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

Pierre Morel
2019-01-03T15:06:37Z

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@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);
> +
> + 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 Böblingen - Germany