Re: [PATCH v3 2/4] KVM: s390: Remove cond_resched() calls

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Thu, 30 Jul 2026 07:29:05 +0200
Heiko Carstens <hca@linux.ibm.com> wrote:

> Since [1] cond_resched() is a no-op on s390. Remove all calls.
> 
> This also entirely removes uv_call_sched() and replaces all call sites
> with uv_call(), since both functions are identical after the removal
> of cond_resched().
> 
> [1] commit 7dadeaa6e851 ("sched: Further restrict the preemption modes")
> 
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> ---
>  arch/s390/include/asm/uv.h   | 16 ++--------------
>  arch/s390/kernel/uv.c        |  2 +-
>  arch/s390/kvm/gaccess.c      |  8 ++------
>  arch/s390/kvm/gmap.c         |  4 ----
>  arch/s390/kvm/kvm-s390.c     |  1 -
>  arch/s390/kvm/pv.c           | 11 +++++------
>  arch/s390/kvm/vsie.c         |  1 -
>  arch/s390/mm/gmap_helpers.c  |  1 -
>  drivers/s390/char/uvdevice.c |  6 +++---
>  9 files changed, 13 insertions(+), 37 deletions(-)
> 
> diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
> index d919e69662f5..89c9bb56c7e6 100644
> --- a/arch/s390/include/asm/uv.h
> +++ b/arch/s390/include/asm/uv.h
> @@ -454,18 +454,6 @@ static inline int uv_call(unsigned long r1, unsigned long r2)
>  	return cc;
>  }
>  
> -/* Low level uv_call that avoids stalls for long running busy conditions  */
> -static inline int uv_call_sched(unsigned long r1, unsigned long r2)
> -{
> -	int cc;
> -
> -	do {
> -		cc = __uv_call(r1, r2);
> -		cond_resched();
> -	} while (cc > 1);
> -	return cc;
> -}
> -
>  /*
>   * special variant of uv_call that only transports the cpu or guest
>   * handle and the command, like destroy or verify.
> @@ -480,7 +468,7 @@ static inline int uv_cmd_nodata(u64 handle, u16 cmd, u16 *rc, u16 *rrc)
>  	int cc;
>  
>  	WARN(!handle, "No handle provided to Ultravisor call cmd %x\n", cmd);
> -	cc = uv_call_sched(0, (u64)&uvcb);
> +	cc = uv_call(0, (u64)&uvcb);
>  	*rc = uvcb.header.rc;
>  	*rrc = uvcb.header.rrc;
>  	return cc ? -EINVAL : 0;
> @@ -518,7 +506,7 @@ static inline int uv_list_secrets(struct uv_secret_list *buf, u16 start_idx,
>  		.start_idx = start_idx,
>  		.list_addr = (u64)buf,
>  	};
> -	int cc = uv_call_sched(0, (u64)&uvcb);
> +	int cc = uv_call(0, (u64)&uvcb);
>  
>  	if (rc)
>  		*rc = uvcb.header.rc;
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index a284f98d9716..62841bb00a26 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -831,7 +831,7 @@ int uv_retrieve_secret(u16 secret_idx, u8 *buf, size_t buf_size)
>  		.buf_size = buf_size,
>  	};
>  
> -	uv_call_sched(0, (u64)&uvcb);
> +	uv_call(0, (u64)&uvcb);
>  
>  	switch (uvcb.header.rc) {
>  	case UVC_RC_EXECUTED:
> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
> index 36102b2727fb..0d389a302a70 100644
> --- a/arch/s390/kvm/gaccess.c
> +++ b/arch/s390/kvm/gaccess.c
> @@ -151,10 +151,8 @@ static void ipte_lock_simple(struct kvm *kvm)
>  	ic = &kvm->arch.sca->ipte_control;
>  	old = READ_ONCE(*ic);
>  	do {
