Re: [kvm-unit-tests PATCH v9 21/31] powerpc: Add timebase tests

[Thomas Huth <thuth@redhat.com>]

On 04/05/2024 14.28, Nicholas Piggin wrote:
> This has a known failure on QEMU TCG machines where the decrementer
> interrupt is not lowered when the DEC wraps from -ve to +ve.

Would it then make sense to mark the test with accel = kvm to avoid the test 
failure when running with TCG?

> diff --git a/powerpc/timebase.c b/powerpc/timebase.c
> new file mode 100644
> index 000000000..02a4e33c0
> --- /dev/null
> +++ b/powerpc/timebase.c
> @@ -0,0 +1,331 @@
> +/* SPDX-License-Identifier: LGPL-2.0-only */
> +/*
> + * Test Timebase
> + *
> + * Copyright 2024 Nicholas Piggin, IBM Corp.
> + *
> + * This contains tests of timebase facility, TB, DEC, etc.
> + */
> +#include <libcflat.h>
> +#include <util.h>
> +#include <migrate.h>
> +#include <alloc.h>
> +#include <asm/handlers.h>
> +#include <devicetree.h>
> +#include <asm/hcall.h>
> +#include <asm/processor.h>
> +#include <asm/time.h>
> +#include <asm/barrier.h>
> +
> +static int dec_bits = 0;
> +
> +static void cpu_dec_bits(int fdtnode, u64 regval __unused, void *arg __unused)
> +{
> +	const struct fdt_property *prop;
> +	int plen;
> +
> +	prop = fdt_get_property(dt_fdt(), fdtnode, "ibm,dec-bits", &plen);
> +	if (!prop) {
> +		dec_bits = 32;
> +		return;
> +	}
> +
> +	/* Sanity check for the property layout (first two bytes are header) */
> +	assert(plen == 4);
> +
> +	dec_bits = fdt32_to_cpu(*(uint32_t *)prop->data);
> +}
> +
> +/* Check amount of CPUs nodes that have the TM flag */
> +static int find_dec_bits(void)
> +{
> +	int ret;
> +
> +	ret = dt_for_each_cpu_node(cpu_dec_bits, NULL);

What sense does it make to run this for each CPU node if the cpu_dec_bits 
function always overwrites the global dec_bits variable?
Wouldn't it be sufficient to run this for the first node only? Or should the 
cpu_dec_bits function maybe check that all nodes have the same value?

> +	if (ret < 0)
> +		return ret;
> +
> +	return dec_bits;
> +}
> +
> +
> +static bool do_migrate = false;
> +static volatile bool got_interrupt;
> +static volatile struct pt_regs recorded_regs;
> +
> +static uint64_t dec_max;
> +static uint64_t dec_min;
> +
> +static void test_tb(int argc, char **argv)
> +{
> +	uint64_t tb;
> +
> +	tb = get_tb();
> +	if (do_migrate)
> +		migrate();
> +	report(get_tb() >= tb, "timebase is incrementing");

If you use >= for testing, it could also mean that the TB stays at the same 
value, so "timebase is incrementing" sounds misleading. Maybe rather 
"timebase is not decreasing" ? Or wait a little bit, then check with ">" only ?

> +}
> +
> +static void dec_stop_handler(struct pt_regs *regs, void *data)
> +{
> +	mtspr(SPR_DEC, dec_max);
> +}
> +
> +static void dec_handler(struct pt_regs *regs, void *data)
> +{
> +	got_interrupt = true;
> +	memcpy((void *)&recorded_regs, regs, sizeof(struct pt_regs));
> +	regs->msr &= ~MSR_EE;
> +}
> +
> +static void test_dec(int argc, char **argv)
> +{
> +	uint64_t tb1, tb2, dec;
> +	int i;
> +
> +	handle_exception(0x900, &dec_handler, NULL);
> +
> +	for (i = 0; i < 100; i++) {
> +		tb1 = get_tb();
> +		mtspr(SPR_DEC, dec_max);
> +		dec = mfspr(SPR_DEC);
> +		tb2 = get_tb();
> +		if (tb2 - tb1 < dec_max - dec)
> +			break;
> +	}
> +	/* POWER CPUs can have a slight (few ticks) variation here */
> +	report_kfail(true, tb2 - tb1 >= dec_max - dec, "decrementer remains within TB after mtDEC");
> +
> +	tb1 = get_tb();
> +	mtspr(SPR_DEC, dec_max);
> +	mdelay(1000);
> +	dec = mfspr(SPR_DEC);
> +	tb2 = get_tb();
> +	report(tb2 - tb1 >= dec_max - dec, "decrementer remains within TB after 1s");
> +
> +	mtspr(SPR_DEC, dec_max);
> +	local_irq_enable();
> +	local_irq_disable();
> +	if (mfspr(SPR_DEC) <= dec_max) {
> +		report(!got_interrupt, "no interrupt on decrementer positive");
> +	}
> +	got_interrupt = false;
> +
> +	mtspr(SPR_DEC, 1);
> +	mdelay(100); /* Give the timer a chance to run */
> +	if (do_migrate)
> +		migrate();
> +	local_irq_enable();
> +	local_irq_disable();
> +	report(got_interrupt, "interrupt on decrementer underflow");
> +	got_interrupt = false;
> +
> +	if (do_migrate)
> +		migrate();
> +	local_irq_enable();
> +	local_irq_disable();
> +	report(got_interrupt, "interrupt on decrementer still underflown");
> +	got_interrupt = false;
> +
> +	mtspr(SPR_DEC, 0);
> +	mdelay(100); /* Give the timer a chance to run */
> +	if (do_migrate)
> +		migrate();
> +	local_irq_enable();
> +	local_irq_disable();
> +	report(got_interrupt, "DEC deal with set to 0");
> +	got_interrupt = false;
> +
> +	/* Test for level-triggered decrementer */
> +	mtspr(SPR_DEC, -1ULL);
> +	if (do_migrate)
> +		migrate();
> +	local_irq_enable();
> +	local_irq_disable();
> +	report(got_interrupt, "interrupt on decrementer write MSB");
> +	got_interrupt = false;
> +
> +	mtspr(SPR_DEC, dec_max);
> +	local_irq_enable();
> +	if (do_migrate)
> +		migrate();
> +	mtspr(SPR_DEC, -1);
> +	local_irq_disable();
> +	report(got_interrupt, "interrupt on decrementer write MSB with irqs on");
> +	got_interrupt = false;
> +
> +	mtspr(SPR_DEC, dec_min + 1);
> +	mdelay(100);
> +	local_irq_enable();
> +	local_irq_disable();
> +	/* TCG does not model this correctly */
> +	report_kfail(true, !got_interrupt, "no interrupt after wrap to positive");
> +	got_interrupt = false;
> +
> +	handle_exception(0x900, NULL, NULL);
> +}
> +
> +static void test_hdec(int argc, char **argv)
> +{
> +	uint64_t tb1, tb2, hdec;
> +
> +	if (!machine_is_powernv()) {
> +		report_skip("skipping on !powernv machine");

I'd rather say "not running on powernv machine"

> +		return;
> +	}

  Thomas