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

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Message-Id: <E026809E-4624-4ACE-B309-0443704C637B@redhat.com>
Date:   Thu, 10 Dec 2020 08:04:32 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     Anshuman Khandual <anshuman.khandual@....com>, 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()


> Am 10.12.2020 um 07:58 schrieb Heiko Carstens <hca@...ux.ibm.com>:
> 
> On Thu, Dec 10, 2020 at 09:48:11AM +0530, Anshuman Khandual wrote:
>>>> Alternatively leaving __segment_load() and vmem_add_memory() unchanged
>>>> will create three range checks i.e two memhp_range_allowed() and the
>>>> existing VMEM_MAX_PHYS check in vmem_add_mapping() on all the hotplug
>>>> paths, which is not optimal.
>>> 
>>> Ah, sorry. I didn't follow this discussion too closely. I just thought
>>> my point of view would be clear: let's not have two different ways to
>>> check for the same thing which must be kept in sync.
>>> Therefore I was wondering why this next version is still doing
>>> that. Please find a way to solve this.
>> 
>> The following change is after the current series and should work with
>> and without memory hotplug enabled. There will be just a single place
>> i.e vmem_get_max_addr() to update in case the maximum address changes
>> from VMEM_MAX_PHYS to something else later.
> 
> Still not. That's way too much code churn for what you want to achieve.
> If the s390 specific patch would look like below you can add
> 
> Acked-by: Heiko Carstens <hca@...ux.ibm.com>
> 
> But please make sure that the arch_get_mappable_range() prototype in
> linux/memory_hotplug.h is always visible and does not depend on
> CONFIG_MEMORY_HOTPLUG. I'd like to avoid seeing sparse warnings
> because of this.
> 
> Thanks.
> 
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index 77767850d0d0..e0e78234ae57 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -291,6 +291,7 @@ 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..ccd55e2f97f9 100644
> --- a/arch/s390/mm/vmem.c
> +++ b/arch/s390/mm/vmem.c
> @@ -4,6 +4,7 @@
>  *    Author(s): Heiko Carstens <heiko.carstens@...ibm.com>
>  */
> 
> +#include <linux/memory_hotplug.h>
> #include <linux/memblock.h>
> #include <linux/pfn.h>
> #include <linux/mm.h>
> @@ -532,11 +533,23 @@ void vmem_remove_mapping(unsigned long start, unsigned long size)
>    mutex_unlock(&vmem_mutex);
> }
> 
> +struct range arch_get_mappable_range(void)
> +{
> +    struct range range;
> +
> +    range.start = 0;
> +    range.end = VMEM_MAX_PHYS;
> +    return range;
> +}
> +
> int vmem_add_mapping(unsigned long start, unsigned long size)
> {
> +    struct range range;
>    int ret;
> 
> -    if (start + size > VMEM_MAX_PHYS ||
> +    range = arch_get_mappable_range();
> +    if (start < range.start ||
> +        start + size > range.end ||
>        start + size < start)
>        return -ERANGE;
> 
> 

Right, what I had in mind as reply to v1. Not sure if we really need new checks in common code. Having a new memhp_get_pluggable_range() would be sufficient for my use case (virtio-mem).