linux-kernel - Re: [PATCH v2 4/7] s390/physmem_info: query diag500(STORAGE LIMIT) to support QEMU/KVM memory devices

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Message-ID: <ZxC+mr5PcGv4fBcY@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com>
Date: Thu, 17 Oct 2024 09:36:58 +0200
From: Alexander Gordeev <agordeev@...ux.ibm.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
        linux-doc@...r.kernel.org, kvm@...r.kernel.org,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, Thomas Huth <thuth@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Eugenio Pérez <eperezma@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>, Mario Casquero <mcasquer@...hat.com>
Subject: Re: [PATCH v2 4/7] s390/physmem_info: query diag500(STORAGE LIMIT)
 to support QEMU/KVM memory devices

On Mon, Oct 14, 2024 at 04:46:16PM +0200, David Hildenbrand wrote:

Hi David!

> @@ -157,7 +189,9 @@ unsigned long detect_max_physmem_end(void)
>  {
>  	unsigned long max_physmem_end = 0;
>  
> -	if (!sclp_early_get_memsize(&max_physmem_end)) {
> +	if (!diag500_storage_limit(&max_physmem_end)) {
> +		physmem_info.info_source = MEM_DETECT_DIAG500_STOR_LIMIT;
> +	} else if (!sclp_early_get_memsize(&max_physmem_end)) {
>  		physmem_info.info_source = MEM_DETECT_SCLP_READ_INFO;
>  	} else {
>  		max_physmem_end = search_mem_end();
> @@ -170,11 +204,17 @@ void detect_physmem_online_ranges(unsigned long max_physmem_end)
>  {
>  	if (!sclp_early_read_storage_info()) {
>  		physmem_info.info_source = MEM_DETECT_SCLP_STOR_INFO;
> +		return;
>  	} else if (!diag260()) {
>  		physmem_info.info_source = MEM_DETECT_DIAG260;
> -	} else if (max_physmem_end) {
> -		add_physmem_online_range(0, max_physmem_end);
> +		return;
> +	} else if (physmem_info.info_source == MEM_DETECT_DIAG500_STOR_LIMIT) {
> +		max_physmem_end = 0;
> +		if (!sclp_early_get_memsize(&max_physmem_end))
> +			physmem_info.info_source = MEM_DETECT_SCLP_READ_INFO;

Why search_mem_end() is not tried in case sclp_early_get_memsize() failed?

>  	}
> +	if (max_physmem_end)
> +		add_physmem_online_range(0, max_physmem_end);
>  }
>  
>  void physmem_set_usable_limit(unsigned long limit)
> diff --git a/arch/s390/include/asm/physmem_info.h b/arch/s390/include/asm/physmem_info.h
> index f45cfc8bc233..51b68a43e195 100644
> --- a/arch/s390/include/asm/physmem_info.h
> +++ b/arch/s390/include/asm/physmem_info.h
> @@ -9,6 +9,7 @@ enum physmem_info_source {
>  	MEM_DETECT_NONE = 0,
>  	MEM_DETECT_SCLP_STOR_INFO,
>  	MEM_DETECT_DIAG260,
> +	MEM_DETECT_DIAG500_STOR_LIMIT,
>  	MEM_DETECT_SCLP_READ_INFO,
>  	MEM_DETECT_BIN_SEARCH
>  };
> @@ -107,6 +108,8 @@ static inline const char *get_physmem_info_source(void)
>  		return "sclp storage info";
>  	case MEM_DETECT_DIAG260:
>  		return "diag260";
> +	case MEM_DETECT_DIAG500_STOR_LIMIT:
> +		return "diag500 storage limit";

AFAIU you want to always override MEM_DETECT_DIAG500_STOR_LIMIT method
with an online memory detection method. In that case this code is dead.

>  	case MEM_DETECT_SCLP_READ_INFO:
>  		return "sclp read info";
>  	case MEM_DETECT_BIN_SEARCH:

Thanks!