Re: 2.6.33-rc2: Xen/Guest switching to user mode with no user pagetables

From: Ian Campbell
Date: Fri Jan 15 2010 - 06:30:02 EST

On Fri, 2010-01-15 at 00:36 -0800, Christian Kujau wrote:
> On Sun, 10 Jan 2010 at 12:59, Ian Campbell wrote:
> > The correct fix is for the Xen backend to declare kernel RPL == 0 for 64
> > bit guests -- the hyervisor already takes care of all the necessary
> > squashing to ring 3 transparently (because making the guest worry about
> > it would break the very common assumption that you can distinguish user
> > from kernel CS by RPL).
> Yes' it's a 64bit guest, I should have mentioned this from the beginning.

That's OK, I already knew because only 64 bit guests have a separate
user page table.

> With the 2 patches from Ian and Cyrill applied, the DomU is now booting
> fine again (currently running mainline -git).

Excellent. These patches are both now in -tip. They are in the urgent
branch so I assume they will be heading to mainline before too long.

> Cyrill: with your patch alone (for arch/x86/kernel/process.c), the DomU
> is still not booting, Dom0 "xm dmesg" reporting the same error. As it's
> working with both patches applied, should I try to test with only Ian's
> patch (for arch/x86/xen/enlighten.c) applied?

It's OK, both patches are definitely required to fix 64 bit guests so
there is no point in testing just one or the other.


Ian Campbell
Current Noise: Exodus - Scar Spangled Banner

War is much too serious a matter to be entrusted to the military.
-- Clemenceau

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