Re: [Qemu-devel] [PATCH v2 1/6] target/s390x: Implement STORE FACILITIES LIST EXTENDED

[Richard Henderson <rth@twiddle.net>]

On 05/09/2017 08:17 AM, Aurelien Jarno wrote:
> Ok, thanks for the detailed explanations. Then I guess you should fold
> the following patch to correctly set the zArch active bit as done in
> s390_fill_feat_block:
> 
> --- a/target/s390x/misc_helper.c
> +++ b/target/s390x/misc_helper.c
> @@ -693,6 +693,11 @@ static unsigned do_stfle(CPUS390XState *env, uint64_t words[MAX_STFL_WORDS])
>   
>       memset(words, 0, sizeof(uint64_t) * MAX_STFL_WORDS);
>   
> +    if (test_bit(S390_FEAT_ZARCH, features)) {
> +        /* z/Architecture is always active if around */
> +        words[0] |= 1ull << 61;
> +    }

Oops, yes, good catch.

>> Which means that we cannot mask *anything* from TCG, including the useless
>> stuff like hexadecimal floating point, and still have the kernel boot.  So
>> in practice a feature mask for TCG will be not only useless but actively
>> harmful.
> 
> That's true if you want to boot an optimized kernel.

Well, yes.  But the last time I was really looking at this (2 years ago?) 
Fedora was built to use z9-109.  I guess maybe Debian is the only distribution 
that doesn't force some later cpu?

> As soon as you try to
> use a newer CPU like the z990, the DAT-enhancement facility bit is set
> in STFL, and the kernel try to use the idte instruction which is not
> emulated by QEMU.

Good to know.  Thanks,


r~