Re: [PATCH v2 3/3] KVM: selftests: Add test case for x86 apic_bus_clock_frequency

[Maxim Levitsky <mlevitsk@redhat.com>]

On Mon, 2023-11-13 at 20:35 -0800, isaku.yamahata@intel.com wrote:
> From: Isaku Yamahata <isaku.yamahata@intel.com>
> 
> Test if the apic bus clock frequency is exptected to the configured value.
> Set APIC TMICT to the maximum value and busy wait for 100 msec (any value
> is okay) with tsc value, and read TMCCT. Calculate apic bus clock frequency
> based on TSC frequency.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> ---
> Changes v2:
> - Newly added
> ---
>  tools/testing/selftests/kvm/Makefile          |   1 +
>  .../selftests/kvm/include/x86_64/apic.h       |   7 +
>  .../kvm/x86_64/apic_bus_clock_test.c          | 132 ++++++++++++++++++
>  3 files changed, 140 insertions(+)
>  create mode 100644 tools/testing/selftests/kvm/x86_64/apic_bus_clock_test.c
> 
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index a5963ab9215b..74ed3f71b6e8 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -115,6 +115,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/vmx_invalid_nested_guest_state
>  TEST_GEN_PROGS_x86_64 += x86_64/vmx_set_nested_state_test
>  TEST_GEN_PROGS_x86_64 += x86_64/vmx_tsc_adjust_test
>  TEST_GEN_PROGS_x86_64 += x86_64/vmx_nested_tsc_scaling_test
> +TEST_GEN_PROGS_x86_64 += x86_64/apic_bus_clock_test
>  TEST_GEN_PROGS_x86_64 += x86_64/xapic_ipi_test
>  TEST_GEN_PROGS_x86_64 += x86_64/xapic_state_test
>  TEST_GEN_PROGS_x86_64 += x86_64/xcr0_cpuid_test
> diff --git a/tools/testing/selftests/kvm/include/x86_64/apic.h b/tools/testing/selftests/kvm/include/x86_64/apic.h
> index bed316fdecd5..866a58d5fa11 100644
> --- a/tools/testing/selftests/kvm/include/x86_64/apic.h
> +++ b/tools/testing/selftests/kvm/include/x86_64/apic.h
> @@ -60,6 +60,13 @@
>  #define		APIC_VECTOR_MASK	0x000FF
>  #define	APIC_ICR2	0x310
>  #define		SET_APIC_DEST_FIELD(x)	((x) << 24)
> +#define APIC_LVT0       0x350
> +#define         APIC_LVT_TIMER_ONESHOT          (0 << 17)
> +#define         APIC_LVT_TIMER_PERIODIC         (1 << 17)
> +#define         APIC_LVT_TIMER_TSCDEADLINE      (2 << 17)
> +#define APIC_TMICT	0x380
> +#define APIC_TMCCT	0x390
> +#define APIC_TDCR	0x3E0
>  
>  void apic_disable(void);
>  void xapic_enable(void);
> diff --git a/tools/testing/selftests/kvm/x86_64/apic_bus_clock_test.c b/tools/testing/selftests/kvm/x86_64/apic_bus_clock_test.c
> new file mode 100644
> index 000000000000..91f558d7c624
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/x86_64/apic_bus_clock_test.c
> @@ -0,0 +1,132 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#define _GNU_SOURCE /* for program_invocation_short_name */
> +
> +#include "apic.h"
> +#include "test_util.h"
> +
> +/* Pick one convenient value, 1Ghz.  No special meaning. */
Tiny nitpick: to be 100% honest, 1Ghz does have a special meaning, it's the default APIC bus frequency.
It might be slightly better to use say 1.5Ghz or something like that.

