Re: [PATCH 2/6] mm: Add vm_insert_pfn_prot

From: Andrew Morton
Date: Fri Dec 11 2015 - 17:33:08 EST

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

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