linux-kernel - Re: [PATCH 16/22] KVM: MMU: Track page fault data in struct vcpu

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Message-ID: <20100427135700.GK11097@amd.com>
Date:	Tue, 27 Apr 2010 15:57:00 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/22] KVM: MMU: Track page fault data in struct vcpu

On Tue, Apr 27, 2010 at 04:37:42PM +0300, Avi Kivity wrote:
> On 04/27/2010 04:28 PM, Joerg Roedel wrote:
> >
> >>>diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> >>>index d9dfc8c..8426870 100644
> >>>--- a/arch/x86/include/asm/kvm_host.h
> >>>+++ b/arch/x86/include/asm/kvm_host.h
> >>>@@ -298,6 +298,9 @@ struct kvm_vcpu_arch {
> >>>  	/* Used for two dimensional paging emulation */
> >>>  	struct kvm_mmu nested_mmu;
> >>>
> >>>+	unsigned long fault_address;
> >>Probably a problem on i386.  How does npt handle faults when the
> >>guest is using pae paging and the host (in our case the guest...)
> >>isn't?  I see it uses exit_info_2 for the address, which is a u64.
> >This shouldn't be an issue. If we run on 32bit host with nested paging
> >the guest can't have more than 4gb of addressable memory because of the
> >page table limitations (nested page table is always in host format).
> 
> But the nested guest can use pae paging and generate a #NPF with
> exit_info_2 > 4GB.  So we need to keep the full fault address; if we
> truncate, the guest might actually resolve the fault and let the
> nested guest continue.

This could only be a malicious guest because it can't have memory above
4gb. But a guest could certainly setup its page tables to point there,
thats true. So I change it to u64.

	Joerg


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