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Re: [PATCH v4] s390x/tcg: MVCL: Exit to main loop if requested

From: David Hildenbrand
Subject: Re: [PATCH v4] s390x/tcg: MVCL: Exit to main loop if requested
Date: Thu, 10 Oct 2019 12:25:54 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0

On 10.10.19 10:26, Alex Bennée wrote:
> David Hildenbrand <address@hidden> writes:
>> MVCL is interruptible and we should check for interrupts and process
>> them after writing back the variables to the registers. Let's check
>> for any exit requests and exit to the main loop. Introduce a new helper
>> function for that: cpu_loop_exit_requested().
>> When booting Fedora 30, I can see a handful of these exits and it seems
>> to work reliable. Also, Richard explained why this works correctly even
>> when MVCL is called via EXECUTE:
>>     (1) TB with EXECUTE runs, at address Ae
>>         - env->psw_addr stored with Ae.
>>         - helper_ex() runs, memory address Am computed
>>           from D2a(X2a,B2a) or from psw.addr+RI2.
>>         - env->ex_value stored with memory value modified by R1a
>>     (2) TB of executee runs,
>>         - env->ex_value stored with 0.
>>         - helper_mvcl() runs, using and updating R1b, R1b+1, R2b, R2b+1.
>>     (3a) helper_mvcl() completes,
>>          - TB of executee continues, psw.addr += ilen.
>>          - Next instruction is the one following EXECUTE.
>>     (3b) helper_mvcl() exits to main loop,
>>          - cpu_loop_exit_restore() unwinds psw.addr = Ae.
>>          - Next instruction is the EXECUTE itself...
>>          - goto 1.
>> As the PoP mentiones that an interruptible instruction called via EXECUTE
>> should avoid modifying storage/registers that are used by EXECUTE itself,
>> it is fine to retrigger EXECUTE.
>> Cc: Alex Bennée <address@hidden>
>> Cc: Peter Maydell <address@hidden>
>> Cc: Paolo Bonzini <address@hidden>
>> Suggested-by: Richard Henderson <address@hidden>
>> Signed-off-by: David Hildenbrand <address@hidden>
> Reviewed-by: Alex Bennée <address@hidden>


Queued to

https://github.com/davidhildenbrand/qemu.git s390-tcg-next



David / dhildenb

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