linux-kernel - Re: [kvm-devel] [PATCH] KVM: MMU: Fix guest writes to nonpae pde

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Date:	Sun, 11 Mar 2007 11:32:50 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...ranet.com>
Cc:	kvm-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [kvm-devel] [PATCH] KVM: MMU: Fix guest writes to nonpae pde


* Avi Kivity <avi@...ranet.com> wrote:

> KVM shadow page tables are always in pae mode, regardless of the guest 
> setting.  This means that a guest pde (mapping 4MB of memory) is 
> mapped to two shadow pdes (mapping 2MB each).
> 
> When the guest writes to a pte or pde, we intercept the write and 
> emulate it. We also remove any shadowed mappings corresponding to the 
> write.  Since the mmu did not account for the doubling in the number 
> of pdes, it removed the wrong entry, resulting in a mismatch between 
> shadow page tables and guest page tables, followed shortly by guest 
> memory corruption.
> 
> This patch fixes the problem by detecting the special case of writing 
> to a non-pae pde and adjusting the address and number of shadow pdes 
> zapped accordingly.
> 
> Signed-off-by: Avi Kivity <avi@...ranet.com>

tested this with both PAE and non-PAE Linux host and guest - works fine.

Acked-by: Ingo Molnar <mingo@...e.hu>

	Ingo
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