[PATCH V9 1/2] KVM: selftests: Add x86_64 guest udelay() utility

[Reinette Chatre]

Create udelay() utility for x86_64 tests to match
udelay() available to ARM and RISC-V tests.

Calibrate guest frequency using the KVM_GET_TSC_KHZ ioctl()
and share it between host and guest with the new
tsc_khz global variable.

Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
---
Changes v9:
- Change tsc_kz type to uint32_t (was unsigned int). (Sean)
- Change type used to store number of cycles to uint64_t
  (was unsigned long). (Sean)
- Add GUEST_ASSERT() in udelay() used in guest to avoid risk of
  udelay() unexpectedly doing nothing if something went wrong
  during TSC frequency discovery. (Sean)
- Use TEST_ASSERT() when checking for KVM_CAP_GET_TSC_KHZ. (Sean)
- Use TEST_ASSERT() to enforce that discovery of TSC frequency
  must never fail. (Sean)

Changes v8:
- Use appropriate signed type to discover TSC freq from KVM.
- Switch type used to store TSC frequency from unsigned long
  to unsigned int to match the type used by the kernel.

Changes v7:
- New patch
---
 .../selftests/kvm/include/x86_64/processor.h    | 17 +++++++++++++++++
 .../selftests/kvm/lib/x86_64/processor.c        | 11 +++++++++++
 2 files changed, 28 insertions(+)

diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
index c0c7c1fe93f9..383a0f7fa9ef 100644
--- a/tools/testing/selftests/kvm/include/x86_64/processor.h
+++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
@@ -23,6 +23,7 @@
 
 extern bool host_cpu_is_intel;
 extern bool host_cpu_is_amd;
+extern uint32_t tsc_khz;
 
 /* Forced emulation prefix, used to invoke the emulator unconditionally. */
 #define KVM_FEP "ud2; .byte 'k', 'v', 'm';"
@@ -816,6 +817,22 @@ static inline void cpu_relax(void)
 	asm volatile("rep; nop" ::: "memory");
 }
 
+static inline void udelay(unsigned long usec)
+{
+	uint64_t start, now, cycles;
+
+	GUEST_ASSERT(tsc_khz);
+	cycles = tsc_khz / 1000 * usec;
+
+	start = rdtsc();
+	for (;;) {
+		now = rdtsc();
+		if (now - start >= cycles)
+			break;
+		cpu_relax();
+	}
+}
+
 #define ud2()			\
 	__asm__ __volatile__(	\
 		"ud2\n"	\
diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
index 594b061aef52..aaadda1ebcad 100644
--- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
@@ -25,6 +25,7 @@ vm_vaddr_t exception_handlers;
 bool host_cpu_is_amd;
 bool host_cpu_is_intel;
 bool is_forced_emulation_enabled;
+uint32_t tsc_khz;
 
 static void regs_dump(FILE *stream, struct kvm_regs *regs, uint8_t indent)
 {
@@ -616,6 +617,11 @@ void assert_on_unhandled_exception(struct kvm_vcpu *vcpu)
 
 void kvm_arch_vm_post_create(struct kvm_vm *vm)
 {
+	int r;
+
+	TEST_ASSERT(kvm_has_cap(KVM_CAP_GET_TSC_KHZ),
+		    "Require KVM_GET_TSC_KHZ to provide udelay() to guest.");
+
 	vm_create_irqchip(vm);
 	vm_init_descriptor_tables(vm);
 
@@ -628,6 +634,11 @@ void kvm_arch_vm_post_create(struct kvm_vm *vm)
 
 		vm_sev_ioctl(vm, KVM_SEV_INIT2, &init);
 	}
+
+	r = __vm_ioctl(vm, KVM_GET_TSC_KHZ, NULL);
+	TEST_ASSERT(r > 0, "KVM_GET_TSC_KHZ did not provide a valid TSC frequency.");
+	tsc_khz = r;
+	sync_global_to_guest(vm, tsc_khz);
 }
 
 void vcpu_arch_set_entry_point(struct kvm_vcpu *vcpu, void *guest_code)
-- 
2.34.1