linux-kernel - Re: [PATCH v6 09/17] KVM: s390: pv: clear the state without memset

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Date:   Thu, 13 Jan 2022 11:30:13 +0100
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org
Cc:     cohuck@...hat.com, borntraeger@...ibm.com, thuth@...hat.com,
        pasic@...ux.ibm.com, david@...hat.com, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 09/17] KVM: s390: pv: clear the state without memset

On 12/3/21 17:58, Claudio Imbrenda wrote:
> Do not use memset to clean the whole struct kvm_s390_pv; instead,
> explicitly clear the fields that need to be cleared.
> 
> Upcoming patches will introduce new fields in the struct kvm_s390_pv
> that will not need to be cleared.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> ---
>   arch/s390/kvm/pv.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> index 04aa4a20260b..59da54bd6b21 100644
> --- a/arch/s390/kvm/pv.c
> +++ b/arch/s390/kvm/pv.c
> @@ -16,6 +16,15 @@
>   #include <linux/sched/mm.h>
>   #include "kvm-s390.h"
>   
> +static void kvm_s390_clear_pv_state(struct kvm *kvm)
> +{
> +	kvm->arch.pv.handle = 0;
> +	kvm->arch.pv.guest_len = 0;
> +	kvm->arch.pv.stor_base = 0;
> +	kvm->arch.pv.stor_var = NULL;
> +	kvm->arch.pv.handle = 0;

We could use the same approach that we use in qemu to do the cpu resets.
But maybe that would be overkill for a few struct members.

> +}
> +
>   int kvm_s390_pv_destroy_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
>   {
>   	int cc;
> @@ -110,7 +119,7 @@ static void kvm_s390_pv_dealloc_vm(struct kvm *kvm)
>   	vfree(kvm->arch.pv.stor_var);
>   	free_pages(kvm->arch.pv.stor_base,
>   		   get_order(uv_info.guest_base_stor_len));
> -	memset(&kvm->arch.pv, 0, sizeof(kvm->arch.pv));
> +	kvm_s390_clear_pv_state(kvm);
>   }
>   
>   static int kvm_s390_pv_alloc_vm(struct kvm *kvm)
>