Re: [PATCH] nvmet: fix the use of ZERO_PAGE in nvme_execute_identify_ns_nvm()

[Nilay Shroff <nilay@linux.ibm.com>]

On 11/22/24 21:30, Keith Busch wrote:
> On Fri, Nov 22, 2024 at 01:08:28PM +0100, Christoph Hellwig wrote:
>> On Fri, Nov 22, 2024 at 02:20:36PM +0530, Nilay Shroff wrote:
>>> The nvme_execute_identify_ns_nvm function uses ZERO_PAGE
>>> for copying SG list with all zeros. As ZERO_PAGE would not
>>> necessarily return the virtual-address of the zero page, we
>>> need to first convert the page address to kernel virtual-
>>> address and then use it as source address for copying the
>>> data to SG list with all zeros.
>>>
>>> Using return address of ZERO_PAGE(0) as source address for
>>> copying data to SG list would fill the target buffer with
>>> random value and causes the undesired side effect. This patch
>>> implements the fix ensuring that we use virtual-address of the
>>> zero page for copying all zeros to the SG list buffers.
>>
>> I wonder if using ZERO_PAGE() is simply a little too smart for it's
>> own sake and it should just use kzalloc like a bunch of other identify
>> implementation..
> 
> Sure. That'll make it easier to report non-zero values if we decide to
> implement a non-stubbed version of this identification later.

Ok, so if we prefer using kzalloc instead of ZERO_PAGE() in 
nvme_execute_identify_ns_nvm function, as we're using kzalloc 
at other identify call sites, then I would update the patch 
and send v2 where we would replace ZERO_PAGE() with kzalloc. 

Thanks,
--Nilay