linux-kernel - Re: [PATCH v2 9/9] drm/i915: Use kmap_local_page() in gem/i915_gem

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Message-ID: <ZDPSHYn02GWTSMG4@liuzhao-OptiPlex-7080>
Date:   Mon, 10 Apr 2023 17:08:45 +0800
From:   Zhao Liu <zhao1.liu@...ux.intel.com>
To:     Thomas Hellstr�m 
        <thomas.hellstrom@...ux.intel.com>,
        Matthew Auld <matthew.auld@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
Cc:     Ira Weiny <ira.weiny@...el.com>,
        "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Nirmoy Das <nirmoy.das@...el.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Christian K�nig <christian.koenig@....com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Zhenyu Wang <zhenyu.z.wang@...el.com>,
        Zhao Liu <zhao1.liu@...el.com>
Subject: Re: [PATCH v2 9/9] drm/i915: Use kmap_local_page() in
 gem/i915_gem_execbuffer.c

Thanks all for your review!

On Fri, Mar 31, 2023 at 05:32:17PM +0200, Fabio M. De Francesco wrote:
> Date: Fri, 31 Mar 2023 17:32:17 +0200
> From: "Fabio M. De Francesco" <fmdefrancesco@...il.com>
> Subject: Re: [PATCH v2 9/9] drm/i915: Use kmap_local_page() in
>  gem/i915_gem_execbuffer.c
> 
> On venerd? 31 marzo 2023 13:30:20 CEST Tvrtko Ursulin wrote:
> > On 31/03/2023 05:18, Ira Weiny wrote:
> 

[snip]

>  
> > However I am unsure if disabling pagefaulting is needed or not. Thomas,
> > Matt, being the last to touch this area, perhaps you could have a look?
> > Because I notice we have a fallback iomap path which still uses
> > io_mapping_map_atomic_wc. So if kmap_atomic to kmap_local conversion is
> > safe, does the iomap side also needs converting to
> > io_mapping_map_local_wc? Or they have separate requirements?
> 
> AFAIK, the requirements for io_mapping_map_local_wc() are the same as for 
> kmap_local_page(): the kernel virtual address is _only_ valid in the caller 
> context, and map/unmap nesting must be done in stack-based ordering (LIFO).
> 
> I think a follow up patch could safely switch to io_mapping_map_local_wc() / 
> io_mapping_unmap_local_wc since the address is local to context.
> 
> However, not being an expert, reading your note now I suspect that I'm missing 
> something. Can I ask why you think that page-faults disabling might be 
> necessary? 


About the disabling of pagefault here, could you please talk more about
it? :-)

>From previous discussions and commit history, I didn't find relevant
information and I lack background knowledge about it...

If we have the reason to diable pagefault, I will fix and refresh the new
version.

Thanks,
Zhao

> 
> Thanks,
> 
> Fabio
> 
> > Regards,
> > 
> > Tvrtko
> 
> 
>