linux-kernel - Re: [PATCH 3/3] s390/mm: Define arch_get_mappable

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Date:   Tue, 8 Dec 2020 16:27:09 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org, david@...hat.com,
        catalin.marinas@....com, linux-arm-kernel@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 3/3] s390/mm: Define arch_get_mappable_range()

On Tue, Dec 08, 2020 at 09:46:18AM +0530, Anshuman Khandual wrote:
> This overrides arch_get_mappabble_range() on s390 platform which will be
> used with recently added generic framework. It drops a redundant similar
> check in vmem_add_mapping() while compensating __segment_load() with a new
> address range check to preserve the existing functionality. It also adds a
> VM_BUG_ON() check that would ensure that memhp_range_allowed() has already
> been called on the hotplug path.
> 
> Cc: Heiko Carstens <hca@...ux.ibm.com>
> Cc: Vasily Gorbik <gor@...ux.ibm.com>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: linux-s390@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  arch/s390/mm/extmem.c |  5 +++++
>  arch/s390/mm/init.c   | 10 ++++++++++
>  arch/s390/mm/vmem.c   |  4 ----
>  3 files changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/s390/mm/extmem.c b/arch/s390/mm/extmem.c
> index 5060956b8e7d..cc055a78f7b6 100644
> --- a/arch/s390/mm/extmem.c
> +++ b/arch/s390/mm/extmem.c
> @@ -337,6 +337,11 @@ __segment_load (char *name, int do_nonshared, unsigned long *addr, unsigned long
>  		goto out_free_resource;
>  	}
>  
> +	if (seg->end + 1 > VMEM_MAX_PHYS || seg->end + 1 < seg->start_addr) {
> +		rc = -ERANGE;
> +		goto out_resource;
> +	}
> +
>  	rc = vmem_add_mapping(seg->start_addr, seg->end - seg->start_addr + 1);
>  	if (rc)
>  		goto out_resource;
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index 77767850d0d0..64937baabf93 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -278,6 +278,15 @@ device_initcall(s390_cma_mem_init);
>  
>  #endif /* CONFIG_CMA */
>  
> +struct range arch_get_mappable_range(void)
> +{
> +	struct range memhp_range;
> +
> +	memhp_range.start = 0;
> +	memhp_range.end =  VMEM_MAX_PHYS;
> +	return memhp_range;
> +}
> +
>  int arch_add_memory(int nid, u64 start, u64 size,
>  		    struct mhp_params *params)
>  {
> @@ -291,6 +300,7 @@ int arch_add_memory(int nid, u64 start, u64 size,
>  	if (WARN_ON_ONCE(params->pgprot.pgprot != PAGE_KERNEL.pgprot))
>  		return -EINVAL;
>  
> +	VM_BUG_ON(!memhp_range_allowed(start, size, 1));
>  	rc = vmem_add_mapping(start, size);
>  	if (rc)
>  		return rc;
> diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
> index b239f2ba93b0..749eab43aa93 100644
> --- a/arch/s390/mm/vmem.c
> +++ b/arch/s390/mm/vmem.c
> @@ -536,10 +536,6 @@ int vmem_add_mapping(unsigned long start, unsigned long size)
>  {
>  	int ret;
>  
> -	if (start + size > VMEM_MAX_PHYS ||
> -	    start + size < start)
> -		return -ERANGE;
> -

Is there a reason why you added the memhp_range_allowed() check call
to arch_add_memory() instead of vmem_add_mapping()? If you would do
that, then the extra code in __segment_load() wouldn't be
required.
Even though the error message from memhp_range_allowed() might be
highly confusing.