On 02.04.19 19:46, Collin Walling wrote:
> Execution of DIAGNOSE 0x318 is fenced by checking an SCLP bit
> for the availability of hardware support for the instruction.
>
> In order to support this instruction for a KVM/QEMU guest, we
> would need to provide modifications to the SCLP Read SCP Info
> data, which will in turn reduce the maximum number of CPUs that
> may be provided to the guest. This issue introduces compatability
> and legacy concerns.
>
> Let's circumvent this issue by removing the bit check and blindly
> executing the instruction. An exception table rule is in place to
> catch the case where hardware does not support this instruction.
No, please keep the check. We have to extend the read scp field anyway
for future extensions.
>
> While we're at it, let's condense the version code fields in the
> diag318_info struct until we can determine how it will be used.
>
> This modifies commit 4ad78b8651aacf26b3ab6d1e784952eb70469c43
>
> Signed-off-by: Collin Walling <walling@xxxxxxxxxxxxx>
> ---
> arch/s390/include/asm/diag.h | 6 ++----
> arch/s390/kernel/setup.c | 12 ++++++------
> 2 files changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/arch/s390/include/asm/diag.h b/arch/s390/include/asm/diag.h
> index 19562be22b7e..215516284175 100644
> --- a/arch/s390/include/asm/diag.h
> +++ b/arch/s390/include/asm/diag.h
> @@ -298,10 +298,8 @@ struct diag26c_mac_resp {
> union diag318_info {
> unsigned long val;
> struct {
> - unsigned int cpnc : 8;
> - unsigned int cpvc_linux : 24;
> - unsigned char cpvc_distro[3];
> - unsigned char zero;
> + unsigned long cpnc : 8;
> + unsigned long cpvc : 56;
> };
> };
>
> diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
> index 2c642af526ce..fe70201f8b5d 100644
> --- a/arch/s390/kernel/setup.c
> +++ b/arch/s390/kernel/setup.c
> @@ -1011,15 +1011,15 @@ static void __init setup_control_program_code(void)
> {
> union diag318_info diag318_info = {
> .cpnc = CPNC_LINUX,
> - .cpvc_linux = 0,
> - .cpvc_distro = {0},
> + .cpvc = 0,
> };
>
> - if (!sclp.has_diag318)
> - return;
> -
> diag_stat_inc(DIAG_STAT_X318);
> - asm volatile("diag %0,0,0x318\n" : : "d" (diag318_info.val));
> + asm volatile(
> + " diag %0,0,0x318\n"
> + "0: nopr %%r7\n"
> + EX_TABLE(0b,0b)
> + : : "d" (diag318_info.val));
> }
>
> /*
>
