Re: [PATCH v5 11/15] KVM: s390: restore IAM in get_ipm() when IPM is clean

[Halil Pasic <pasic@linux.ibm.com>]

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);

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