linux-kernel - Re: [PATCH 2/6] mm: Add vm_insert_pfn

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Message-Id: <20151211143300.0ac516fbd219a67954698f9a@linux-foundation.org>
Date:	Fri, 11 Dec 2015 14:33:00 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 2/6] mm: Add vm_insert_pfn_prot

On Thu, 10 Dec 2015 19:21:43 -0800 Andy Lutomirski <luto@...nel.org> wrote:

> The x86 vvar mapping contains pages with differing cacheability
> flags.  This is currently only supported using (io_)remap_pfn_range,
> but those functions can't be used inside page faults.

Foggy.  What does "support" mean here?

> Add vm_insert_pfn_prot to support varying cacheability within the
> same non-COW VMA in a more sane manner.

Here, "support" presumably means "insertion of pfns".  Can we spell all
this out more completely please?

> x86 needs this to avoid a CRIU-breaking and memory-wasting explosion
> of VMAs when supporting userspace access to the HPET.
> 

OtherwiseAck.
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