Re: [kvm-unit-tests PATCH v5 1/2] s390x: Add specification exception test

[Janosch Frank]

On 7/20/22 16:25, Janis Schoetterl-Glausch wrote:
> Generate specification exceptions and check that they occur.
>
> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
> ---
>   s390x/Makefile           |   1 +
>   lib/s390x/asm/arch_def.h |   5 ++
>   s390x/spec_ex.c          | 180 +++++++++++++++++++++++++++++++++++++++
>   s390x/unittests.cfg      |   3 +
>   4 files changed, 189 insertions(+)
>   create mode 100644 s390x/spec_ex.c
>
> diff --git a/s390x/Makefile b/s390x/Makefile
> index efd5e0c1..58b1bf54 100644
> --- a/s390x/Makefile
> +++ b/s390x/Makefile
> @@ -27,6 +27,7 @@ tests += $(TEST_DIR)/uv-host.elf
>   tests += $(TEST_DIR)/edat.elf
>   tests += $(TEST_DIR)/mvpg-sie.elf
>   tests += $(TEST_DIR)/spec_ex-sie.elf
> +tests += $(TEST_DIR)/spec_ex.elf
>   tests += $(TEST_DIR)/firq.elf
>   tests += $(TEST_DIR)/epsw.elf
>   tests += $(TEST_DIR)/adtl-status.elf
> diff --git a/lib/s390x/asm/arch_def.h b/lib/s390x/asm/arch_def.h
> index 78b257b7..8fbc451c 100644
> --- a/lib/s390x/asm/arch_def.h
> +++ b/lib/s390x/asm/arch_def.h
> @@ -41,6 +41,11 @@ struct psw {
>         uint64_t        addr;
>   };
>   
> +struct short_psw {
> +       uint32_t        mask;
> +       uint32_t        addr;
> +};
> +
>   #define AS_PRIM                               0
>   #define AS_ACCR                               1
>   #define AS_SECN                               2
> diff --git a/s390x/spec_ex.c b/s390x/spec_ex.c
> new file mode 100644
> index 00000000..77fc6246
> --- /dev/null
> +++ b/s390x/spec_ex.c
> @@ -0,0 +1,180 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright IBM Corp. 2021, 2022
> + *
> + * Specification exception test.
> + * Tests that specification exceptions occur when expected.
> + *
> + * Can be extended by adding triggers to spec_ex_triggers, see comments below.
> + */
> +#include <stdlib.h>

Which things are you hoping to include from stdlib.h?
As we normally use libcflat including external files can be pretty 
dangerous.

> +#include <libcflat.h>
> +#include <asm/interrupt.h>
> +
> +static bool invalid_psw_expected;
> +static struct psw expected_psw;
> +static struct psw invalid_psw;
> +static struct psw fixup_psw;
> +
> +/*
> + * The standard program exception handler cannot deal with invalid old PSWs,
> + * especially not invalid instruction addresses, as in that case one cannot
> + * find the instruction following the faulting one from the old PSW.
> + * The PSW to return to is set by load_psw.
> + */
> +static void fixup_invalid_psw(void)
> +{
> +       /* signal occurrence of invalid psw fixup */
> +       invalid_psw_expected = false;
> +       invalid_psw = lowcore.pgm_old_psw;
> +       lowcore.pgm_old_psw = fixup_psw;
> +}
> +
> +/*
> + * Load possibly invalid psw, but setup fixup_psw before,
> + * so that fixup_invalid_psw() can bring us back onto the right track.
> + * Also acts as compiler barrier, -> none required in expect/check_invalid_psw
> + */
> +static void load_psw(struct psw psw)
> +{
> +       uint64_t scratch;
> +

/*
Store a valid mask and the address of the nop into the fixup PSW.
Then load the possibly invalid PSW.
*/

> +       fixup_psw.mask = extract_psw_mask();
> +       asm volatile ( "larl       %[scratch],0f\n"
> +               "  stg     %[scratch],%[addr]\n"
> +               "  lpswe   %[psw]\n"
> +               "0:        nop\n"
> +               : [scratch] "=&d"(scratch),
> +                 [addr] "=&T"(fixup_psw.addr)

s/addr/psw_addr/ ?

> +               : [psw] "Q"(psw)
> +               : "cc", "memory"
> +       );
> +}
> +
> +static void load_short_psw(struct short_psw psw)
> +{
> +       uint64_t scratch;
> +
> +       fixup_psw.mask = extract_psw_mask();
> +       asm volatile ( "larl       %[scratch],0f\n"
> +               "  stg     %[scratch],%[addr]\n"
> +               "  lpsw    %[psw]\n"
> +               "0:        nop\n"
> +               : [scratch] "=&d"(scratch),
> +                 [addr] "=&T"(fixup_psw.addr)
> +               : [psw] "Q"(psw)
> +               : "cc", "memory"
> +       );

Same story.

