On 10.12.20 09:58, Anshuman Khandual wrote:
>
>
> On 12/10/20 1:32 PM, David Hildenbrand wrote:
>> On 10.12.20 08:40, Anshuman Khandual wrote:
>>>
>>>
>>> On 12/10/20 12:34 PM, David Hildenbrand wrote:
>>>>
>>>>> Am 10.12.2020 um 07:58 schrieb Heiko Carstens <hca@xxxxxxxxxxxxx>:
>>>>>
>>>>> 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@xxxxxxxxxxxxx>
>>>>>
>>>>> 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@xxxxxxxxxx>
>>>>> */
>>>>>
>>>>> +#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).
>>> Didn't quite understand "Not sure if we really need new checks in common code".
>>> Could you please be more specific. New checks as in pagemap_range() ? Because
>>> other places it is either replacing erstwhile check_hotplug_memory_addressable()
>>> or just moving existing checks from platform arch_add_memory() to the beginning
>>> of various hotplug paths.
>>
>> The main concern I have with current code is that it makes it impossible
>> for some driver to detect which ranges it could actually later hotplug.
>> You cannot warn about a strange setup before you actually run into the
>> issues while trying to add memory. Like returning "-EINVAL" from a
>> function but not exposing which values are actually valid.
>>
>> If we have memhp_get_pluggable_range(), we have such a mechanism and
>>
>> 1. Trying to add out-of-range memory will fail (although deep down in
>> arch code, but at least it fails).
>>
>> 2. There is a way for drivers to find out which values are actually
>> valid before triggering 1.
>
> Right, that is an important use case from a driver perspective as it
> helps validate the range being attempted for hotplug, before failing.
> But then memhp_range_allowed() also uses the same mechanism i.e
> memhp_get_pluggable_range() to unify
>
> 1. Generic check_hotplug_memory_addressable()
> 2. Platform checks in arch_add_memory()
>
> This unified function can be called just at the beginning of memory
> hotplug so that both (1) and (2) can be dropped all together. This
> is just a logical extension which does improve the memory hotplug
> implementation (in itself) by failing earlier and while at it, also
> unifying generic and platform specific range constraints. Both the
> use cases are orthogonal IMHO.
As longs as it simplifies the code sure. But at least in the s390x case,
we cannot get rid of the internal checks.
--
Thanks,
David / dhildenb
