Re: [PATCH v3 24/35] OvmfPkg/XenPlatformPei: Rework memory detection

["Anthony PERARD" <anthony.perard@citrix.com>]

On Thu, Jul 25, 2019 at 11:08:29AM +0200, Roger Pau Monné wrote:
> On Wed, Jul 24, 2019 at 05:17:59PM +0100, Anthony PERARD wrote:
> > On Tue, Jul 23, 2019 at 11:42:07AM +0200, Roger Pau Monné wrote:
> > > On Mon, Jul 22, 2019 at 03:53:19PM +0100, Anthony PERARD wrote:
> > > > On Mon, Jul 15, 2019 at 04:15:21PM +0200, Roger Pau Monné wrote:
> > > > > On Thu, Jul 04, 2019 at 03:42:22PM +0100, Anthony PERARD wrote:
> > > > > > +      // error message: CpuDxe: IntersectMemoryDescriptor:
> > > > > > +      //        desc [FC000000, 100000000) type 1 cap 8700000000026001
> > > > > > +      //        conflicts with aperture [FEE00000, FEE01000) cap 1
> > > > > >        //
> > > > > > -      if (Entry->Type != EfiAcpiAddressRangeMemory) {
> > > > > > -        continue;
> > > > > > +      if (!XenHvmloaderDetected ()) {
> > > > > > +        AddReservedMemoryBaseSizeHob (Base, End - Base, FALSE);
> > > > > 
> > > > > This special casing for PVH looks weird, ideally we would like to use
> > > > > the same code path, or else it should be explicitly mentioned why PVH
> > > > > has diverging behaviour.
> > > > 
> > > > I think hvmloader is the issue rather than PVH. Here is part of the
> > > > "memory map" as found in hvmloader/config.h:
> > > > 
> > > >   /* Special BIOS mappings, etc. are allocated from here upwards... */
> > > >   #define RESERVED_MEMBASE              0xFC000000
> > > >   /* NB. ACPI_INFO_PHYSICAL_ADDRESS *MUST* match definition in acpi/dsdt.asl! */
> > > >   #define ACPI_INFO_PHYSICAL_ADDRESS    0xFC000000
> > > >   #define RESERVED_MEMORY_DYNAMIC_START 0xFC001000
> > > >   #define RESERVED_MEMORY_DYNAMIC_END   0xFE000000
> > > > 
> > > > and hvmloader simply creates a single e820 reserved entry, from
> > > > RESERVED_MEMBASE to the top of 4GB. It's probably too much.
> > > 
> > > But isn't this kind of dangerous? How can you assure future versions
> > > of hvmloader won't use this space?
> > > 
> > > > If hvmloader only reserved
> > > > ACPI_INFO_PHYSICAL_ADDRESS-RESERVED_MEMORY_DYNAMIC_END, I might not have
> > > > to special case hvmloader.
> > > 
> > > Could we look into getting this fixed in hvmloader then?
> > > 
> > > I think it's dangerous for OVMF to play such tricks with the memory
> > > map.
> > > 
> > > > As far as I know 0xfee00000 isn't a special
> > > > bios mapping, but something the hardware provides.
> > > 
> > > Yes, that's used by the lapic, so it's not specific to hvmloader.
> > 
> > Right, I've got a closer look at that CpuDxe module, it wants the local
> > APIC memory mapped space to be "mapped IO", and that different than
> > "reserved".
> > 
> > So while parsing the e820 from hvmloader, instead of ignoring all
> > reserved region, I'm going to avoid adding the local apic memory mapped
> > space.
> > 
> > something like:
> >   if (hvmloaderDetected())
> 
> I don't think you need to gate this on hvmloader being used, while
> it's true that PVH memory map doesn't contain such reserved memory
> region ATM I don't see any harm in doing this for PVH also.

Ok.

> >     Base = $(start of the e820 entry);
> >     End = $(start of the e820 entry + size);
> >     LocalApic = 0xfee00000;
> >     if (Base < LocalApic && LocalApic < End) {
> >       AddReservedMemoryRangeHob (Base, LocalApic, FALSE);
> >       if (End > (LocalApic + SIZE_4KB)) {
> 
> The range is actually from 0xfee00000 to 0xfeefffff (2MB), so you
> likely want to make sure non of this is added as reserved?

You mean 1MB, right ? :-). I've try to find out in the Intel manual why
it would be 1MB and couldn't find that, but on the other hand the
initialisation code for OVMF running on QEMU does also reserve 1MB for
the local apic. So I'll change to 1MB.

Thanks,

-- 
Anthony PERARD