Re: [kvm-unit-tests PATCH v10 4/7] arm/tlbflush-code: TLB flush during code execution

[Andrew Jones]

On Tue, Mar 07, 2023 at 11:28:42AM +0000, Alex Bennée wrote:
> This adds a fairly brain dead torture test for TLB flushes intended
> for stressing the MTTCG QEMU build. It takes the usual -smp option for
> multiple CPUs.
> 
> By default it CPU0 will do a TLBIALL flush after each cycle. You can
> pass options via -append to control additional aspects of the test:
> 
>   - "page" flush each page in turn (one per function)
>   - "self" do the flush after each computation cycle
>   - "verbose" report progress on each computation cycle
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> CC: Mark Rutland <mark.rutland@arm.com>
> Message-Id: <20211118184650.661575-7-alex.bennee@linaro.org>
> 
> ---
> v9
>   - move tests back into unittests.cfg (with nodefault mttcg)
>   - replace printf with report_info
>   - drop accel = tcg
> ---
>  arm/Makefile.common |   1 +
>  arm/tlbflush-code.c | 209 ++++++++++++++++++++++++++++++++++++++++++++
>  arm/unittests.cfg   |  25 ++++++
>  3 files changed, 235 insertions(+)
>  create mode 100644 arm/tlbflush-code.c
> 
> diff --git a/arm/Makefile.common b/arm/Makefile.common
> index 16f8c6df..2c4aad38 100644
> --- a/arm/Makefile.common
> +++ b/arm/Makefile.common
> @@ -12,6 +12,7 @@ tests-common += $(TEST_DIR)/gic.flat
>  tests-common += $(TEST_DIR)/psci.flat
>  tests-common += $(TEST_DIR)/sieve.flat
>  tests-common += $(TEST_DIR)/pl031.flat
> +tests-common += $(TEST_DIR)/tlbflush-code.flat
>  
>  tests-all = $(tests-common) $(tests)
>  all: directories $(tests-all)
> diff --git a/arm/tlbflush-code.c b/arm/tlbflush-code.c
> new file mode 100644
> index 00000000..bf9eb111
> --- /dev/null
> +++ b/arm/tlbflush-code.c
> @@ -0,0 +1,209 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * TLB Flush Race Tests
> + *
> + * These tests are designed to test for incorrect TLB flush semantics
> + * under emulation. The initial CPU will set all the others working a
> + * compuation task and will then trigger TLB flushes across the

