Re: [Xen-devel] [PATCHv2] x86: map portion of kexec crash area that is within the direct map area

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Thu, Jan 09, 2014 at 11:15:04PM +0000, Andrew Cooper wrote:
> On 09/01/2014 19:50, Daniel Kiper wrote:
> > By the way, why map_domain_page() behavior depends on debug option?
> > It is not nice because we could be trapped by this in the future in
> > more serious places. Could map_domain_page() work in the same way
> > with or without debug option?
>
> With a debug build of Xen, map_domain_page() always mutates the
> pagetables and hands out virtual addresses from the mapcache region.
> This is to test map_domain_page() itself, as well as making domain
> mapping leaks more obvious (as the mapcache is under heavier load).
>
> For a non-debug build of Xen, any map_domain_page() calls which can be
> satisfied by returning a virtual address from the direct map region
> (i.e. for pages below the 5TiB boundary which is basically all of them
> unless you have more money than sense) are, which avoided excessive use
> of the mapcache, and avoids a TLB shootdown/flush on unmap.

Make sens. Thanks for explanation.

Daniel

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