> +}
> +
> +static void expect_invalid_psw(struct psw psw)
> +{
> +       expected_psw = psw;
> +       invalid_psw_expected = true;
> +}
> +
> +static int check_invalid_psw(void)
> +{
> +       /* toggled to signal occurrence of invalid psw fixup */

That comment's location is a bit weird.
Move it to the declaration of the variable.

> +       if (!invalid_psw_expected) {
> +               if (expected_psw.mask == invalid_psw.mask &&
> +                   expected_psw.addr == invalid_psw.addr)
> +                       return 0;
> +               report_fail("Wrong invalid PSW");
> +       } else {
> +               report_fail("Expected exception due to invalid PSW");
> +       }
> +       return 1;
> +}
> +

/* For normal PSWs bit 12 has to be 0 to be a valid PSW*/

> +static int psw_bit_12_is_1(void)
> +{
> +       struct psw invalid = { .mask = 0x0008000000000000, .addr = 
> 0x00000000deadbeee};

You could use BIT(63-12) for the mask.
I usually but struct initializations on new lines, it's easier to read.

> +
> +       expect_invalid_psw(invalid);
> +       load_psw(invalid);
> +       return check_invalid_psw();
> +}
> +

/* A short PSW needs to have bit 12 set to be valid. */
> +static int short_psw_bit_12_is_0(void)
> +{
> +       struct short_psw short_invalid = { .mask = 0x00000000, .addr = 
> 0xdeadbeee};

I don't see a reason to specify more than one 0 if the whole value is 0.

> +
> +       /*
> +        * lpsw may optionally check bit 12 before loading the new psw
> +        * -> cannot check the expected invalid psw like with lpswe
> +        */
> +       load_short_psw(short_invalid);
> +       return 0;
> +}
> +
> +static int bad_alignment(void)
> +{
> +       uint32_t words[5] __attribute__((aligned(16)));
> +       uint32_t (*bad_aligned)[4] = (uint32_t (*)[4])&words[1];
> +

/* lpq loads a quad word into a register pair and requires quad word 
alignment */

> +       asm volatile ("lpq %%r6,%[bad]"

Of course there's an instruction for that...

> +                     : : [bad] "T"(*bad_aligned)
> +                     : "%r6", "%r7"
> +       );
> +       return 0;
> +}
> +
> +static int not_even(void)
> +{
> +       uint64_t quad[2] __attribute__((aligned(16))) = {0};
> +
> +       asm volatile (".insn       rxy,0xe3000000008f,%%r7,%[quad]" /* lpq 
> %%r7,%[quad] */
> +                     : : [quad] "T"(quad)

Is there a reason you never put a space after the constraint?

> +                     : "%r7", "%r8"
> +       );
> +       return 0;
> +}
> +
> +/*
> + * Harness for specification exception testing.
> + * func only triggers exception, reporting is taken care of automatically.
> + */
> +struct spec_ex_trigger {
> +       const char *name;
> +       int (*func)(void);
> +       void (*fixup)(void);
> +};
> +
> +/* List of all tests to execute */
> +static const struct spec_ex_trigger spec_ex_triggers[] = {
> +       { "psw_bit_12_is_1", &psw_bit_12_is_1, &fixup_invalid_psw },
> +       { "short_psw_bit_12_is_0", &short_psw_bit_12_is_0, &fixup_invalid_psw },
> +       { "bad_alignment", &bad_alignment, NULL },
> +       { "not_even", &not_even, NULL },
> +       { NULL, NULL, NULL },
> +};
> +
> +static void test_spec_ex(const struct spec_ex_trigger *trigger)
> +{
> +       int rc;
> +
> +       expect_pgm_int();
> +       register_pgm_cleanup_func(trigger->fixup);
> +       rc = trigger->func();
> +       register_pgm_cleanup_func(NULL);
> +       /* test failed, nothing to be done, reporting responsibility of trigger 
> */
> +       if (rc)
> +               return;
> +       check_pgm_int_code(PGM_INT_CODE_SPECIFICATION);
> +}
> +
> +int main(int argc, char **argv)
> +{
> +       unsigned int i;
> +
> +       report_prefix_push("specification exception");
> +       for (i = 0; spec_ex_triggers[i].name; i++) {
> +               report_prefix_push(spec_ex_triggers[i].name);
> +               test_spec_ex(&spec_ex_triggers[i]);
> +               report_prefix_pop();
> +       }
> +       report_prefix_pop();
> +
> +       return report_summary();
> +}
> diff --git a/s390x/unittests.cfg b/s390x/unittests.cfg
> index 8e52f560..d2740a40 100644
> --- a/s390x/unittests.cfg
> +++ b/s390x/unittests.cfg
> @@ -113,6 +113,9 @@ file = mvpg-sie.elf
>   [spec_ex-sie]
>   file = spec_ex-sie.elf
>   
> +[spec_ex]
> +file = spec_ex.elf
> +
>   [firq-linear-cpu-ids-kvm]
>   file = firq.elf
>   timeout = 20