> +#define TSC_HZ			(1 * 1000 * 1000 * 1000ULL)
> +
> +/* Wait for 100 msec, not too long, not too short value. */
> +#define LOOP_MSEC		100ULL
> +#define TSC_WAIT_DELTA		(TSC_HZ / 1000 * LOOP_MSEC)
> +
> +/* Pick up typical value.  Different enough from the default value, 1GHz.  */
> +#define APIC_BUS_CLOCK_FREQ	(25 * 1000 * 1000ULL)
> +
> +static void guest_code(void)
> +{
> +	/* Possible tdcr values and its divide count. */
> +	struct {
> +		u32 tdcr;
> +		u32 divide_count;
> +	} tdcrs[] = {
> +		{0x0, 2},
> +		{0x1, 4},
> +		{0x2, 8},
> +		{0x3, 16},
> +		{0x8, 32},
> +		{0x9, 64},
> +		{0xa, 128},
> +		{0xb, 1},
> +	};
> +
> +	u32 tmict, tmcct;
> +	u64 tsc0, tsc1;
> +	int i;
> +
> +	asm volatile("cli");
> +
> +	xapic_enable();
> +
> +	/*
> +	 * Setup one-shot timer.  Because we don't fire the interrupt, the
> +	 * vector doesn't matter.
> +	 */
> +	xapic_write_reg(APIC_LVT0, APIC_LVT_TIMER_ONESHOT);
> +
> +	for (i = 0; i < ARRAY_SIZE(tdcrs); i++) {
> +		xapic_write_reg(APIC_TDCR, tdcrs[i].tdcr);
> +
> +		/* Set the largest value to not trigger the interrupt. */
> +		tmict = ~0;
> +		xapic_write_reg(APIC_TMICT, tmict);
> +
> +		/* Busy wait for LOOP_MSEC */
> +		tsc0 = rdtsc();
> +		tsc1 = tsc0;
> +		while (tsc1 - tsc0 < TSC_WAIT_DELTA)
> +			tsc1 = rdtsc();
> +
> +		/* Read apic timer and tsc */
> +		tmcct = xapic_read_reg(APIC_TMCCT);
> +		tsc1 = rdtsc();
> +
> +		/* Stop timer */
> +		xapic_write_reg(APIC_TMICT, 0);
> +
> +		/* Report it. */
> +		GUEST_SYNC_ARGS(tdcrs[i].divide_count, tmict - tmcct,
> +				tsc1 - tsc0, 0, 0);
> +	}
> +
> +	GUEST_DONE();
> +}
> +
> +void test_apic_bus_clock(struct kvm_vcpu *vcpu)
> +{
> +	bool done = false;
> +	struct ucall uc;
> +
> +	while (!done) {
> +		vcpu_run(vcpu);
> +		TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
> +
> +		switch (get_ucall(vcpu, &uc)) {
> +		case UCALL_DONE:
> +			done = true;
> +			break;
> +		case UCALL_ABORT:
> +			REPORT_GUEST_ASSERT(uc);
> +			break;
> +		case UCALL_SYNC: {
> +			u32 divide_counter = uc.args[1];
> +			u32 apic_cycles = uc.args[2];
> +			u64 tsc_cycles = uc.args[3];
> +			u64 freq;
> +
> +			TEST_ASSERT(tsc_cycles > 0,
> +				    "tsc cycles must not be zero.");
> +
> +			/* Allow 1% slack. */
> +			freq = apic_cycles * divide_counter * TSC_HZ / tsc_cycles;
> +			TEST_ASSERT(freq < APIC_BUS_CLOCK_FREQ * 101 / 100,
> +				    "APIC bus clock frequency is too large");
> +			TEST_ASSERT(freq > APIC_BUS_CLOCK_FREQ * 99 / 100,
> +				    "APIC bus clock frequency is too small");
> +			break;
> +		}
> +		default:
> +			TEST_FAIL("Unknown ucall %lu", uc.cmd);
> +			break;
> +		}
> +	}
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	struct kvm_vm *vm;
> +	struct kvm_vcpu *vcpu;
> +
> +	vm = __vm_create(VM_MODE_DEFAULT, 1, 0);
> +	vm_ioctl(vm, KVM_SET_TSC_KHZ, (void *) (TSC_HZ / 1000));
> +	/*  KVM_CAP_X86_BUS_FREQUENCY_CONTROL requires that no vcpu is created. */
> +	vm_enable_cap(vm, KVM_CAP_X86_BUS_FREQUENCY_CONTROL,
> +		      APIC_BUS_CLOCK_FREQ);
> +	vcpu = vm_vcpu_add(vm, 0, guest_code);
> +
> +	virt_pg_map(vm, APIC_DEFAULT_GPA, APIC_DEFAULT_GPA);
> +
> +	test_apic_bus_clock(vcpu);
> +	kvm_vm_free(vm);
> +}

Looks good overall.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
	Maxim Levitsky