[PATCH 0/3] KVM: selftests: Delete three pieces of dead library code

[PATCH 0/3] KVM: selftests: Delete three pieces of dead library code

[Gokul K]

Three unused things in the selftest library, found by asking the linker
rather than by reading: build the selftests, then look for global symbols
in lib/ that no object refers to, and check each survivor against the
whole source tree by hand.

  1/3  sparsebit_copy() and sparsebit_num_set(), neither called
  2/3  the declaration of vcpu_set_cpuid_maxphyaddr(), which has no
       definition anywhere
  3/3  guest_snprintf(), a varargs wrapper nobody calls

Each is independent and they can be taken in any order.

A note on what is deliberately *not* here, because the same scan turns it
up and the obvious next step is wrong. sparsebit.c still exports nine more
functions that no caller outside the file uses - sparsebit_all_set(),
sparsebit_is_clear(), sparsebit_validate_internal() and friends. They are
not dead: they are called from inside sparsebit.c, mostly from the
assertions in sparsebit_validate_internal() and from asserts in live
functions, so deleting them would not build. Making them static and
dropping their declarations is a defensible follow-up, but it is a change
of intent about what the library exposes rather than a removal of dead
code, so it does not belong in this series.

No functional change intended. Built with and without -Wextra, and a
sample of twelve x86 selftests gives identical results before and after;
kvm_binary_stats_test and the rest still pass. The two that fail here fail
identically without the series, because this host's kernel is older than
the tree.

Gokul K (3):
  KVM: selftests: Delete the unused sparsebit copy and count helpers
  KVM: selftests: Delete the declaration of vcpu_set_cpuid_maxphyaddr()
  KVM: selftests: Delete the unused guest_snprintf()

 tools/testing/selftests/kvm/include/sparsebit.h    |  2 -
 tools/testing/selftests/kvm/include/test_util.h    |  1 -
 .../testing/selftests/kvm/include/x86/processor.h  |  1 -
 tools/testing/selftests/kvm/lib/guest_sprintf.c    | 12 -----
 tools/testing/selftests/kvm/lib/sparsebit.c        | 63 +---------------------
 5 files changed, 1 insertion(+), 78 deletions(-)

-- 
2.51.0

[PATCH 1/3] KVM: selftests: Delete the unused sparsebit copy and count helpers

[Gokul K]

sparsebit_copy() and sparsebit_num_set() have no callers.  Nor does the
FUZZ harness at the bottom of lib/sparsebit.c, which exercises most of
the rest of the API and still builds and links with both removed.

sparsebit_copy() was the only non-recursive caller of
node_copy_subtree(), which leaves that unreachable too.  It is static,
so keeping it would trip -Wunused-function; delete it as well.

The comment on the num_set member gives sparsebit_num_set() as the
reason the count is maintained.  The member stays - it is what lets
sparsebit_all_set() answer in O(1), and the dump path prints it - so
point the comment at what still uses it.

No functional change intended.

Signed-off-by: Gokul K <gokul02k@gmail.com>
---
 .../testing/selftests/kvm/include/sparsebit.h |  2 -
 tools/testing/selftests/kvm/lib/sparsebit.c   | 63 +------------------
 2 files changed, 1 insertion(+), 64 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/sparsebit.h b/tools/testing/selftests/kvm/include/sparsebit.h
index e027e5790946..8a2ab11dae6f 100644
--- a/tools/testing/selftests/kvm/include/sparsebit.h
+++ b/tools/testing/selftests/kvm/include/sparsebit.h
@@ -30,7 +30,6 @@ typedef u64 sparsebit_num_t;
 
 struct sparsebit *sparsebit_alloc(void);
 void sparsebit_free(struct sparsebit **sbitp);
-void sparsebit_copy(struct sparsebit *dstp, const struct sparsebit *src);
 
 bool sparsebit_is_set(const struct sparsebit *sbit, sparsebit_idx_t idx);
 bool sparsebit_is_set_num(const struct sparsebit *sbit,
@@ -38,7 +37,6 @@ bool sparsebit_is_set_num(const struct sparsebit *sbit,
 bool sparsebit_is_clear(const struct sparsebit *sbit, sparsebit_idx_t idx);
 bool sparsebit_is_clear_num(const struct sparsebit *sbit,
 			    sparsebit_idx_t idx, sparsebit_num_t num);
-sparsebit_num_t sparsebit_num_set(const struct sparsebit *sbit);
 bool sparsebit_any_set(const struct sparsebit *sbit);
 bool sparsebit_any_clear(const struct sparsebit *sbit);
 bool sparsebit_all_set(const struct sparsebit *sbit);
diff --git a/tools/testing/selftests/kvm/lib/sparsebit.c b/tools/testing/selftests/kvm/lib/sparsebit.c
index 4d845000de15..8ce230af4f14 100644
--- a/tools/testing/selftests/kvm/lib/sparsebit.c
+++ b/tools/testing/selftests/kvm/lib/sparsebit.c
@@ -184,8 +184,7 @@ struct sparsebit {
 
