8 @@ static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
* being removed from the paging structure and this function being called.
*/
static void handle_disconnected_sps(struct kvm *kvm,
- struct list_head *disconnected_sps)
+ struct list_head *disconnected_sps,
+ bool can_yield, bool shared)
{
struct kvm_mmu_page *sp;
struct kvm_mmu_page *next;
@@ -521,6 +522,16 @@ static void handle_disconnected_sps(struct kvm *kvm,
list_for_each_entry_safe(sp, next, disconnected_sps, link) {
list_del(&sp->link);
call_rcu(&sp->rcu_head, tdp_mmu_free_sp_rcu_callback);
+
+ if (can_yield &&
+ (need_resched() || rwlock_needbreak(&kvm->mmu_lock))) {
+ rcu_read_unlock();
+ if (shared)
+ cond_resched_rwlock_read(&kvm->mmu_lock);
+ else
+ cond_resched_rwlock_write(&kvm->mmu_lock);
+ rcu_read_lock();
+ }
}
}

@@ -599,7 +610,7 @@ static inline bool tdp_mmu_zap_spte_atomic(struct kvm *kvm,
*/
WRITE_ONCE(*rcu_dereference(iter->sptep), 0);

- handle_disconnected_sps(kvm, &disconnected_sps);
+ handle_disconnected_sps(kvm, &disconnected_sps, false, true);

return true;
}
@@ -817,7 +828,8 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,

if (!list_empty(&disconnected_sps)) {
kvm_flush_remote_tlbs(kvm);
- handle_disconnected_sps(kvm, &disconnected_sps);
+ handle_disconnected_sps(kvm, &disconnected_sps,
+ can_yield, shared);
flush = false;
}

--
2.34.0.rc0.344.g81b53c2807-goog
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