Re: Page Attribute Table (PAT) support?

[Timur Tabi <ttabi@interactivesi.com>]

** Reply to message from Jeff Hartmann <jhartmann@valinux.com> on Wed, 24 Jan
2001 13:41:41 -0700

> When you mark a page UCWC, you better 
> have removed all cached mappings or your asking for REAL trouble.

What exactly do you mean by "removed all cached mappings"?  Does that mean that
if one virtual address is a UCWC mapping of a physical page, then ALL virtual
addresses mapped to that page must also be UCWC?

In my driver, I use ioremap_nocache() on physical memory (real RAM) to create
an uncached "alias" (a virtual address) to a physical page of RAM.  When I
access the memory via this virtual address, the memory access is not cached.
What I reall need is to be able to also have that virtual address as Write
Combined.

Since all physical RAM is mapped as cached via the kernel (on a 1-to-1 basis),
and since there can be several other virtual addresses that point to that memory
(e.g. user virtual address), I can't see how these virtual addresses can be
removed.


-- 
Timur Tabi - ttabi@interactivesi.com
Interactive Silicon - http://www.interactivesi.com

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