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

From: Richard Henderson
Subject: Re: [PATCH v4] s390x/tcg: MVCL: Exit to main loop if requested
Date: Wed, 9 Oct 2019 08:13:18 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0

On 10/9/19 7:00 AM, David Hildenbrand wrote:
> 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>
> ---
> v3 -> v4:
> - Switch to cpu_loop_exit_requested() and perform the actual exit in the
>   caller

Reviewed-by: Richard Henderson <address@hidden>


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