Re: [PATCH v2 5/7] x86, mm: Support huge KVA mappings on x86

From: Toshi Kani
Date: Tue Feb 10 2015 - 15:42:53 EST

On Tue, 2015-02-10 at 10:59 -0800, Dave Hansen wrote:
> On 02/09/2015 02:45 PM, Toshi Kani wrote:
> > Implement huge KVA mapping interfaces on x86. Select
> > HAVE_ARCH_HUGE_VMAP when X86_64 or X86_32 with X86_PAE is set.
> > Without X86_PAE set, the X86_32 kernel has the 2-level page
> > tables and cannot provide the huge KVA mappings.
> Not that it's a big deal, but what's the limitation with the 2-level
> page tables on 32-bit? We have a 4MB large page size available there
> and we already use it for the kernel linear mapping.

ioremap() calls arch-neutral ioremap_page_range() to set up I/O mappings
with PTEs. This patch-set enables ioremap_page_range() to set up PUD &
PMD mappings. With 2-level page table, I do not think this PUD/PMD
mapping code works unless we add some special code.


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