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Re: [Xen-devel] __HYPERVISOR_COMPAT_VIRT_START for HVM guest with PV dri

To: Chuck Anderson <chuck.anderson@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] __HYPERVISOR_COMPAT_VIRT_START for HVM guest with PV drivers
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 20 Aug 2009 17:27:12 +0100
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On 20/08/2009 16:30, "Chuck Anderson" <chuck.anderson@xxxxxxxxxx> wrote:

> Do the guest virtual addresses passed by a hypervisor call on a 32-bit
> HVM with PV drivers guest to a 64-bit hypervisor need to lie below
> __HYPERVISOR_COMPAT_VIRT_START?  Both HVM and PVM domains have their
> hv_compat_vstart set to __HYPERVISOR_COMPAT_VIRT_START.  The
> hypervisor's compat layer is causing the balloon driver's
> HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation)
> hypervisor call to error out in xen/common/compat/memory.c
> compat_memory_op(), compat_handle_ok(), because the PVHVM guest's
> extent_start lies above __HYPERVISOR_COMPAT_VIRT_START.  The following
> patch appears to fix the problem but I want to make sure it is fixing
> the real bug:

Yeah, you pretty much have it figured. I may just clean up for style (I
think an extra macro for this is a bit pointless), but the patch is
fundamentally good.


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