Re: [Xen-devel] [PATCH] linux/i386: allow CONFIG_HIGHPTE on i386

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 10/1/07 11:14, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

>> Is it actually safe to circumvent tlb_remove_page()? It does rather more
>> than just free_page()! That's why I used a ForeignPage hook when writing the
>> i386 code. It's certainly *not* safe to assume that whoever wrote that part
>> of the x86/64 port understood all the ramifications of what they were doing.
> 
> Not really, as I understand it - it either frees the page (when the TLB is in
> fast
> mode) or inserts the page into the gather list, bumping the contained pages
> count and freeing all of them and flushing the hardware TLBs if exceeding the
> threshold - the latter step is otherwise done from tlb_finish_mmu().

Presumably this gathering happens because it may not be safe to free the
pages without having first flushed the TLBs? Freeing the page with no TLB
flush management at all would be a bad idea in that case.

And I said that sync'ing with i386 is a good general rule. I trust the code
a lot more. :-)

 -- Keir


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