linux-kernel - Re: [PATCH v4 03/14] KVM: s390: pv: avoid stalls for kvm_s390_pv_init

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Message-ID: <efa07fc5-2f74-d785-e90f-571698ae8f54@de.ibm.com>
Date:   Tue, 31 Aug 2021 16:10:19 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org
Cc:     cohuck@...hat.com, frankja@...ux.ibm.com, thuth@...hat.com,
        pasic@...ux.ibm.com, david@...hat.com, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ulrich.Weigand@...ibm.com
Subject: Re: [PATCH v4 03/14] KVM: s390: pv: avoid stalls for
 kvm_s390_pv_init_vm



On 18.08.21 15:26, Claudio Imbrenda wrote:
> When the system is heavily overcommitted, kvm_s390_pv_init_vm might
> generate stall notifications.
> 
> Fix this by using uv_call_sched instead of just uv_call. This is ok because
> we are not holding spinlocks.

I guess this should only happen for really large guests where the donated memory is also large?
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> Fixes: 214d9bbcd3a672 ("s390/mm: provide memory management functions for protected KVM guests")

Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>

> ---
>   arch/s390/kvm/pv.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> index 0a854115100b..00d272d134c2 100644
> --- a/arch/s390/kvm/pv.c
> +++ b/arch/s390/kvm/pv.c
> @@ -195,7 +195,7 @@ int kvm_s390_pv_init_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
>   	uvcb.conf_base_stor_origin = (u64)kvm->arch.pv.stor_base;
>   	uvcb.conf_virt_stor_origin = (u64)kvm->arch.pv.stor_var;
>   
> -	cc = uv_call(0, (u64)&uvcb);
> +	cc = uv_call_sched(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",
>