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

Joerg Roedel
2010-04-27T13:57:16Z

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