 	/*
 	 * A redundant count of the total number of bits set.  Used for
-	 * diagnostic purposes and to change the time complexity of
-	 * sparsebit_num_set() from O(n) to O(1).
+	 * diagnostic purposes and to answer sparsebit_all_set() in O(1).
 	 * Note: Due to overflow, a value of 0 means none or all set.
 	 */
 	sparsebit_num_t num_set;
@@ -269,39 +268,6 @@ static struct node *node_prev(const struct sparsebit *s, struct node *np)
 }
 
 
-/* Allocates space to hold a copy of the node sub-tree pointed to by
- * subtree and duplicates the bit settings to the newly allocated nodes.
- * Returns the newly allocated copy of subtree.
- */
-static struct node *node_copy_subtree(const struct node *subtree)
-{
-	struct node *root;
-
-	/* Duplicate the node at the root of the subtree */
-	root = calloc(1, sizeof(*root));
-	if (!root) {
-		perror("calloc");
-		abort();
-	}
-
-	root->idx = subtree->idx;
-	root->mask = subtree->mask;
-	root->num_after = subtree->num_after;
-
-	/* As needed, recursively duplicate the left and right subtrees */
-	if (subtree->left) {
-		root->left = node_copy_subtree(subtree->left);
-		root->left->parent = root;
-	}
-
-	if (subtree->right) {
-		root->right = node_copy_subtree(subtree->right);
-		root->right->parent = root;
-	}
-
-	return root;
-}
-
 /* Searches for and returns a pointer to the node that describes the setting
  * of the bit given by idx.  A node describes the setting of a bit if its
  * index is within the bits described by the mask bits or the number of
@@ -964,22 +930,6 @@ void sparsebit_free(struct sparsebit **sbitp)
 	*sbitp = NULL;
 }
 
-/* Makes a copy of the sparsebit array given by s, to the sparsebit
- * array given by d.  Note, d must have already been allocated via
- * sparsebit_alloc().  It can though already have bits set, which
- * if different from src will be cleared.
- */
-void sparsebit_copy(struct sparsebit *d, const struct sparsebit *s)
-{
-	/* First clear any bits already set in the destination */
-	sparsebit_clear_all(d);
-
-	if (s->root) {
-		d->root = node_copy_subtree(s->root);
-		d->num_set = s->num_set;
-	}
-}
-
 /* Returns whether num consecutive bits starting at idx are all set.  */
 bool sparsebit_is_set_num(const struct sparsebit *s,
 	sparsebit_idx_t idx, sparsebit_num_t num)
@@ -1035,17 +985,6 @@ bool sparsebit_is_clear_num(const struct sparsebit *s,
 	return next_set == 0 || next_set - idx >= num;
 }
 
-/* Returns the total number of bits set.  Note: 0 is also returned for
- * the case of all bits set.  This is because with all bits set, there
- * is 1 additional bit set beyond what can be represented in the return
- * value.  Use sparsebit_any_set(), instead of sparsebit_num_set() > 0,
- * to determine if the sparsebit array has any bits set.
- */
-sparsebit_num_t sparsebit_num_set(const struct sparsebit *s)
-{
-	return s->num_set;
-}
-
 /* Returns whether any bit is set in the sparsebit array.  */
 bool sparsebit_any_set(const struct sparsebit *s)
 {
-- 
2.54.0

Re: [PATCH 1/3] KVM: selftests: Delete the unused sparsebit copy and count helpers

[Sean Christopherson]

