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Reply-To: mimu@linux.ibm.com
Subject: Re: [PATCH v5 11/15] KVM: s390: restore IAM in get_ipm() when IPM is
 clean
To:     Halil Pasic <pasic@linux.ibm.com>
Cc:     KVM Mailing List <kvm@vger.kernel.org>,
        Linux-S390 Mailing List <linux-s390@vger.kernel.org>,
        linux-kernel@vger.kernel.org,
        kvm390-list@tuxmaker.boeblingen.de.ibm.com,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        David Hildenbrand <david@redhat.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Pierre Morel <pmorel@linux.ibm.com>
References: <20181219191756.57973-1-mimu@linux.ibm.com>
 <20181219191756.57973-12-mimu@linux.ibm.com>
 <20190107003244.219e873e@oc2783563651>
From:   Michael Mueller <mimu@linux.ibm.com>
Organization: IBM
Date:   Tue, 8 Jan 2019 09:06:59 +0100
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On 07.01.19 00:32, Halil Pasic wrote:
> On Wed, 19 Dec 2018 20:17:52 +0100
> Michael Mueller <mimu@linux.ibm.com> wrote:
> 
>> The patch adds the parameter irq_flags and allows to
>> restore the Interruption Alert Mask (IAM) in the GISA
>> atomically while guaranteeing the IPM is clean.
>>
>> The function returns the IPM of the GISA. If the returned
>> value is 0x00 and the IRQ_FLAG_IAM was set, the IAM has
>> been restored.
>>
>> New irq flag:
>>    IRQ_FLAG_IAM: When set, the IAM is restored if no ISC bit
>>    		is set in the IPM, i.e. no new airqs are
>> 		pending. The test and restore operations
>> 		are done atomically.
>>
>> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
>> ---
>>   arch/s390/kvm/interrupt.c | 34 +++++++++++++++++++++++++++++-----
>>   1 file changed, 29 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
>> index 1cc3ad2e6c7e..8307717e3caf 100644
>> --- a/arch/s390/kvm/interrupt.c
>> +++ b/arch/s390/kvm/interrupt.c
>> @@ -37,6 +37,7 @@
>>   #define IRQ_FLAG_LOCAL    0x8000 /* include local interruption pending mask */
>>   #define IRQ_FLAG_FLOATING 0x4000 /* include float interruption pending mask */
>>   #define IRQ_FLAG_GISA     0x2000 /* include GISA interruption pending mask */
>> +#define IRQ_FLAG_IAM      0x0080 /* when set try to restore IAM */
>>   
>>   #define IRQ_MASK_ALL      (IRQ_FLAG_LOCAL | IRQ_FLAG_FLOATING | IRQ_FLAG_GISA)
>>   #define IRQ_MASK_NO_GISA  (IRQ_MASK_ALL & ~IRQ_FLAG_GISA)
>> @@ -253,9 +254,32 @@ static inline void set_ipm_gisc(struct kvm_s390_gisa *gisa, u32 gisc)
>>   	set_bit_inv(IPM_BIT_OFFSET + gisc, (unsigned long *) gisa);
>>   }
>>   
>> -static inline u8 get_ipm(struct kvm_s390_gisa *gisa)
>> +static inline u8 get_ipm(struct kvm_s390_gisa *gisa, u16 irq_flags)
>>   {
>> -	return READ_ONCE(gisa->ipm);
>> +	u64 word, _word;
>> +	u8 ipm;
>> +
>> +	if (!(irq_flags & IRQ_FLAG_IAM))
>> +		return READ_ONCE(gisa->ipm);
>> +
>> +	do {
>> +		word = READ_ONCE(gisa->u64.word[0]);
>> +		ipm = word >> 24;
>> +		/* If the GISA is in the alert list, return the IPM. */
>> +		if ((u64)gisa != word >> 32)
>> +			return ipm;
>> +		/* If the IPM is dirty, return the IPM. */
>> +		if (ipm)
>> +			return ipm;
>> +		/*
>> +		 * Try to restore the IAM or loop, if the IPM is dirty
>> +		 * again or the GISA has been inserted into the alert list.
>> +		 */
>> +		_word = (word & ~0xffUL) |
>> +			container_of(gisa, struct sie_page2, gisa)->kvm->arch.iam;
>> +	} while (cmpxchg(&gisa->u64.word[0], word, _word) != _word);
>                                                               ^^
> 
> Shouldn't this rather be:
> 	} while (cmpxchg(&gisa->u64.word[0], word, _word) != word);

Yes, the comparison needs to be done against the old value of
the memory region.

> 
> Regards,
> Halil
>> +
>> +	return 0;
>>   }