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From: Ira Weiny <ira.weiny@intel.com>
To: "hch@lst.de" <hch@lst.de>
Cc: "yangx.jy@fujitsu.com" <yangx.jy@fujitsu.com>,
	Jason Gunthorpe <jgg@nvidia.com>,
	"lizhijian@fujitsu.com" <lizhijian@fujitsu.com>,
	"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
	"tom@talpey.com" <tom@talpey.com>,
	"yanjun.zhu@linux.dev" <yanjun.zhu@linux.dev>,
	"rpearsonhpe@gmail.com" <rpearsonhpe@gmail.com>,
	"y-goto@fujitsu.com" <y-goto@fujitsu.com>,
	"tomasz.gromadzki@intel.com" <tomasz.gromadzki@intel.com>
Subject: Re: [RFC PATCH v2 2/2] RDMA/rxe: Support RDMA Atomic Write operation
Date: Thu, 27 Jan 2022 10:08:33 -0800	[thread overview]
Message-ID: <20220127180833.GF785175@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20220127095730.GA14946@lst.de>

On Thu, Jan 27, 2022 at 10:57:30AM +0100, Christoph Hellwig wrote:
> On Thu, Jan 27, 2022 at 09:37:59AM +0000, yangx.jy@fujitsu.com wrote:
> > Do you mean we have to consider that some allocated pages come from high 
> > memory?
> >
> > I think INFINIBAND_VIRT_DMA kconfig[1] has ensured that all allocated 
> > pages have a kernel virtual address.
> 
> rxe and siw depend on INFINIBAND_VIRT_DMA which depends on !HIGHMEM,
> so you don't need kmap here at all.

Until/if I get PKS protecting pmem.[1]  Then if the page is pmem, page_address()
will give you an address which you will fault on when you access it.

> 
> > In this case, is it OK to call page_address() directly?
> 
> Yes.

For now yes...  But please use kmap_local_page() and it will do the right thing
(by default call page_address() on !HIGHMEM systems).

IMO page_address() is a hold over from a time when memory management was much
simpler and, again IMO, today its use assumes too much for drivers like this.
As more protections on memory are implemented it presents a series of land
mines to be found.

While kmap is also a hold over I'm trying to redefine it to be 'get the kernel
mapping' rather than 'map this into highmem'...  But perhaps I'm losing that
battle...

Ira

[1] https://lore.kernel.org/lkml/20220127175505.851391-1-ira.weiny@intel.com/T/#mcd60ea9a9c7b90e63b8d333c9270186fc7e47707

  reply	other threads:[~2022-01-27 18:08 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-13  3:03 [RFC PATCH v2 0/2] RDMA/rxe: Add RDMA Atomic Write operation Xiao Yang
2022-01-13  3:03 ` [RFC PATCH v2 1/2] RDMA/rxe: Rename send_atomic_ack() and atomic member of struct resp_res Xiao Yang
2022-01-13  3:03 ` [RFC PATCH v2 2/2] RDMA/rxe: Support RDMA Atomic Write operation Xiao Yang
2022-01-13 11:35   ` kernel test robot
2022-01-13 12:16   ` kernel test robot
2022-01-13 12:16     ` kernel test robot
2022-01-17 13:16   ` Jason Gunthorpe
2022-01-18  8:01     ` yangx.jy
2022-01-18 12:35       ` Jason Gunthorpe
2022-01-19  1:54         ` lizhijian
2022-01-19 12:36           ` Jason Gunthorpe
2022-01-19 16:47             ` Ira Weiny
2022-01-20 12:07             ` Li, Zhijian
2022-01-21 12:58               ` Jason Gunthorpe
2022-01-21 16:06                 ` Ira Weiny
2022-01-21 16:08                   ` Ira Weiny
2022-01-24  3:47                     ` lizhijian
2022-01-27  9:37                   ` yangx.jy
2022-01-27  9:57                     ` hch
2022-01-27 18:08                       ` Ira Weiny [this message]
2022-01-28  6:16                         ` hch
2022-01-28 19:15                           ` Ira Weiny
2022-02-10 11:06                             ` yangx.jy
2022-02-11 18:30                               ` Ira Weiny
2022-01-18  8:02     ` yangx.jy
2022-01-18  8:04     ` yangx.jy
2022-01-18  9:03       ` yangx.jy

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