[PATCH v2] KVM: selftests: hyperv_tlb_flush: replace NOP loop with udelay()

Piotr Zarycki
2026-04-22T13:03:45Z

Replace the open-coded NOP loop with udelay() which was added to KVM
selftests in commit 6b878cbb87bf ("KVM: selftests: Add guest udelay()
utility for x86"). The NOP loop is CPU speed dependent while udelay()
provides a deterministic delay regardless of host CPU frequency.

Signed-off-by: Piotr Zarycki <piotr.zarycki@gmail.com>
---
.../testing/selftests/kvm/x86/hyperv_tlb_flush.c | 15 ++-------------
1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86/hyperv_tlb_flush.c b/tools/testing/selftests/kvm/x86/hyperv_tlb_flush.c
index c542cc4762b1..4b7f089542c1 100644
--- a/tools/testing/selftests/kvm/x86/hyperv_tlb_flush.c
+++ b/tools/testing/selftests/kvm/x86/hyperv_tlb_flush.c
@@ -141,17 +141,6 @@ static void swap_two_test_pages(vm_paddr_t pte_gva1, vm_paddr_t pte_gva2)
*(uint64_t *)pte_gva2 = tmp;
}

-/*
- * TODO: replace the silly NOP loop with a proper udelay() implementation.
- */
-static inline void do_delay(void)
-{
- int i;
-
- for (i = 0; i < 1000000; i++)
- asm volatile("nop");
-}
-
/*
* Prepare to test: 'disable' workers by setting the expectation to '0',
* clear hypercall input page and then swap two test pages.
@@ -169,7 +158,7 @@ static inline void prepare_to_test(struct test_data *data)
wmb();

/* Make sure workers have enough time to notice */
- do_delay();
+ udelay(100);

/* Swap test page mappings */
swap_two_test_pages(data->test_pages_pte[0], data->test_pages_pte[1]);
@@ -189,7 +178,7 @@ static inline void post_test(struct test_data *data, u64 exp1, u64 exp2)
set_expected_val((void *)data->test_pages, exp2, WORKER_VCPU_ID_2);

/* Make sure workers have enough time to test */
- do_delay();
+ udelay(100);
}

#define TESTVAL1 0x0101010101010101
--
2.53.0