On Fri, Sep 18, 2026, Gokul K wrote:
> sparsebit_copy() and sparsebit_num_set() have no callers.  Nor does the
> FUZZ harness at the bottom of lib/sparsebit.c, which exercises most of
> the rest of the API and still builds and links with both removed.
> 
> sparsebit_copy() was the only non-recursive caller of
> node_copy_subtree(), which leaves that unreachable too.  It is static,
> so keeping it would trip -Wunused-function; delete it as well.
> 
> The comment on the num_set member gives sparsebit_num_set() as the
> reason the count is maintained.  The member stays - it is what lets
> sparsebit_all_set() answer in O(1), and the dump path prints it - so
> point the comment at what still uses it.
> 
> No functional change intended.
> 
> Signed-off-by: Gokul K <gokul02k@gmail.com>
> ---
>  .../testing/selftests/kvm/include/sparsebit.h |  2 -
>  tools/testing/selftests/kvm/lib/sparsebit.c   | 63 +------------------
>  2 files changed, 1 insertion(+), 64 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/include/sparsebit.h b/tools/testing/selftests/kvm/include/sparsebit.h
> index e027e5790946..8a2ab11dae6f 100644
> --- a/tools/testing/selftests/kvm/include/sparsebit.h
> +++ b/tools/testing/selftests/kvm/include/sparsebit.h
> @@ -30,7 +30,6 @@ typedef u64 sparsebit_num_t;
>  
>  struct sparsebit *sparsebit_alloc(void);
>  void sparsebit_free(struct sparsebit **sbitp);
> -void sparsebit_copy(struct sparsebit *dstp, const struct sparsebit *src);

I'm somewhat tempted to keep sparsebit_copy() even though there are no users.
In the unlikely scenario someone wanted/needed to make a copy, it seems like a
potentially painful waste of time to have to recreate this or hunt down its prior
existence.

Anyone else have an opinion?

[PATCH 2/3] KVM: selftests: Delete the declaration of vcpu_set_cpuid_maxphyaddr()

[Gokul K]

vcpu_set_cpuid_maxphyaddr() is declared in include/x86/processor.h and
defined nowhere.  The declaration is the only mention of the name in
tools/testing/selftests, so nothing has ever been able to call it.

No Fixes: tag: a prototype for a function that does not exist cannot
have regressed anything, and there is nothing to backport.

No functional change intended.

Signed-off-by: Gokul K <gokul02k@gmail.com>
---
 tools/testing/selftests/kvm/include/x86/processor.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
index 7579e692bc2b..ffe95ce1ad49 100644
--- a/tools/testing/selftests/kvm/include/x86/processor.h
+++ b/tools/testing/selftests/kvm/include/x86/processor.h
@@ -1180,7 +1180,6 @@ static inline void vcpu_set_cpuid(struct kvm_vcpu *vcpu)
 void vcpu_set_cpuid_property(struct kvm_vcpu *vcpu,
 			     struct kvm_x86_cpu_property property,
 			     u32 value);
-void vcpu_set_cpuid_maxphyaddr(struct kvm_vcpu *vcpu, u8 maxphyaddr);
 
 void vcpu_clear_cpuid_entry(struct kvm_vcpu *vcpu, u32 function);
 
-- 
2.54.0

[PATCH 3/3] KVM: selftests: Delete the unused guest_snprintf()

[Gokul K]

guest_snprintf() is a varargs wrapper around guest_vsnprintf() that nothing
calls. Its declaration in test_util.h and its definition in
lib/guest_sprintf.c are the only two mentions anywhere under
tools/testing/selftests.

The rest of the family is alive: guest_vsnprintf() does the work and
ucall_common.c calls it, so this deletes the wrapper and nothing else.

No functional change intended.

Signed-off-by: Gokul K <gokul02k@gmail.com>
---
 tools/testing/selftests/kvm/include/test_util.h |  1 -
 tools/testing/selftests/kvm/lib/guest_sprintf.c | 12 ------------
 2 files changed, 13 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
index a6a3e1657895..fbdf0e0c15d1 100644
--- a/tools/testing/selftests/kvm/include/test_util.h
+++ b/tools/testing/selftests/kvm/include/test_util.h
@@ -238,7 +238,6 @@ static inline u32 atoi_non_negative(const char *name, const char *num_str)
 }
 
 int guest_vsnprintf(char *buf, int n, const char *fmt, va_list args);
-__printf(3, 4) int guest_snprintf(char *buf, int n, const char *fmt, ...);
 
 char *strdup_printf(const char *fmt, ...) __attribute__((format(printf, 1, 2), nonnull(1)));
 
diff --git a/tools/testing/selftests/kvm/lib/guest_sprintf.c b/tools/testing/selftests/kvm/lib/guest_sprintf.c
index 7a33965349a7..6caebb456f3d 100644
--- a/tools/testing/selftests/kvm/lib/guest_sprintf.c
+++ b/tools/testing/selftests/kvm/lib/guest_sprintf.c
@@ -300,15 +300,3 @@ int guest_vsnprintf(char *buf, int n, const char *fmt, va_list args)
 	*str = '\0';
 	return str - buf;
 }
-
-int guest_snprintf(char *buf, int n, const char *fmt, ...)
-{
-	va_list va;
-	int len;
-
-	va_start(va, fmt);
-	len = guest_vsnprintf(buf, n, fmt, va);
-	va_end(va);
-
-	return len;
-}
-- 
2.54.0

