Re: [kvm-unit-tests PATCH] powerpc: Allow for a custom decr value to be specified to load on decr excp

[Laurent Vivier <lvivier@xxxxxxxxxx>]

On 01/05/2019 09:00, Suraj Jitindar Singh wrote:
> Currently the handler for a decrementer exception will simply reload the
> maximum value (0x7FFFFFFF), which will take ~4 seconds to expire again.
> This means that if a vcpu cedes, it will be ~4 seconds between wakeups.
>
> The h_cede_tm test is testing a known breakage when a guest cedes while
> suspended. To be sure we cede 500 times to check for the bug. However
> since it takes ~4 seconds to be woken up once we've ceded, we only get
> through ~20 iterations before we reach the 90 seconds timeout and the
> test appears to fail.
>
> Add an option when registering the decrementer handler to specify the
> value which should be reloaded by the handler, allowing the timeout to be
> chosen.
>
> Modify the spr test to use the max timeout to preserve existing
> behaviour.
> Modify the h_cede_tm test to use a 10ms timeout to ensure we can perform
> 500 iterations before hitting the 90 second time limit for a test.
>
> This means the h_cede_tm test now succeeds rather than timing out.
>
> Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx>
> ---
>   lib/powerpc/handlers.c | 7 ++++---
>   powerpc/sprs.c         | 3 ++-
>   powerpc/tm.c           | 3 ++-
>   3 files changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/lib/powerpc/handlers.c b/lib/powerpc/handlers.c
> index be8226a..c8721e0 100644
> --- a/lib/powerpc/handlers.c
> +++ b/lib/powerpc/handlers.c
> @@ -12,11 +12,12 @@
>   
>   /*
>    * Generic handler for decrementer exceptions (0x900)
> - * Just reset the decrementer back to its maximum value (0x7FFFFFFF)
> + * Just reset the decrementer back to the value specified when registering the
> + * handler
>    */
> -void dec_except_handler(struct pt_regs *regs __unused, void *data __unused)
> +void dec_except_handler(struct pt_regs *regs __unused, void *data)
>   {
> -	uint32_t dec = 0x7FFFFFFF;
> +	uint64_t dec = *((uint64_t *) data);
>   
>   	asm volatile ("mtdec %0" : : "r" (dec));
>   }
> diff --git a/powerpc/sprs.c b/powerpc/sprs.c
> index 6744bd8..3bd6ac7 100644
> --- a/powerpc/sprs.c
> +++ b/powerpc/sprs.c
> @@ -253,6 +253,7 @@ int main(int argc, char **argv)
>   		0x1234567890ABCDEFULL, 0xFEDCBA0987654321ULL,
>   		-1ULL,
>   	};
> +	uint64_t decr = 0x7FFFFFFF;
>   
>   	for (i = 1; i < argc; i++) {
>   		if (!strcmp(argv[i], "-w")) {
> @@ -288,7 +289,7 @@ int main(int argc, char **argv)
>   		(void) getchar();
>   	} else {
>   		puts("Sleeping...\n");
> -		handle_exception(0x900, &dec_except_handler, NULL);
> +		handle_exception(0x900, &dec_except_handler, &decr);
>   		asm volatile ("mtdec %0" : : "r" (0x3FFFFFFF));
>   		hcall(H_CEDE);
>   	}
> diff --git a/powerpc/tm.c b/powerpc/tm.c
> index bd56baa..0f3f543 100644
> --- a/powerpc/tm.c
> +++ b/powerpc/tm.c
> @@ -95,11 +95,12 @@ static bool enable_tm(void)
>   static void test_h_cede_tm(int argc, char **argv)
>   {
>   	int i;
> +	uint64_t decr = 0x3FFFFF;
>   
>   	if (argc > 2)
>   		report_abort("Unsupported argument: '%s'", argv[2]);
>   
> -	handle_exception(0x900, &dec_except_handler, NULL);
> +	handle_exception(0x900, &dec_except_handler, &decr);

Maybe you should also need here:

    asm volatile ("mtdec %0" : : "r" (decr));

To set the first one to the same values as the following ones?

Thanks,
Laurent