Re: [kvm-unit-tests PATCH v2 1/8] s390x: uv-host: Add access checks for donated memory

[Steffen Eiden <seiden@linux.ibm.com>]

Hi Janosch,

On 7/6/22 08:40, Janosch Frank wrote:
> Let's check if the UV really protected all the memory we donated.
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> ---
>   s390x/uv-host.c | 29 +++++++++++++++++++++++++++++
>   1 file changed, 29 insertions(+)
> 
> diff --git a/s390x/uv-host.c b/s390x/uv-host.c
> index a1a6d120..983cb4a1 100644
> --- a/s390x/uv-host.c
> +++ b/s390x/uv-host.c
> @@ -43,6 +43,24 @@ static void cpu_loop(void)
>   	for (;;) {}
>   }
>   
> +/*
> + * Checks if a memory area is protected as secure memory.
> + * Will return true if all pages are protected, false otherwise.
> + */
> +static bool access_check_3d(uint64_t *access_ptr, uint64_t len)
> +{
> +	while (len) {
> +		expect_pgm_int();
> +		*access_ptr += 42;
> +		if (clear_pgm_int() != PGM_INT_CODE_SECURE_STOR_ACCESS)
> +			return false;
> +		access_ptr += PAGE_SIZE / sizeof(access_ptr);
> +		len -= PAGE_SIZE;
If someone uses this function with 'len' not being a multiple of
PAGE_SIZE this test does not for what is was intended by testing more 
memory than expected.

I suggest adding an explicit assert at the beginning of the function
that ensures 'len' is a multiple of PAGE_SIZE.

> +	}
> +
> +	return true;
> +}
> +

[snip]

Steffen