> -		if (old.k) {
> -			cond_resched();
> +		if (old.k)
>  			goto retry;
> -		}
>  		new = old;
>  		new.k = 1;
>  	} while (!try_cmpxchg(&ic->val, &old.val, new.val));
> @@ -189,10 +187,8 @@ static void ipte_lock_siif(struct kvm *kvm)
>  	ic = &kvm->arch.sca->ipte_control;
>  	old = READ_ONCE(*ic);
>  	do {
> -		if (old.kg) {
> -			cond_resched();
> +		if (old.kg)
>  			goto retry;
> -		}
>  		new = old;
>  		new.k = 1;
>  		new.kh++;
> diff --git a/arch/s390/kvm/gmap.c b/arch/s390/kvm/gmap.c
> index 8abb4f55b306..3758e4009709 100644
> --- a/arch/s390/kvm/gmap.c
> +++ b/arch/s390/kvm/gmap.c
> @@ -941,7 +941,6 @@ void gmap_split_huge_pages(struct gmap *gmap)
>  		scoped_guard(read_lock, &gmap->kvm->mmu_lock)
>  			start = _dat_walk_gfn_range(start, asce_end(gmap->asce), gmap->asce,
>  						    &ops, DAT_WALK_IGN_HOLES, gmap);
> -		cond_resched();
>  	} while (start);
>  }
>  
> @@ -963,7 +962,6 @@ static int _gmap_enable_skeys(struct gmap *gmap)
>  	do {
>  		scoped_guard(write_lock, &gmap->kvm->mmu_lock)
>  			start = dat_reset_skeys(gmap->asce, start);
> -		cond_resched();
>  	} while (start);
>  	return 0;
>  }
> @@ -1019,7 +1017,6 @@ int gmap_pv_destroy_range(struct gmap *gmap, gfn_t start, gfn_t end, bool interr
>  						    DAT_WALK_IGN_HOLES, NULL);
>  		if (interruptible && fatal_signal_pending(current))
>  			return -EINTR;
> -		cond_resched();
>  	} while (start && start < end);
>  	return 0;
>  }
> @@ -1138,7 +1135,6 @@ void _gmap_set_cmma_all(struct gmap *gmap, bool dirty)
>  			gfn = _dat_walk_gfn_range(gfn, asce_end(gmap->asce), gmap->asce, &ops,
>  						  DAT_WALK_IGN_HOLES,
>  						  &gmap->kvm->arch.cmma_dirty_pages);
> -		cond_resched();
>  	} while (gfn);
>  }
>  
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 150b5dd2170e..2ede8f035a38 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -1027,7 +1027,6 @@ static int kvm_s390_set_mem_control(struct kvm *kvm, struct kvm_device_attr *att
>  		do {
>  			scoped_guard(read_lock, &kvm->mmu_lock)
>  				start_gfn = dat_reset_cmma(kvm->arch.gmap->asce, start_gfn);
> -			cond_resched();
>  		} while (start_gfn);
>  		ret = 0;
>  		break;
> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> index 1beacc841ca8..54c17ddb6b11 100644
> --- a/arch/s390/kvm/pv.c
> +++ b/arch/s390/kvm/pv.c
> @@ -429,7 +429,7 @@ static int kvm_s390_pv_deinit_vm_fast(struct kvm *kvm, u16 *rc, u16 *rrc)
>  	};
>  	int cc;
>  
> -	cc = uv_call_sched(0, (u64)&uvcb);
> +	cc = uv_call(0, (u64)&uvcb);
>  	if (rc)
>  		*rc = uvcb.header.rc;
>  	if (rrc)
> @@ -746,7 +746,7 @@ int kvm_s390_pv_init_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
>  	}
>  	gmap_split_huge_pages(kvm->arch.gmap);
>  
> -	cc = uv_call_sched(0, (u64)&uvcb);
> +	cc = uv_call(0, (u64)&uvcb);
>  	*rc = uvcb.header.rc;
>  	*rrc = uvcb.header.rrc;
>  	KVM_UV_EVENT(kvm, 3, "PROTVIRT CREATE VM: handle %llx len %llx rc %x rrc %x flags %04x",
> @@ -832,7 +832,6 @@ int kvm_s390_pv_unpack(struct kvm *kvm, unsigned long addr, unsigned long size,