Re: [PATCH 3/3] KVM: selftests: Delete the unused guest_snprintf()

[Sean Christopherson]

On Fri, Sep 18, 2026, Gokul K wrote:
> guest_snprintf() is a varargs wrapper around guest_vsnprintf() that nothing
> calls. Its declaration in test_util.h and its definition in
> lib/guest_sprintf.c are the only two mentions anywhere under
> tools/testing/selftests.
> 
> The rest of the family is alive: guest_vsnprintf() does the work and
> ucall_common.c calls it, so this deletes the wrapper and nothing else.
> 
> No functional change intended.
> 
> Signed-off-by: Gokul K <gokul02k@gmail.com>
> ---
>  tools/testing/selftests/kvm/include/test_util.h |  1 -
>  tools/testing/selftests/kvm/lib/guest_sprintf.c | 12 ------------
>  2 files changed, 13 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
> index a6a3e1657895..fbdf0e0c15d1 100644
> --- a/tools/testing/selftests/kvm/include/test_util.h
> +++ b/tools/testing/selftests/kvm/include/test_util.h
> @@ -238,7 +238,6 @@ static inline u32 atoi_non_negative(const char *name, const char *num_str)
>  }
>  
>  int guest_vsnprintf(char *buf, int n, const char *fmt, va_list args);
> -__printf(3, 4) int guest_snprintf(char *buf, int n, const char *fmt, ...);
>  
>  char *strdup_printf(const char *fmt, ...) __attribute__((format(printf, 1, 2), nonnull(1)));
>  
> diff --git a/tools/testing/selftests/kvm/lib/guest_sprintf.c b/tools/testing/selftests/kvm/lib/guest_sprintf.c
> index 7a33965349a7..6caebb456f3d 100644
> --- a/tools/testing/selftests/kvm/lib/guest_sprintf.c
> +++ b/tools/testing/selftests/kvm/lib/guest_sprintf.c
> @@ -300,15 +300,3 @@ int guest_vsnprintf(char *buf, int n, const char *fmt, va_list args)
>  	*str = '\0';
>  	return str - buf;
>  }
> -
> -int guest_snprintf(char *buf, int n, const char *fmt, ...)
> -{
> -	va_list va;
> -	int len;
> -
> -	va_start(va, fmt);
> -	len = guest_vsnprintf(buf, n, fmt, va);
> -	va_end(va);
> -
> -	return len;
> -}

Hmm, I would rather turn guest_snprintf() into a macro so that it can be used in
variadic functions.  I can't think of any reason why this wouldn't work (and
emperically, guest printing works as expected).

---

From: Sean Christopherson <seanjc@google.com>
Date: Fri, 18 Sep 2026 08:57:37 -0700
Subject: [PATCH] KVM: selftests: Make guest_snprintf() a macro and use it as
 appropriate

Turn guest_snprintf() into a macro so that it can be used by variadic
functions, and use it in the ucall APIs instead of open coding the VA goo.

Reported-by: Gokul K <gokul02k@gmail.com>
Closes: https://lore.kernel.org/all/20260918113631.634233-4-gokul02k@gmail.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/include/test_util.h | 12 +++++++++++-
 tools/testing/selftests/kvm/lib/guest_sprintf.c | 12 ------------
 tools/testing/selftests/kvm/lib/ucall_common.c  | 10 ++--------
 3 files changed, 13 insertions(+), 21 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
index a6a3e1657895..817d4d5ca7cc 100644
--- a/tools/testing/selftests/kvm/include/test_util.h
+++ b/tools/testing/selftests/kvm/include/test_util.h
@@ -238,7 +238,17 @@ static inline u32 atoi_non_negative(const char *name, const char *num_str)
 }
 
