linux-kernel - Re: [PATCH v3 1/2] s390/setup: diag318: remove bit check and refactor struct

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Message-Id: <39632665-8861-a386-a1c9-9ce9d081f868@linux.ibm.com>
Date:   Wed, 3 Apr 2019 08:36:28 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Collin Walling <walling@...ux.ibm.com>, pbonzini@...hat.com,
        david@...hat.com, cohuck@...hat.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Cc:     schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
        borntraeger@...ibm.com
Subject: Re: [PATCH v3 1/2] s390/setup: diag318: remove bit check and refactor
 struct

On 02.04.19 19:46, Collin Walling wrote:
> Execution of DIAGNOSE 0x318 is fenced by checking an SCLP bit
> for the availability of hardware support for the instruction.
> 
> In order to support this instruction for a KVM/QEMU guest, we
> would need to provide modifications to the SCLP Read SCP Info
> data, which will in turn reduce the maximum number of CPUs that
> may be provided to the guest. This issue introduces compatability
> and legacy concerns.

s/compatability/compatibility/

> 
> Let's circumvent this issue by removing the bit check and blindly
> executing the instruction. An exception table rule is in place to
> catch the case where hardware does not support this instruction.

Great, another ESSA like instruction...
The sclp bit is still there but we can choose to ignore it for a spec
exception.

> 
> While we're at it, let's condense the version code fields in the
> diag318_info struct until we can determine how it will be used.
> 
> This modifies commit 4ad78b8651aacf26b3ab6d1e784952eb70469c43
> 
> Signed-off-by: Collin Walling <walling@...ux.ibm.com>



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