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Re: [qemu-s390x] [kvm-unit-tests PATCH 2/5] s390x: Switch to z/Arch if n
Re: [qemu-s390x] [kvm-unit-tests PATCH 2/5] s390x: Switch to z/Arch if needed
Wed, 5 Dec 2018 11:15:32 +0100
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On 05.12.18 10:45, David Hildenbrand wrote:
> On 04.12.18 14:48, Janosch Frank wrote:
>> LPAR and z/VM start in esam mode, so we need to switch to z/Arch and
>> set 64 bit addressing.
>> Under Qemu/KVM we already start out with both when being run with the
>> Qemu --kernel argument or we lack only 64 bit when booting from disk.
>> Signed-off-by: Janosch Frank <address@hidden>
>> s390x/cstart64.S | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>> diff --git a/s390x/cstart64.S b/s390x/cstart64.S
>> index abd6b58..80dbcba 100644
>> --- a/s390x/cstart64.S
>> +++ b/s390x/cstart64.S
>> @@ -20,6 +20,15 @@
>> .globl start
>> + tam # Test for 64 bit addressing (KVM IPL)
>> + brc 1, start64 # If cc = 3 (64 bit), we have z/Arch
> Looking at the kernel, we don't have to test for 64bit but can simply do
> that always unconditionally. SIGP might bail out but we ignore it. sam64
> will also simply do nothing.
> So tam+brc are not necessary.
Right, sigp will be a nop with inv parm and inc state as a return.
I guess we don't need to save cycles here so I can get rid of the branch.
>> + /* Switch to z/Architecture mode (64-bit) */
>> + slr %r0, %r0 # set cpuid to zero
>> + lhi %r1, 2 # mode 2 = esame
>> + sigp %r1, %r0, 0x12 # sigp set arch
>> + bras %r13,0f
>> + .fill 16,4,0x0
>> +0: lmh %r0,%r15,0(%r13) # clear high-order half of gprs
> This is just what the kernel does. The ".fill" part is confusing at
> first, but it is just the data loaded into the high-order halfs (all 0s)
> (I was told mixing code and data is bad practice, but for some reason
> people in Linux decided to do it like that (maybe because of some
> relocation thingy? or because of instruction set restrictions?))
Honestly I wouldn't even have considered clearing if I haven't seen it
in the kernel. I could define a zero area at the end of the file or do
an lm targeting the cleared bss right before jumping into setup. Or we
could do 16 xc register to register :)
> Should we introduce defines for SIGPs? We might have more once we
> support multiple CPUs eiher way.
We also have sigp stop so why not.
How about making the indent patch a cleanup patch and adding all
>> sam64 # Set addressing mode to 64 bit
>> /* setup stack */
Description: OpenPGP digital signature
[qemu-s390x] [kvm-unit-tests PATCH 2/5] s390x: Switch to z/Arch if needed, Janosch Frank, 2018/12/04
[qemu-s390x] [kvm-unit-tests PATCH 3/5] s390x: Add BSS clearing for non ELF boot, Janosch Frank, 2018/12/04
[qemu-s390x] [kvm-unit-tests PATCH 4/5] s390x: Use interrupts in SCLP and add line mode, Janosch Frank, 2018/12/04
[qemu-s390x] [kvm-unit-tests PATCH 5/5] s390x: Fix sclp-ascii.c indents, Janosch Frank, 2018/12/04