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xen-devel
Re: [Xen-devel] a quick question about _PAGE_GLOBAL flag in para virt mo
On Sun, Feb 15, 2009 at 02:26:13PM -0800, Jeremy Fitzhardinge wrote:
> >why not set global bit for user kernel pages? I guess this is because
> >when domain switchs, all tlb entries will still be flushed, so it's
> >not necessary for user kernel pages. Is my understanding right?
>
> 64-bit Xen uses paging to protect the guest kernel from guest usermode,
> and protect Xen from the guest kernel, and as a result has to do a cr3
> reload for any user->kernel switch (which is why it has to go via Xen).
> We don't want kernel mappings to be visible to usermode, so they have to
> only be in tlb while we're actually running in guest kernel mode;
And here's a real example of what happens when you don't get this right:
http://blogs.sun.com/levon/entry/xen_compatibility_with_solaris
regards
john
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