[Patch] KVM: x86/mmu: Make optimized __handle_changed_spte() for clear dirty log

Vipin Sharma
2023-01-25T21:39:11Z

Use a tone down version of __handle_changed_spte() when clearing dirty
log. Remove checks which will not be needed when dirty logs are cleared.

This change shows ~13% improvement in clear dirty log calls in
dirty_log_perf_test

Before tone down version:
Clear dirty log over 3 iterations took 10.006764203s. (Avg 3.335588067s/iteration)

After tone down version:
Clear dirty log over 3 iterations took 8.686433554s. (Avg 2.895477851s/iteration)

Signed-off-by: Vipin Sharma <vipinsh@google.com>
---
arch/x86/kvm/mmu/tdp_mmu.c | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index bba33aea0fb0..ca21b33c4386 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -504,6 +504,19 @@ static void handle_removed_pt(struct kvm *kvm, tdp_ptep_t pt, bool shared)
call_rcu(&sp->rcu_head, tdp_mmu_free_sp_rcu_callback);
}

+static void handle_changed_spte_clear_dirty_log(int as_id, gfn_t gfn,
+ u64 old_spte, u64 new_spte,
+ int level)
+{
+ if (old_spte == new_spte)
+ return;
+
+ trace_kvm_tdp_mmu_spte_changed(as_id, gfn, level, old_spte, new_spte);
+
+ if (is_dirty_spte(old_spte) && !is_dirty_spte(new_spte))
+ kvm_set_pfn_dirty(spte_to_pfn(old_spte));
+}
+
/**
* __handle_changed_spte - handle bookkeeping associated with an SPTE change
* @kvm: kvm instance
@@ -736,7 +749,12 @@ static u64 __tdp_mmu_set_spte(struct kvm *kvm, int as_id, tdp_ptep_t sptep,

old_spte = kvm_tdp_mmu_write_spte(sptep, old_spte, new_spte, level);

- __handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level, false);
+ if (record_dirty_log)
+ __handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte,
+ level, false);
+ else
+ handle_changed_spte_clear_dirty_log(as_id, gfn, old_spte,
+ new_spte, level);

if (record_acc_track)
handle_changed_spte_acc_track(old_spte, new_spte, level);
--
2.39.1.456.gfc5497dd1b-goog