linux-kernel - [PATCH v4 12/13] KVM: x86/mmu: Remove handle_changed_spte_dirty

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Date:   Tue, 21 Mar 2023 15:00:20 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vipin Sharma <vipinsh@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH v4 12/13] KVM: x86/mmu: Remove handle_changed_spte_dirty_log()

From: Vipin Sharma <vipinsh@...gle.com>

Remove handle_changed_spte_dirty_log() as there is no code flow which
sets 4KiB SPTE writable and hit this path. This function marks the page
dirty in a memslot only if new SPTE is 4KiB in size and writable.

Current users of handle_changed_spte_dirty_log() are:
1. set_spte_gfn() - Create only non writable SPTEs.
2. write_protect_gfn() - Change an SPTE to non writable.
3. zap leaf and roots APIs - Everything is 0.
4. handle_removed_pt() - Sets SPTEs to REMOVED_SPTE
5. tdp_mmu_link_sp() - Makes non leaf SPTEs.

There is also no path which creates a writable 4KiB without going
through make_spte() and this functions takes care of marking SPTE dirty
in the memslot if it is PT_WRITABLE.

Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
Reviewed-by: David Matlack <dmatlack@...gle.com>
[sean: add blurb to __handle_changed_spte()'s comment]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 26 +++-----------------------
 1 file changed, 3 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 9649e0fe4302..e8ee49b6da5b 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -345,24 +345,6 @@ static void handle_changed_spte_acc_track(u64 old_spte, u64 new_spte, int level)
 		kvm_set_pfn_accessed(spte_to_pfn(old_spte));
 }
 
-static void handle_changed_spte_dirty_log(struct kvm *kvm, int as_id, gfn_t gfn,
-					  u64 old_spte, u64 new_spte, int level)
-{
-	bool pfn_changed;
-	struct kvm_memory_slot *slot;
-
-	if (level > PG_LEVEL_4K)
-		return;
-
-	pfn_changed = spte_to_pfn(old_spte) != spte_to_pfn(new_spte);
-
-	if ((!is_writable_pte(old_spte) || pfn_changed) &&
-	    is_writable_pte(new_spte)) {
-		slot = __gfn_to_memslot(__kvm_memslots(kvm, as_id), gfn);
-		mark_page_dirty_in_slot(kvm, slot, gfn);
-	}
-}
-
 static void tdp_account_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp)
 {
 	kvm_account_pgtable_pages((void *)sp->spt, +1);
@@ -516,7 +498,9 @@ static void handle_removed_pt(struct kvm *kvm, tdp_ptep_t pt, bool shared)
  *	    the MMU lock and the operation must synchronize with other
  *	    threads that might be modifying SPTEs.
  *
- * Handle bookkeeping that might result from the modification of a SPTE.
+ * Handle bookkeeping that might result from the modification of a SPTE.  Note,
+ * dirty logging updates are handled in common code, not here (see make_spte()
+ * and fast_pf_fix_direct_spte()).
  */
 static void __handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
 				  u64 old_spte, u64 new_spte, int level,
@@ -613,8 +597,6 @@ static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
 	__handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level,
 			      shared);
 	handle_changed_spte_acc_track(old_spte, new_spte, level);
-	handle_changed_spte_dirty_log(kvm, as_id, gfn, old_spte,
-				      new_spte, level);
 }
 
 /*
@@ -725,8 +707,6 @@ static u64 tdp_mmu_set_spte(struct kvm *kvm, int as_id, tdp_ptep_t sptep,
 
 	__handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level, false);
 	handle_changed_spte_acc_track(old_spte, new_spte, level);
-	handle_changed_spte_dirty_log(kvm, as_id, gfn, old_spte, new_spte,
-				      level);
 	return old_spte;
 }
 
-- 
2.40.0.rc2.332.ga46443480c-goog