Re: fwupd support under Xen - firmware updates with the UEFI capsule

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.07.2020 23:01, Andrew Cooper wrote:
> On 28/07/2020 21:00, Jan Beulich wrote:
> > On 28.07.2020 09:41, Norbert Kaminski wrote:
> > > I'm trying to add support for the firmware updates with the UEFI
> > > capsule in
> > > Qubes OS. I've got the troubles with reading ESRT (EFI System
> > > Resource Table)
> > > in the dom0, which is based on the EFI memory map. The EFI_MEMMAP is not
> > > enabled despite the loaded drivers (CONFIG_EFI, CONFIG_EFI_ESRT) and
> > > kernel
> > > cmdline parameters (add_efi_memmap):
> > >
> > > ```
> > > [    3.451249] efi: EFI_MEMMAP is not enabled.
> > > ```
> > It is, according to my understanding, a layering violation to expose
> > the EFI memory map to Dom0. It's not supposed to make use of this
> > information in any way. Hence any functionality depending on its use
> > also needs to be implemented in the hypervisor, with Dom0 making a
> > suitable hypercall to access this functionality. (And I find it
> > quite natural to expect that Xen gets involved in an update of the
> > firmware of a system.)
> ERST is a table (read only by the looks of things) which is a catalogue
> of various bits of firmware in the system, including GUIDs for
> identification, and version information.
>
> It is the kind of data which the hardware domain should have access to,
> and AFAICT, behaves just like a static ACPI table.
I'm unaware of us hiding this table, so Dom0 has access.

> Presumably it wants to an E820 reserved region so dom0 gets indent
> access, and something in the EFI subsystem needs extending to pass the
> ERST address to dom0.
I'm afraid the beginning of this sentence is such that I can't guess
what exactly you mean. As per above - I don't see why Dom0 wouldn't
have access to ERST. What it doesn't (and shouldn't) have access to is
the raw EFI memory map (there's no E820 map there). There is a way
for Dom0 to get at some "cooked" memory map (XENMEM_machine_memory_map),
but of course in a r/o fashion only.

Jan