linux-kernel - Re: [PATCH v5 14/21] KVM: s390: pci: provide routines for enabling/disabling interrupt forwarding

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Date:   Tue, 5 Apr 2022 09:48:29 -0400
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        linux-s390@...r.kernel.org
Cc:     alex.williamson@...hat.com, cohuck@...hat.com,
        farman@...ux.ibm.com, pmorel@...ux.ibm.com,
        borntraeger@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, frankja@...ux.ibm.com, david@...hat.com,
        imbrenda@...ux.ibm.com, vneethv@...ux.ibm.com,
        oberpar@...ux.ibm.com, freude@...ux.ibm.com, thuth@...hat.com,
        pasic@...ux.ibm.com, pbonzini@...hat.com, corbet@....net,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v5 14/21] KVM: s390: pci: provide routines for
 enabling/disabling interrupt forwarding

On 4/5/22 9:39 AM, Niklas Schnelle wrote:
> On Mon, 2022-04-04 at 13:43 -0400, Matthew Rosato wrote:
>> These routines will be wired into a kvm ioctl in order to respond to
>> requests to enable / disable a device for Adapter Event Notifications /
>> Adapter Interuption Forwarding.
>>
>> Signed-off-by: Matthew Rosato <mjrosato@...ux.ibm.com>
>> ---
>>   arch/s390/kvm/pci.c      | 247 +++++++++++++++++++++++++++++++++++++++
>>   arch/s390/kvm/pci.h      |   1 +
>>   arch/s390/pci/pci_insn.c |   1 +
>>   3 files changed, 249 insertions(+)
>>
>> diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
>> index 01bd8a2f503b..f0fd68569a9d 100644
>> --- a/arch/s390/kvm/pci.c
>> +++ b/arch/s390/kvm/pci.c
>> @@ -11,6 +11,7 @@
>>   #include <linux/pci.h>
>>   #include <asm/pci.h>
>>   #include <asm/pci_insn.h>
>> +#include <asm/pci_io.h>
>>   #include "pci.h"
>>   
>>   struct zpci_aift *aift;
>> @@ -152,6 +153,252 @@ int kvm_s390_pci_aen_init(u8 nisc)
>>   	return rc;
>>   }
>>   
>> +/* Modify PCI: Register floating adapter interruption forwarding */
>> +static int kvm_zpci_set_airq(struct zpci_dev *zdev)
>> +{
>> +	u64 req = ZPCI_CREATE_REQ(zdev->fh, 0, ZPCI_MOD_FC_REG_INT);
>> +	struct zpci_fib fib = {};
> 
> Hmm this one uses '{}' as initializer while all current callers of
> zpci_mod_fc() use '{0}'. As far as I know the empty braces are a GNU
> extension so should work for the kernel but for consistency I'd go with
> '{0}' or possibly '{.foo = bar, ...}' where that is more readable.
> There too uninitialized fields will be set to 0. Unless of course there
> is a conflicting KVM convention that I don't know about.

No convention that I'm aware of, I previously had fib = {0} based on the 
same rationale you describe and changed to fib = {} per review request 
from Pierre a few versions back.  I don't have a strong preference, but 
I did not note any functional difference between the two and see a bunch 
of examples of both methods throughout the kernel.