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

[Pierre Morel]

On 19/12/2018 20:17, Michael Mueller 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@xxxxxxxxxxxxx>
> ---
>   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);
> +
> +	return 0;
>   }

Personal opinion, but this function do more than just getting the IPM, 
shouldn't it be reflected in the function name?

>   
>   static inline void clear_ipm_gisc(struct kvm_s390_gisa *gisa, u32 gisc)
> @@ -277,7 +301,7 @@ static inline unsigned long pending_irqs(struct kvm_vcpu *vcpu, u16 irq_flags)
>   	if (irq_flags & IRQ_FLAG_FLOATING)
>   		pending_irqs |= vcpu->kvm->arch.float_int.pending_irqs;
>   	if (irq_flags & IRQ_FLAG_GISA)
> -		pending_irqs |= get_ipm(vcpu->kvm->arch.gisa) <<
> +		pending_irqs |= get_ipm(vcpu->kvm->arch.gisa, irq_flags) <<
>   			IRQ_PEND_IO_ISC_7;
>   	return pending_irqs;
>   }
> @@ -1574,7 +1598,7 @@ static int get_top_gisa_isc(struct kvm *kvm, u64 isc_mask, u32 schid)
>   	if (!kvm->arch.gisa)
>   		goto out;
>   
> -	active_mask = (isc_mask & get_ipm(kvm->arch.gisa) << 24) << 32;
> +	active_mask = (isc_mask & get_ipm(kvm->arch.gisa, IRQ_FLAG_IAM) << 24) << 32;

why do we need to set the IAM here?

>   	while (active_mask) {
>   		isc = __fls(active_mask) ^ (BITS_PER_LONG - 1);
>   		if (tac_ipm_gisc(kvm->arch.gisa, isc))
> @@ -2060,7 +2084,7 @@ static int get_all_floating_irqs(struct kvm *kvm, u8 __user *usrbuf, u64 len)
>   	max_irqs = len / sizeof(struct kvm_s390_irq);
>   
>   	if (kvm->arch.gisa &&
> -	    get_ipm(kvm->arch.gisa)) {
> +	    get_ipm(kvm->arch.gisa, IRQ_FLAG_IAM)) {

and here?

>   		for (i = 0; i <= MAX_ISC; i++) {
>   			if (n == max_irqs) {
>   				/* signal userspace to try again */


--
Pierre Morel
Linux/KVM/QEMU in BÃblingen - Germany