computation

> + * system. It doesn't actually need to re-map anything but the flushes
> + * themselves will trigger QEMU's TCG self-modifying code detection
> + * which will invalidate any generated  code causing re-translation.
> + * Eventually the code buffer will fill and a general tb_lush() will
> + * be triggered.
> + *
> + * Copyright (C) 2016-2021, Linaro, Alex Bennée <alex.bennee@linaro.org>
> + *
> + * This work is licensed under the terms of the GNU LGPL, version 2.
> + */
> +
> +#include <libcflat.h>
> +#include <asm/smp.h>
> +#include <asm/cpumask.h>
> +#include <asm/barrier.h>
> +#include <asm/mmu.h>
> +
> +#define SEQ_LENGTH 10
> +#define SEQ_HASH 0x7cd707fe
> +
> +static cpumask_t smp_test_complete;
> +static int flush_count = 1000000;
> +static bool flush_self;
> +static bool flush_page;
> +static bool flush_verbose;
> +
> +/*
> + * Work functions
> + *
> + * These work functions need to be:
> + *
> + *  - page aligned, so we can flush one function at a time
> + *  - have branches, so QEMU TCG generates multiple basic blocks
> + *  - call across pages, so we exercise the TCG basic block slow path
> + */
> +
> +/* Adler32 */
> +__attribute__((aligned(PAGE_SIZE))) static
> +uint32_t hash_array(const void *buf, size_t buflen)
> +{
> +     const uint8_t *data = (uint8_t *) buf;
> +     uint32_t s1 = 1;
> +     uint32_t s2 = 0;
> +
> +     for (size_t n = 0; n < buflen; n++) {
> +             s1 = (s1 + data[n]) % 65521;
> +             s2 = (s2 + s1) % 65521;
> +     }
> +     return (s2 << 16) | s1;
> +}
> +
> +__attribute__((aligned(PAGE_SIZE))) static
> +void create_fib_sequence(int length, unsigned int *array)
> +{
> +     int i;
> +
> +     /* first two values */
> +     array[0] = 0;
> +     array[1] = 1;
> +     for (i = 2; i < length; i++)
> +             array[i] = array[i-2] + array[i-1];
> +}
> +
> +__attribute__((aligned(PAGE_SIZE))) static
> +unsigned long long factorial(unsigned int n)
> +{
> +     unsigned int i;
> +     unsigned long long fac = 1;
> +
> +     for (i = 1; i <= n; i++)
> +             fac = fac * i;
> +     return fac;
> +}
> +
> +__attribute__((aligned(PAGE_SIZE))) static
> +void factorial_array(unsigned int n, unsigned int *input,
> +                  unsigned long long *output)
> +{
> +     unsigned int i;
> +
> +     for (i = 0; i < n; i++)
> +             output[i] = factorial(input[i]);
> +}
> +
> +__attribute__((aligned(PAGE_SIZE))) static
> +unsigned int do_computation(void)
> +{
> +     unsigned int fib_array[SEQ_LENGTH];
> +     unsigned long long facfib_array[SEQ_LENGTH];
> +     uint32_t fib_hash, facfib_hash;
> +
> +     create_fib_sequence(SEQ_LENGTH, &fib_array[0]);
> +     fib_hash = hash_array(&fib_array[0], sizeof(fib_array));
> +     factorial_array(SEQ_LENGTH, &fib_array[0], &facfib_array[0]);
> +     facfib_hash = hash_array(&facfib_array[0], sizeof(facfib_array));
> +
> +     return (fib_hash ^ facfib_hash);
> +}
> +
> +/* This provides a table of the work functions so we can flush each
> + * page individually
> + */
> +static void *pages[] = {&hash_array, &create_fib_sequence, &factorial,
> +                     &factorial_array, &do_computation};
> +
> +static void do_flush(int i)
> +{
> +     if (flush_page)
> +             flush_tlb_page((unsigned long)pages[i % ARRAY_SIZE(pages)]);
> +     else
> +             flush_tlb_all();
> +}
> +
> +
> +static void just_compute(void)
> +{
> +     int i, errors = 0;
> +     int cpu = smp_processor_id();
> +
> +     uint32_t result;
> +
> +     report_info("CPU%d online", cpu);
> +
> +     for (i = 0 ; i < flush_count; i++) {
> +             result = do_computation();
> +
> +             if (result != SEQ_HASH) {
> +                     errors++;
> +                     report_info("CPU%d: seq%d 0x%"PRIx32"!=0x%x",
> +                                 cpu, i, result, SEQ_HASH);
> +             }
> +
> +             if (flush_verbose && (i % 1000) == 0)
> +                     report_info("CPU%d: seq%d", cpu, i);
> +
> +             if (flush_self)
> +                     do_flush(i);
> +     }
> +
> +     report(errors == 0, "CPU%d: Done - Errors: %d", cpu, errors);
> +
> +     cpumask_set_cpu(cpu, &smp_test_complete);
> +     if (cpu != 0)
> +             halt();
> +}
> +
> +static void just_flush(void)
> +{
> +     int cpu = smp_processor_id();
> +     int i = 0;
> +
> +     /*
> +      * Set our CPU as done, keep flushing until everyone else
> +      * finished
> +      */
> +     cpumask_set_cpu(cpu, &smp_test_complete);
> +
> +     while (!cpumask_full(&smp_test_complete))
> +             do_flush(i++);
> +
> +     report_info("CPU%d: Done - Triggered %d flushes", cpu, i);
> +}
> +
> +int main(int argc, char **argv)
> +{
> +     int cpu, i;
> +     char prefix[100];
> +
> +     for (i = 0; i < argc; i++) {
> +             char *arg = argv[i];
> +
> +             if (strcmp(arg, "page") == 0)
> +                     flush_page = true;
> +
> +             if (strcmp(arg, "self") == 0)
> +                     flush_self = true;
> +
> +             if (strcmp(arg, "verbose") == 0)
> +                     flush_verbose = true;
> +     }
> +
> +     snprintf(prefix, sizeof(prefix), "tlbflush_%s_%s",
> +              flush_page ? "page" : "all",
> +              flush_self ? "self" : "other");
> +     report_prefix_push(prefix);
> +
> +     for_each_present_cpu(cpu) {
> +             if (cpu == 0)
> +                     continue;
> +             smp_boot_secondary(cpu, just_compute);
> +     }
> +
> +     if (flush_self)
> +             just_compute();
> +     else
> +             just_flush();
> +
> +     while (!cpumask_full(&smp_test_complete))
> +             cpu_relax();
> +
> +     return report_summary();
> +}
> diff --git a/arm/unittests.cfg b/arm/unittests.cfg
> index 5e67b558..ee21aef4 100644
> --- a/arm/unittests.cfg
> +++ b/arm/unittests.cfg
> @@ -275,3 +275,28 @@ file = debug.flat
>  arch = arm64
>  extra_params = -append 'ss-migration'
>  groups = debug migration
> +
> +# TLB Torture Tests
> +[tlbflush-code::all_other]

It's better to use '-', '_', '.', or ',' than '::' because otherwise the
standalone test will have a filename like tests/tlbflush-code::all_other
which will be awkward for shells.

BTW, have you tried running these tests as standalone? Since they're
'nodefault' it'd be good if they work that way.

> +file = tlbflush-code.flat
> +smp = $(($MAX_SMP>4?4:$MAX_SMP))
> +groups = nodefault mttcg
> +
> +[tlbflush-code::page_other]
> +file = tlbflush-code.flat
> +smp = $(($MAX_SMP>4?4:$MAX_SMP))
> +extra_params = -append 'page'
> +groups = nodefault mttcg
> +
> +[tlbflush-code::all_self]
> +file = tlbflush-code.flat
> +smp = $(($MAX_SMP>4?4:$MAX_SMP))
> +extra_params = -append 'self'
> +groups = nodefault mttcg
> +
> +[tlbflush-code::page_self]
> +file = tlbflush-code.flat
> +smp = $(($MAX_SMP>4?4:$MAX_SMP))
> +extra_params = -append 'page self'
> +groups = nodefault mttcg
> +
> -- 
> 2.39.2
>

Thanks,
drew