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Subject: Re: [PATCH 1/2] s390: uv: Fix sysfs max number of VCPUs reporting
To:     Janosch Frank <frankja@linux.ibm.com>, linux-kernel@vger.kernel.org
Cc:     kvm@vger.kernel.org, thuth@redhat.com, david@redhat.com,
        imbrenda@linux.ibm.com, cohuck@redhat.com,
        linux-s390@vger.kernel.org, gor@linux.ibm.com,
        mihajlov@linux.ibm.com
References: <20210119100402.84734-1-frankja@linux.ibm.com>
 <20210119100402.84734-2-frankja@linux.ibm.com>
From:   Christian Borntraeger <borntraeger@de.ibm.com>
Message-ID: <d72e2823-f30f-02be-1ee5-445496ca9dbc@de.ibm.com>
Date:   Tue, 19 Jan 2021 11:11:55 +0100
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On 19.01.21 11:04, Janosch Frank wrote:
> The number reported by the query is N-1 and I think people reading the
> sysfs file would expect N instead. For users creating VMs there's no
> actual difference because KVM's limit is currently below the UV's
> limit.
> 
> The naming of the field is a bit misleading. Number in this context is
> used like ID and starts at 0. The query field denotes the maximum
> number that can be put into the VCPU number field in the "create
> secure CPU" UV call.
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> Fixes: a0f60f8431999 ("s390/protvirt: Add sysfs firmware interface for Ultravisor information")
> Cc: stable@vger.kernel.org
> ---
>  arch/s390/boot/uv.c        | 2 +-
>  arch/s390/include/asm/uv.h | 4 ++--
>  arch/s390/kernel/uv.c      | 2 +-
>  3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/s390/boot/uv.c b/arch/s390/boot/uv.c
> index a15c033f53ca..afb721082989 100644
> --- a/arch/s390/boot/uv.c
> +++ b/arch/s390/boot/uv.c
> @@ -35,7 +35,7 @@ void uv_query_info(void)
>  		uv_info.guest_cpu_stor_len = uvcb.cpu_stor_len;
>  		uv_info.max_sec_stor_addr = ALIGN(uvcb.max_guest_stor_addr, PAGE_SIZE);
>  		uv_info.max_num_sec_conf = uvcb.max_num_sec_conf;
> -		uv_info.max_guest_cpus = uvcb.max_guest_cpus;
> +		uv_info.max_guest_cpu_id = uvcb.max_guest_cpu_num;
>  	}
>  
>  #ifdef CONFIG_PROTECTED_VIRTUALIZATION_GUEST
> diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
> index 0325fc0469b7..c484c95ea142 100644
> --- a/arch/s390/include/asm/uv.h
> +++ b/arch/s390/include/asm/uv.h
> @@ -96,7 +96,7 @@ struct uv_cb_qui {
>  	u32 max_num_sec_conf;
>  	u64 max_guest_stor_addr;
>  	u8  reserved88[158 - 136];
> -	u16 max_guest_cpus;
> +	u16 max_guest_cpu_num;

I think it would read better if we name this also max_guest_cpu_id.
Otherwise this looks good.