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SubjectRe: issue with patch "x86: no CPA on iounmap"
Siddha, Suresh B wrote:
> This is wrt to x86 git commit f56d005d30342a45d8af2b75ecccc82200f09600
> "x86: no CPA on iounmap"
> This can use performance issue. When a GART driver unmaps a RAM page,
> which was mapped as UC, this commit will still retain UC attribute
> on the kernel identity mapping. This can cause mysterious performance issue
> if this freed page gets used by kernel later.
> For now we should change the attribute during iounmap and in future PAT
> infrastructure will have necessary hooks to avoid the aliasing issues.

this is a hard one; because the flipside is someone ioremapping the same page twice
(which is not impossible if there's 2 1k bars)... and then one of them gets iounmapped,
which would turn the page cachable again.

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