linux-kernel - Re: [PATCH 1/8] scsi: add a host / host template field for the virt boundary

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Message-ID: <ea0f90cd-6263-6a9e-9c88-ed8a8017317e@acm.org>
Date:   Mon, 17 Jun 2019 13:51:02 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Christoph Hellwig <hch@....de>,
        "Martin K . Petersen" <martin.petersen@...cle.com>
Cc:     Sagi Grimberg <sagi@...mberg.me>, Max Gurtovoy <maxg@...lanox.com>,
        linux-rdma@...r.kernel.org, linux-scsi@...r.kernel.org,
        megaraidlinux.pdl@...adcom.com, MPT-FusionLinux.pdl@...adcom.com,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/8] scsi: add a host / host template field for the virt
 boundary

On 6/17/19 5:19 AM, Christoph Hellwig wrote:
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 65d0a10c76ad..d333bb6b1c59 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1775,7 +1775,8 @@ void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
>   	dma_set_seg_boundary(dev, shost->dma_boundary);
>   
>   	blk_queue_max_segment_size(q, shost->max_segment_size);
> -	dma_set_max_seg_size(dev, shost->max_segment_size);
> +	blk_queue_virt_boundary(q, shost->virt_boundary_mask);
> +	dma_set_max_seg_size(dev, queue_max_segment_size(q));

Although this looks fine to me for LLDs that own a PCIe device, I doubt 
this is correct for SCSI LLDs that share a PCIe device with other ULP 
drivers. From the RDMA core:

	/* Setup default max segment size for all IB devices */
	dma_set_max_seg_size(device->dma_device, SZ_2G);

Will instantiating a SCSI host (iSER or SRP) for an RDMA adapter cause 
the maximum segment size to be modified for all ULP drivers associated 
with that HCA?

Thanks,

Bart.