Re: [PATCH v6 11/13] KVM: s390: add functions to (un)register GISC with GISA

[Pierre Morel <pmorel@linux.ibm.com>]

On 24/01/2019 13:59, Michael Mueller wrote:
> Add the Interruption Alert Mask (IAM) to the architecture specific
> kvm struct. This mask in the GISA is used to define for which ISC
> a GIB alert will be issued.
> 
> The functions kvm_s390_gisc_register() and kvm_s390_gisc_unregister()
> are used to (un)register a GISC (guest ISC) with a virtual machine and
> its GISA.
> 
> Upon successful completion, kvm_s390_gisc_register() returns the
> ISC to be used for GIB alert interruptions. A negative return code
> indicates an error during registration.
> 
> Theses functions will be used by other adapter types like AP and PCI to
> request pass-through interruption support.
> 
> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
> ---
>   arch/s390/include/asm/kvm_host.h |  13 +++++
>   arch/s390/kvm/interrupt.c        | 117 +++++++++++++++++++++++++++++++++++++++
>   2 files changed, 130 insertions(+)
> 
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 7077762ab460..2cfff617cb21 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -781,6 +781,9 @@ struct kvm_s390_gisa {
>   			u8  reserved03[11];
>   			u32 airq_count;
>   		} g1;
> +		struct {
> +			u64 word[4];
> +		} u64;
>   	};
>   };
>   
> @@ -813,8 +816,15 @@ struct kvm_s390_vsie {
>   	struct page *pages[KVM_MAX_VCPUS];
>   };
>   
> +struct kvm_s390_gisa_iam {
> +	u8 mask;
> +	spinlock_t ref_lock;
> +	u32 ref_count[MAX_ISC + 1];
> +};
> +
>   struct kvm_s390_gisa_interrupt {
>   	struct kvm_s390_gisa *origin;
> +	struct kvm_s390_gisa_iam alert;
>   };
>   
>   struct kvm_arch{
> @@ -885,6 +895,9 @@ void kvm_arch_crypto_set_masks(struct kvm *kvm, unsigned long *apm,
>   extern int sie64a(struct kvm_s390_sie_block *, u64 *);
>   extern char sie_exit;
>   
> +extern int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc);
> +extern int kvm_s390_gisc_unregister(struct kvm *kvm, u32 gisc);
> +
>   static inline void kvm_arch_hardware_disable(void) {}
>   static inline void kvm_arch_check_processor_compat(void *rtn) {}
>   static inline void kvm_arch_sync_events(struct kvm *kvm) {}
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index 5efcd9e2cf8f..6bc9dab6d352 100644
> --- a/arch/s390/kvm/interrupt.c
> +++ b/arch/s390/kvm/interrupt.c
> @@ -222,6 +222,33 @@ static inline u8 int_word_to_isc(u32 int_word)
>    */
>   #define IPM_BIT_OFFSET (offsetof(struct kvm_s390_gisa, ipm) * BITS_PER_BYTE)
>   
> +/**
> + * gisa_set_iam - change the GISA interruption alert mask
> + *
> + * @gisa: gisa to operate on
> + * @iam: new IAM value to use
> + *
> + * Change the IAM atomically with the next alert address and the IPM
> + * of the GISA if the GISA is not part of the GIB alert list. All three
> + * fields are located in the first long word of the GISA.
> + *
> + * Returns: 0 on success
> + *          -EBUSY in case the gisa is part of the alert list
> + */
> +static inline int gisa_set_iam(struct kvm_s390_gisa *gisa, u8 iam)
> +{
> +	u64 word, _word;
> +
> +	do {
> +		word = READ_ONCE(gisa->u64.word[0]);
> +		if ((u64)gisa != word >> 32)
> +			return -EBUSY;
> +		_word = (word & ~0xffUL) | iam;
> +	} while (cmpxchg(&gisa->u64.word[0], word, _word) != word);
> +
> +	return 0;
> +}
> +
>   static inline void gisa_set_ipm_gisc(struct kvm_s390_gisa *gisa, u32 gisc)
>   {
>   	set_bit_inv(IPM_BIT_OFFSET + gisc, (unsigned long *) gisa);
> @@ -2911,6 +2938,8 @@ void kvm_s390_gisa_init(struct kvm *kvm)
>   	if (!css_general_characteristics.aiv)
>   		return;
>   	gi->origin = &kvm->arch.sie_page2->gisa;
> +	gi->alert.mask = 0;
> +	spin_lock_init(&gi->alert.ref_lock);
>   	kvm_s390_gisa_clear(kvm);
>   	VM_EVENT(kvm, 3, "gisa 0x%pK initialized", gi->origin);
>   }
> @@ -2920,6 +2949,94 @@ void kvm_s390_gisa_destroy(struct kvm *kvm)
>   	kvm->arch.gisa_int.origin = NULL;
>   }
>   
> +/**
> + * kvm_s390_gisc_register - register a guest ISC
> + *
> + * @kvm:  the kernel vm to work with
> + * @gisc: the guest interruption sub class to register
> + *
> + * The function extends the vm specific alert mask to use.
> + * The effectve IAM mask in the GISA is updated as well
> + * in case the GISA is not part of the GIB alert list.
> + * It will be updated latest when the IAM gets restored
> + * by gisa_get_ipm_or_restore_iam().
> + *
> + * Returns: the nonspecific ISC (NISC) the gib alert mechanism
> + *          has registered with the channel subsystem.
> + *          -ENODEV in case the vm uses no GISA
> + *          -ERANGE in case the guest ISC is invalid
> + */
> +int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc)
> +{
> +	struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
> +	u8 alert_mask;
> +
> +	if (!gi->origin)
> +		return -ENODEV;
> +	if (gisc > MAX_ISC)
> +		return -ERANGE;
> +
> +	spin_lock(&gi->alert.ref_lock);
> +	if (gi->alert.ref_count[gisc] == 0) {
> +		alert_mask = gi->alert.mask | 0x80 >> gisc;
> +		WRITE_ONCE(gi->alert.mask, alert_mask);

not sure WRITE_ONCE is useful.



> +	}
> +	gi->alert.ref_count[gisc]++;
> +	if (gi->alert.ref_count[gisc] == 1)
> +		gisa_set_iam(gi->origin, alert_mask);

This will trigger a GAL interrupt on first AP interrupt in all cases.
However setting the iam here is simple and the price is not so high.
so... without the WRITE_ONCE in register and in unregister:

Acked-by: Pierre Morel<pmorel@linux.ibm.com>

Pierre

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