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xen-devel
Re: [Xen-devel] 2.6.32 PV Xen donU guest panic on nested call to arch_en
Jeremy,
Is it possible for an ongoing lazy mode update to have batched some
MMU updates; an interrupt occurs; an interrupt routine does a non-lazy
MMU update for a PTE that is also in the lazy update queue; that update
is overwritten on return from the interrupt when the update queue is
flushed? Or are the PTE updates protected by a lock? If they are,
wouldn't we deadlock in the interrupt routine when it tries to obtain
that (I assume) spinlock?
Chuck
Jeremy Fitzhardinge wrote:
Disabling interrupts would cause too much latency. I think we may have
done this at one point, but it is very antisocial.
Since lazy mode is effectively disabled in interrupt handlers anyway, it
should just be enough to ignore enter/leave requests. Does this work
for you?
From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
Date: Wed, 8 Dec 2010 14:21:16 -0800
Subject: [PATCH] x86/paravirt: don't enter/leave lazy mode in interrupts.
We already ignore the current state of lazy mode in interrupts, but we
should also ignore any attempt to enter/leave lazy mode within
an interrupt context.
enter_lazy() will BUG if it sees an attempt at a nested entry to lazy
mode, which is generally an error. However, it's possible that an
interrupt handler may do something that would trigger a batched MMU
update, for example, and that could interrupt an existing batched update.
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