On Fri, Nov 03, 2023 at 10:29:36AM +0100, Nico Boehr wrote:
> Since we now have the ability to run guests without MSO/MSL, add a test
> to make sure this doesn't break.
>
> Signed-off-by: Nico Boehr <nrb@xxxxxxxxxxxxx>
> Reviewed-by: Thomas Huth <thuth@xxxxxxxxxx>
> ---
> s390x/Makefile | 2 +
> s390x/sie-dat.c | 110 +++++++++++++++++++++++++++++++++++++
> s390x/snippets/c/sie-dat.c | 52 ++++++++++++++++++
> s390x/snippets/c/sie-dat.h | 2 +
> s390x/unittests.cfg | 3 +
> 5 files changed, 169 insertions(+)
> create mode 100644 s390x/sie-dat.c
> create mode 100644 s390x/snippets/c/sie-dat.c
> create mode 100644 s390x/snippets/c/sie-dat.h
...
> +static uint8_t test_page[GUEST_TEST_PAGE_COUNT * PAGE_SIZE] __attribute__((__aligned__(PAGE_SIZE)));
> +
> +static inline void force_exit(void)
> +{
> + asm volatile("diag 0,0,0x44\n");
> +}
> +
> +static inline void force_exit_value(uint64_t val)
> +{
> + asm volatile(
> + "diag %[val],0,0x9c\n"
> + : : [val] "d"(val)
> + );
> +}
> +
> +int main(void)
> +{
> + uint8_t *invalid_ptr;
> +
> + memset(test_page, 0, sizeof(test_page));
> + /* tell the host the page's physical address (we're running DAT off) */
> + force_exit_value((uint64_t)test_page);
> +
> + /* write some value to the page so the host can verify it */
> + for (size_t i = 0; i < GUEST_TEST_PAGE_COUNT; i++)
> + test_page[i * PAGE_SIZE] = 42 + i;
> +
> + /* indicate we've written all pages */
> + force_exit();
> +
> + /* the first unmapped address */
> + invalid_ptr = (uint8_t *)(GUEST_TOTAL_PAGE_COUNT * PAGE_SIZE);
> + *invalid_ptr = 42;
> +
> + /* indicate we've written the non-allowed page (should never get here) */
> + force_exit();
> +
> + return 0;
> +}
The compiler will not necessarily generate the expected code here, since
there is no data dependency between the used inline assemblies and the
memory locations that are changed. That is: the compiler may move the
inline assemblies and/or memory assignments around.
In order to prevent that you could simply add a compiler barrier to both
inline assemblies (add "memory" to the clobber list).
