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

Reinette Chatre
2024-06-12T18:16:22Z

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@intel.com>
---
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