Re: [Xen-devel] [PATCH for-4.11] libxl: fix memory map reported to PVH guests

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Apr 20, 2018 at 08:01:35AM -0600, Jan Beulich wrote:
> >>> On 20.04.18 at 15:52, <roger.pau@xxxxxxxxxx> wrote:
> > PVH guests with 4GB of RAM or more get a memory map like the
> > following:
> > 
> > 0x00000000000000 - 0x000000fee00000 RAM
> > 0x000000fee00000 - 0x00000100000000 RESERVED
> > 0x000000fc009000 - 0x000000fc009040 ACPI
> > 0x000000fc000000 - 0x000000fc001000 ACPI
> > 0x000000fc001000 - 0x000000fc009000 ACPI
> > 0x00000100000000 - 0x000001fb200400 RAM
> > 
> > This is wrong because ACPI regions are also reported as RAM regions.
> > The cause of this issue is not setting a big enough MMIO hole, current
> > libxl code only takes into account the address of the local APIC page
> > and the reserved pages in order to set the size of the MMIO hole, when
> > it should also take into account the location of the ACPI tables.
> > 
> > After the fix the layout reported for the same guest is:
> > 
> > 0x00000000000000 - 0x000000fc000000 RAM
> > 0x000000fc000000 - 0x00000100000000 RESERVED
> > 0x000000fc009000 - 0x000000fc009040 ACPI
> > 0x000000fc000000 - 0x000000fc001000 ACPI
> > 0x000000fc001000 - 0x000000fc009000 ACPI
> > 0x00000100000000 - 0x000001fe000400 RAM
> 
> But this is still wrong - no two regions may overlap, regardless of type.

It's going to be more complicated to fix that. I can give it a try,
but I think this is strictly better than what we do now.

Maybe instead of marking the whole MMIO hole as reserved we should
only mark as reserved the lapic page and the special pages? That
should avoid any overlaps.

> Also you appear to be losing all RAM in [fc009000, fee00000).

This is not populated. Note how:

0x000001fe000400 - 0x000001fb200400 == 0x000000fee00000 - 0x000000fc000000

The memory is shifted towards the end.

Thanks, Roger.

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