Re: [PATCH v8 01/11] KVM: Remove kvm_handle_hva_range helper functions

[Sean Christopherson <seanjc@google.com>]

On Tue, Nov 05, 2024, James Houghton wrote:
> kvm_handle_hva_range is only used by the young notifiers. In a later
> patch, it will be even further tied to the young notifiers. Instead of
> renaming kvm_handle_hva_range to something like

When referencing functions, include parantheses so its super obvious that the
symbol is a function(), e.g. kvm_handle_hva_range(), kvm_handle_hva_range_young(),
etc.

> kvm_handle_hva_range_young, simply remove kvm_handle_hva_range. This
> seems slightly more readable, 

I disagree, quite strongly in fact.  The amount of duplication makes it harder
to see the differences between the three aging flow, and the fewer instances of
this pattern:

	return kvm_handle_hva_range(kvm, &range).ret;

the better.  I added the tuple return as a way to avoid an out-param (which I
still think is a good tradeoff), but there's definitely a cost to it.

> though there is slightly more code duplication.

Heh, you have a different definition of "slightly".  The total lines of code may
be close to a wash, but at the end of the series there's ~10 lines of code that
is nearly identical in three different places.

My vote is for this:

---
 virt/kvm/kvm_main.c | 27 +++++++++++++--------------
 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index de2c11dae231..bf4670e9fcc6 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -551,8 +551,8 @@ static void kvm_null_fn(void)
 	     node;							     \
 	     node = interval_tree_iter_next(node, start, last))	     \
 
-static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm,
-							   const struct kvm_mmu_notifier_range *range)
+static __always_inline kvm_mn_ret_t kvm_handle_hva_range(struct kvm *kvm,
+							 const struct kvm_mmu_notifier_range *range)
 {
 	struct kvm_mmu_notifier_return r = {
 		.ret = false,
@@ -628,7 +628,7 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm,
 	return r;
 }
 
-static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn,
+static __always_inline int kvm_age_hva_range(struct mmu_notifier *mn,
 						unsigned long start,
 						unsigned long end,
 						gfn_handler_t handler,
@@ -647,10 +647,10 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn,
 	return __kvm_handle_hva_range(kvm, &range).ret;
 }
 
-static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn,
-							 unsigned long start,
-							 unsigned long end,
-							 gfn_handler_t handler)
+static __always_inline int kvm_age_hva_range_no_flush(struct mmu_notifier *mn,
+						      unsigned long start,
+						      unsigned long end,
+						      gfn_handler_t handler)
 {
 	return kvm_handle_hva_range(mn, start, end, handler, false);
 }
@@ -747,7 +747,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
 	 * that guest memory has been reclaimed.  This needs to be done *after*
 	 * dropping mmu_lock, as x86's reclaim path is slooooow.
 	 */
-	if (__kvm_handle_hva_range(kvm, &hva_range).found_memslot)
+	if (kvm_handle_hva_range(kvm, &hva_range).found_memslot)
 		kvm_arch_guest_memory_reclaimed(kvm);
 
 	return 0;
@@ -793,7 +793,7 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
 	};
 	bool wake;
 
-	__kvm_handle_hva_range(kvm, &hva_range);
+	kvm_handle_hva_range(kvm, &hva_range);
 
 	/* Pairs with the increment in range_start(). */
 	spin_lock(&kvm->mn_invalidate_lock);
@@ -817,8 +817,8 @@ static int kvm_mmu_notifier_clear_flush_young(struct mmu_notifier *mn,
 {
 	trace_kvm_age_hva(start, end);
 
-	return kvm_handle_hva_range(mn, start, end, kvm_age_gfn,
-				    !IS_ENABLED(CONFIG_KVM_ELIDE_TLB_FLUSH_IF_YOUNG));
+	return kvm_age_hva_range(mn, start, end, kvm_age_gfn,
+				 !IS_ENABLED(CONFIG_KVM_ELIDE_TLB_FLUSH_IF_YOUNG));
 }
 
 static int kvm_mmu_notifier_clear_young(struct mmu_notifier *mn,
@@ -841,7 +841,7 @@ static int kvm_mmu_notifier_clear_young(struct mmu_notifier *mn,
 	 * cadence. If we find this inaccurate, we might come up with a
 	 * more sophisticated heuristic later.
 	 */
-	return kvm_handle_hva_range_no_flush(mn, start, end, kvm_age_gfn);
+	return kvm_age_hva_range_no_flush(mn, start, end, kvm_age_gfn);
 }
 
 static int kvm_mmu_notifier_test_young(struct mmu_notifier *mn,
@@ -850,8 +850,7 @@ static int kvm_mmu_notifier_test_young(struct mmu_notifier *mn,
 {
 	trace_kvm_test_age_hva(address);
 
-	return kvm_handle_hva_range_no_flush(mn, address, address + 1,
-					     kvm_test_age_gfn);
+	return kvm_age_hva_range_no_flush(mn, address, address + 1, kvm_test_age_gfn);
 }
 
 static void kvm_mmu_notifier_release(struct mmu_notifier *mn,

base-commit: 2d5faa6a8402435d6332e8e8f3c3f18cca382d83
--