>  	while (offset < size) {
>  		ret = unpack_one(kvm, addr, tweak, offset, rc, rrc);
>  		if (ret == -EAGAIN) {
> -			cond_resched();
>  			if (fatal_signal_pending(current))
>  				break;
>  			continue;
> @@ -875,7 +874,7 @@ int kvm_s390_pv_dump_cpu(struct kvm_vcpu *vcpu, void *buff, u16 *rc, u16 *rrc)
>  	};
>  	int cc;
>  
> -	cc = uv_call_sched(0, (u64)&uvcb);
> +	cc = uv_call(0, (u64)&uvcb);
>  	*rc = uvcb.header.rc;
>  	*rrc = uvcb.header.rrc;
>  	return cc;
> @@ -959,7 +958,7 @@ int kvm_s390_pv_dump_stor_state(struct kvm *kvm, void __user *buff_user,
>  	/* We will loop until the user buffer is filled or an error occurs */
>  	do {
>  		/* Get 1MB worth of guest storage state data */
> -		cc = uv_call_sched(0, (u64)&uvcb);
> +		cc = uv_call(0, (u64)&uvcb);
>  
>  		/* All or nothing */
>  		if (cc) {
> @@ -1037,7 +1036,7 @@ int kvm_s390_pv_dump_complete(struct kvm *kvm, void __user *buff_user,
>  		return -ENOMEM;
>  	complete.dump_area_origin = (u64)compl_data;
>  
> -	ret = uv_call_sched(0, (u64)&complete);
> +	ret = uv_call(0, (u64)&complete);
>  	*rc = complete.header.rc;
>  	*rrc = complete.header.rrc;
>  	KVM_UV_EVENT(kvm, 3, "PROTVIRT DUMP COMPLETE: rc %x rrc %x",
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index eea24562e7db..6dcd3b110c17 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -1434,7 +1434,6 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>  		}
>  		if (sg)
>  			sg = gmap_put(sg);
> -		cond_resched();
>  	}
>  	if (sg)
>  		sg = gmap_put(sg);
> diff --git a/arch/s390/mm/gmap_helpers.c b/arch/s390/mm/gmap_helpers.c
> index 4bf7c9012feb..d564cdefb90f 100644
> --- a/arch/s390/mm/gmap_helpers.c
> +++ b/arch/s390/mm/gmap_helpers.c
> @@ -272,7 +272,6 @@ static int __gmap_helper_unshare_zeropages(struct mm_struct *mm)
>  		 * truncation. In that case, the shared zeropage would be gone
>  		 * and we can simply retry and make progress.
>  		 */
> -		cond_resched();
>  		goto retry;
>  	}
>  
> diff --git a/drivers/s390/char/uvdevice.c b/drivers/s390/char/uvdevice.c
> index e6a264c996ce..4d274a2ee84d 100644
> --- a/drivers/s390/char/uvdevice.c
> +++ b/drivers/s390/char/uvdevice.c
> @@ -224,7 +224,7 @@ static int uvio_attestation(struct uvio_ioctl_cb *uv_ioctl)
>  	if (ret)
>  		goto out;
>  
> -	uv_call_sched(0, (u64)uvcb_attest);
> +	uv_call(0, (u64)uvcb_attest);
>  
>  	uv_ioctl->uv_rc = uvcb_attest->header.rc;
>  	uv_ioctl->uv_rrc = uvcb_attest->header.rrc;
> @@ -291,7 +291,7 @@ static int uvio_add_secret(struct uvio_ioctl_cb *uv_ioctl)
>  
>  	ret = 0;
>  	uvcb.addr = (u64)asrcb;
> -	uv_call_sched(0, (u64)&uvcb);
> +	uv_call(0, (u64)&uvcb);
>  	uv_ioctl->uv_rc = uvcb.header.rc;
>  	uv_ioctl->uv_rrc = uvcb.header.rrc;
>  
> @@ -457,7 +457,7 @@ static int uvio_retr_secret(struct uvio_ioctl_cb *uv_ioctl)
>  
>  	uvcb.buf_addr = (u64)buf;
>  	uvcb.buf_size = buf_len;
> -	uv_call_sched(0, (u64)&uvcb);
> +	uv_call(0, (u64)&uvcb);
>  
>  	if (copy_to_user((__user void *)uv_ioctl->argument_addr, buf, buf_len))
>  		goto err;