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From: | Richard Henderson |
Subject: | Re: [Qemu-devel] [PATCH v2 1/6] target/s390x: Implement STORE FACILITIES LIST EXTENDED |
Date: | Tue, 9 May 2017 09:28:13 -0700 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 |
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~
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