 int guest_vsnprintf(char *buf, int n, const char *fmt, va_list args);
-__printf(3, 4) int guest_snprintf(char *buf, int n, const char *fmt, ...);
+
+#define guest_snprintf(__buf, __n, __fmt)		\
+({							\
+	va_list va;					\
+	int len;					\
+							\
+	va_start(va, __fmt);				\
+	len = guest_vsnprintf(__buf, __n, __fmt, va);	\
+	va_end(va);					\
+	len;						\
+})
 
 char *strdup_printf(const char *fmt, ...) __attribute__((format(printf, 1, 2), nonnull(1)));
 
diff --git a/tools/testing/selftests/kvm/lib/guest_sprintf.c b/tools/testing/selftests/kvm/lib/guest_sprintf.c
index 7a33965349a7..6caebb456f3d 100644
--- a/tools/testing/selftests/kvm/lib/guest_sprintf.c
+++ b/tools/testing/selftests/kvm/lib/guest_sprintf.c
@@ -300,15 +300,3 @@ int guest_vsnprintf(char *buf, int n, const char *fmt, va_list args)
 	*str = '\0';
 	return str - buf;
 }
-
-int guest_snprintf(char *buf, int n, const char *fmt, ...)
-{
-	va_list va;
-	int len;
-
-	va_start(va, fmt);
-	len = guest_vsnprintf(buf, n, fmt, va);
-	va_end(va);
-
-	return len;
-}
diff --git a/tools/testing/selftests/kvm/lib/ucall_common.c b/tools/testing/selftests/kvm/lib/ucall_common.c
index 029ce21f9f2f..e9df71197367 100644
--- a/tools/testing/selftests/kvm/lib/ucall_common.c
+++ b/tools/testing/selftests/kvm/lib/ucall_common.c
@@ -83,7 +83,6 @@ void ucall_assert(u64 cmd, const char *exp, const char *file,
 		  unsigned int line, const char *fmt, ...)
 {
 	struct ucall *uc;
-	va_list va;
 
 	uc = ucall_alloc();
 	uc->cmd = cmd;
@@ -92,9 +91,7 @@ void ucall_assert(u64 cmd, const char *exp, const char *file,
 	WRITE_ONCE(uc->args[GUEST_FILE], (u64)(file));
 	WRITE_ONCE(uc->args[GUEST_LINE], line);
 
-	va_start(va, fmt);
-	guest_vsnprintf(uc->buffer, UCALL_BUFFER_LEN, fmt, va);
-	va_end(va);
+	guest_snprintf(uc->buffer, UCALL_BUFFER_LEN, fmt);
 
 	ucall_arch_do_ucall((gva_t)uc->hva);
 
@@ -104,14 +101,11 @@ void ucall_assert(u64 cmd, const char *exp, const char *file,
 void ucall_fmt(u64 cmd, const char *fmt, ...)
 {
 	struct ucall *uc;
-	va_list va;
 
 	uc = ucall_alloc();
 	uc->cmd = cmd;
 
-	va_start(va, fmt);
-	guest_vsnprintf(uc->buffer, UCALL_BUFFER_LEN, fmt, va);
-	va_end(va);
+	guest_snprintf(uc->buffer, UCALL_BUFFER_LEN, fmt);
 
 	ucall_arch_do_ucall((gva_t)uc->hva);
 

base-commit: 70c944caf570fda2d79baa71435589a8db39f048
-- 

Re: [PATCH 0/3] KVM: selftests: Delete three pieces of dead library code

[Sean Christopherson]

On Fri, 18 Sep 2026 17:06:28 +0530, Gokul K wrote:
> Three unused things in the selftest library, found by asking the linker
> rather than by reading: build the selftests, then look for global symbols
> in lib/ that no object refers to, and check each survivor against the
> whole source tree by hand.
> 
>   1/3  sparsebit_copy() and sparsebit_num_set(), neither called
>   2/3  the declaration of vcpu_set_cpuid_maxphyaddr(), which has no
>        definition anywhere
>   3/3  guest_snprintf(), a varargs wrapper nobody calls
> 
> [...]

Applied 2 and 3 to kvm-x86 selftests, thanks!

[1/3] KVM: selftests: Delete the unused sparsebit copy and count helpers
      [SKIP, handled in a separate series]
[2/3] KVM: selftests: Delete the declaration of vcpu_set_cpuid_maxphyaddr()
      https://github.com/kvm-x86/linux/commit/dd572ec94640
[3/3] KVM: selftests: Delete the unused guest_snprintf()
      https://github.com/kvm-x86/linux/commit/3bac3b77c5e6

--
https://github.com/kvm-x86/linux/tree/next