linux-kernel - Re: [PATCH v4 03/23] PCI/P2PDMA: Attempt to set map

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Date:   Mon, 13 Dec 2021 22:00:27 +0000
From:   Chaitanya Kulkarni <chaitanyak@...dia.com>
To:     Logan Gunthorpe <logang@...tatee.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
CC:     Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian König <christian.koenig@....com>,
        John Hubbard <jhubbard@...dia.com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jakowski Andrzej <andrzej.jakowski@...el.com>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        Martin Oliveira <martin.oliveira@...eticom.com>,
        Chaitanya Kulkarni <ckulkarnilinux@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v4 03/23] PCI/P2PDMA: Attempt to set map_type if it has
 not been set

On 11/17/21 1:53 PM, Logan Gunthorpe wrote:
> Attempt to find the mapping type for P2PDMA pages on the first
> DMA map attempt if it has not been done ahead of time.
> 
> Previously, the mapping type was expected to be calculated ahead of
> time, but if pages are to come from userspace then there's no
> way to ensure the path was checked ahead of time.
> 
> This change will calculate the mapping type if it hasn't pre-calculated
> so it is no longer invalid to call pci_p2pdma_map_sg() before the mapping
> type is calculated, so drop the WARN_ON when that is he case.
> 
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---

Perhaps a comment would be nice in the default case in
pci_p2pdma_map_sg_attrs() where you have removed the WARN_ON_ONCE().

Either way, looks good.

Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>