Re: [edk2-devel] [PATCH v4 3/5] OvmfPkg/PlatformInitLib: Add PlatformAddHobCB

["Gerd Hoffmann" <kraxel@redhat.com>]

On Tue, Jan 24, 2023 at 04:33:48PM -0600, Tom Lendacky wrote:
> On 1/17/23 06:16, Gerd Hoffmann via groups.io wrote:
> > Add PlatformAddHobCB() callback function for use with
> > PlatformScanE820().  It adds HOBs for high memory and reservations (low
> > memory is handled elsewhere because there are some special cases to
> > consider).  This replaces calls to PlatformScanOrAdd64BitE820Ram() with
> > AddHighHobs = TRUE.
> > 
> > Write any actions done (adding HOBs, skip unknown types) to the firmware
> > log with INFO loglevel.
> > 
> > Also remove PlatformScanOrAdd64BitE820Ram() which is not used any more.
> 
> Hi Gerd,
> 
> A problem was reported to me for an SEV-ES guest that I bisected to this
> patch. It only occurs when using the OVMF_CODE.fd file without specifying
> the OVMF_VARS.fd file (i.e. only the one pflash device on the qemu command
> line, but not using the OVMF.fd file). I don't ever boot without an
> OVMF_VARS.fd file, so I didn't catch this.
> 
> With this patch, SEV-ES terminates now because it detects doing MMIO to
> encrypted memory area at 0xFFC00000 (where the OVMF_VARS.fd file would
> normally be mapped). Prior to this commit, an SEV-ES guest booted without
> issue in this configuration.
> 
> First, is not specifying an OVMF_VARS.fd a valid configuration for booting
> given the CODE/VARS split build?

No.

> If it is valid, is the lack of the OVMF_VARS.fd resulting in the 0xFFC00000
> address range getting marked reserved now (and thus mapped encrypted)?

I have no clue offhand.  The patch is not supposed to change OVMF
behavior.  Adding the HOBs was done by the (increasingly messy)
PlatformScanOrAdd64BitE820Ram() function before, with this patch in
place PlatformScanE820() + PlatformAddHobCB() handle it instead.  The
end result should be identical though.

OVMF does MMIO access @ 0xFFC00000, to check whenever it finds flash
there or not (to handle the -bios OVMF.fd case).  That happens at a
completely different place though (see
OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c).

> Let me know if you need me to provide any output or testing if you can't
> boot an SEV-ES guest.

Yes, the firmware log hopefully gives clues what is going on here.

thanks,
  Gerd