linux-kernel - Re: [PATCH v3 15/15] nvme: Ensure atomic writes will be executed atomically

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Message-ID: <22b297b5-99ec-4b75-b81a-6b603d1efef2@nvidia.com>
Date: Fri, 26 Jan 2024 03:50:54 +0000
From: Chaitanya Kulkarni <chaitanyak@...dia.com>
To: Keith Busch <kbusch@...nel.org>, John Garry <john.g.garry@...cle.com>
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	<bvanassche@....org>, Alan Adamson <alan.adamson@...cle.com>
Subject: Re: [PATCH v3 15/15] nvme: Ensure atomic writes will be executed
 atomically

On 1/24/2024 4:52 PM, Keith Busch wrote:
> On Wed, Jan 24, 2024 at 11:38:41AM +0000, John Garry wrote:
>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
>> index 5045c84f2516..6a34a5d92088 100644
>> --- a/drivers/nvme/host/core.c
>> +++ b/drivers/nvme/host/core.c
>> @@ -911,6 +911,32 @@ static inline blk_status_t nvme_setup_rw(struct nvme_ns *ns,
>>   	if (req->cmd_flags & REQ_RAHEAD)
>>   		dsmgmt |= NVME_RW_DSM_FREQ_PREFETCH;
>>   
>> +	/*
>> +	 * Ensure that nothing has been sent which cannot be executed
>> +	 * atomically.
>> +	 */
>> +	if (req->cmd_flags & REQ_ATOMIC) {
>> +		struct nvme_ns_head *head = ns->head;
>> +		u32 boundary_bytes = head->atomic_boundary;
>> +
>> +		if (blk_rq_bytes(req) > ns->head->atomic_max)
>> +			return BLK_STS_IOERR;
>> +
>> +		if (boundary_bytes) {
>> +			u32 mask = boundary_bytes - 1, imask = ~mask;
>> +			u32 start = blk_rq_pos(req) << SECTOR_SHIFT;
>> +			u32 end = start + blk_rq_bytes(req);
>> +
>> +			if (blk_rq_bytes(req) > boundary_bytes)
>> +				return BLK_STS_IOERR;
>> +
>> +			if (((start & imask) != (end & imask)) &&
>> +			    (end & mask)) {
>> +				return BLK_STS_IOERR;
>> +			}
>> +		}
>> +	}
> 
> Aren't these new fields, atomic_max and atomic_boundary, duplicates of
> the equivalent queue limits? Let's just use the queue limits instead.
> 
> And couldn't we generically validate the constraints are not violated in
> submit_bio_noacct() instead of doing that in the low level driver? The
> driver assumes all other requests are already sanity checked, so I don't
> think we should change the responsibility for that just for this flag.
> 

does it makes sense to move about code to the helper ? perhaps inline ?

-ck