netdev - Re: [PATCH v2 net-next 6/6] net: thunderbolt: Use kmap_local_page() instead of kmap

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Message-ID: <Y386u4X14LYBlX18@black.fi.intel.com>
Date:   Thu, 24 Nov 2022 11:34:51 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Anirudh Venkataramanan <anirudh.venkataramanan@...el.com>
Cc:     netdev@...r.kernel.org, Ira Weiny <ira.weiny@...el.com>,
        "Fabio M . De Francesco" <fmdefrancesco@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>
Subject: Re: [PATCH v2 net-next 6/6] net: thunderbolt: Use kmap_local_page()
 instead of kmap_atomic()

On Wed, Nov 23, 2022 at 12:52:19PM -0800, Anirudh Venkataramanan wrote:
> kmap_atomic() is being deprecated in favor of kmap_local_page(). Replace
> kmap_atomic() and kunmap_atomic() with kmap_local_page() and kunmap_local()
> respectively.
> 
> Note that kmap_atomic() disables preemption and page-fault processing, but
> kmap_local_page() doesn't. When converting uses of kmap_atomic(), one has
> to check if the code being executed between the map/unmap implicitly
> depends on page-faults and/or preemption being disabled. If yes, then code
> to disable page-faults and/or preemption should also be added for
> functional correctness. That however doesn't appear to be the case here,
> so just kmap_local_page() is used.
> 
> Also note that the page being mapped is not allocated by the driver, and so
> the driver doesn't know if the page is in normal memory. This is the reason
> kmap_local_page() is used as opposed to page_address().
> 
> I don't have hardware, so this change has only been compile tested.
> 
> Cc: Michael Jamet <michael.jamet@...el.com>
> Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>

Acked-by: Mika Westerberg <mika.westerberg@...ux.intel.com>