Commit 6b878cbb authored by Reinette Chatre's avatar Reinette Chatre Committed by Sean Christopherson
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KVM: selftests: Add guest udelay() utility for x86 



Add udelay() for x86 tests to allow busy waiting in the guest for a
specific duration, and to match ARM and RISC-V's udelay() in the hopes
of eventually making udelay() available on all architectures.

Get the guest's TSC frequency using KVM_GET_TSC_KHZ and expose it to all
VMs via a new global, guest_tsc_khz.  Assert that KVM_GET_TSC_KHZ returns
a valid frequency, instead of simply skipping tests, which would require
detecting which tests actually need/want udelay().  KVM hasn't returned an
error for KVM_GET_TSC_KHZ since commit cc578287 ("KVM: Infrastructure
for software and hardware based TSC rate scaling"), which predates KVM
selftests by 6+ years (KVM_GET_TSC_KHZ itself predates KVM selftest by 7+
years).

Note, if the GUEST_ASSERT() in udelay() somehow fires and the test doesn't
check for guest asserts, then the test will fail with a very cryptic
message.  But fixing that, e.g. by automatically handling guest asserts,
is a much larger task, and practically speaking the odds of a test afoul
of this wart are infinitesimally small.

Signed-off-by: default avatarReinette Chatre <reinette.chatre@intel.com>
Link: https://lore.kernel.org/r/5aa86285d1c1d7fe1960e3fe490f4b22273977e6.1718214999.git.reinette.chatre@intel.com


Co-developed-by: default avatarSean Christopherson <seanjc@google.com>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent dd103407

tools/testing/selftests/kvm/include/x86_64/processor.h

+18 −0
Original line number Diff line number Diff line
@@ -23,6 +23,7 @@ 


extern bool host_cpu_is_intel;

extern bool host_cpu_is_amd;

extern uint64_t guest_tsc_khz;



/* Forced emulation prefix, used to invoke the emulator unconditionally. */

#define KVM_FEP "ud2; .byte 'k', 'v', 'm';"
@@ -815,6 +816,23 @@ 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(guest_tsc_khz);

	cycles = guest_tsc_khz / 1000 * usec;



	/*

	 * Deliberately don't PAUSE, a.k.a. cpu_relax(), so that the delay is

	 * as accurate as possible, e.g. doesn't trigger PAUSE-Loop VM-Exits.

	 */

	start = rdtsc();

	do {

		now = rdtsc();

	} while (now - start < cycles);

}



#define ud2()			\

	__asm__ __volatile__(	\

		"ud2\n"	\

tools/testing/selftests/kvm/lib/x86_64/processor.c

+11 −0
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ vm_vaddr_t exception_handlers; 
bool host_cpu_is_amd;

bool host_cpu_is_intel;

bool is_forced_emulation_enabled;

uint64_t guest_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.");

	guest_tsc_khz = r;

	sync_global_to_guest(vm, guest_tsc_khz);

}



void vcpu_arch_set_entry_point(struct kvm_vcpu *vcpu, void *guest_code)