Various problems trying to vga-passthrough a Renoir iGPU to a xen/qubes-os hvm

Wed Dec 22 14:07:24 UTC 2021

On Tue, Dec 21, 2021 at 6:09 PM Yann Dirson <ydirson at free.fr> wrote:
>
>
>
> ----- Mail original -----
> > De: "Alex Deucher" <alexdeucher at gmail.com>
> > À: "Yann Dirson" <ydirson at free.fr>
> > Cc: "Christian König" <ckoenig.leichtzumerken at gmail.com>, "amd-gfx list" <amd-gfx at lists.freedesktop.org>
> > Envoyé: Mardi 21 Décembre 2021 23:31:01
> > Objet: Re: Various problems trying to vga-passthrough a Renoir iGPU to a xen/qubes-os hvm
> >
> > On Tue, Dec 21, 2021 at 5:12 PM Yann Dirson <ydirson at free.fr> wrote:
> > >
> > >
> > > Alex wrote:
> > > >
> > > > On Sun, Dec 19, 2021 at 11:41 AM Yann Dirson <ydirson at free.fr>
> > > > wrote:
> > > > >
> > > > > Christian wrote:
> > > > > > Am 19.12.21 um 17:00 schrieb Yann Dirson:
> > > > > > > Alex wrote:
> > > > > > >> Thinking about this more, I think the problem might be
> > > > > > >> related
> > > > > > >> to
> > > > > > >> CPU
> > > > > > >> access to "VRAM".  APUs don't have dedicated VRAM, they
> > > > > > >> use a
> > > > > > >> reserved
> > > > > > >> carve out region at the top of system memory.  For CPU
> > > > > > >> access
> > > > > > >> to
> > > > > > >> this
> > > > > > >> memory, we kmap the physical address of the carve out
> > > > > > >> region
> > > > > > >> of
> > > > > > >> system
> > > > > > >> memory.  You'll need to make sure that region is
> > > > > > >> accessible to
> > > > > > >> the
> > > > > > >> guest.
> > > > > > > So basically, the non-virt flow is is: (video?) BIOS
> > > > > > > reserves
> > > > > > > memory, marks it
> > > > > > > as reserved in e820, stores the physaddr somewhere, which
> > > > > > > the
> > > > > > > GPU
> > > > > > > driver gets.
> > > > > > > Since I suppose this includes the framebuffer, this
> > > > > > > probably
> > > > > > > has to
> > > > > > > occur around
> > > > > > > the moment the driver calls
> > > > > > > drm_aperture_remove_conflicting_pci_framebuffers()
> > > > > > > (which happens before this hw init step), right ?
> > > > > >
> > > > > > Well, that partially correct. The efifb is using the PCIe
> > > > > > resources
> > > > > > to
> > > > > > access the framebuffer and as far as I know we use that one
> > > > > > to
> > > > > > kick
> > > > > > it out.
> > > > > >
> > > > > > The stolen memory we get over e820/registers is separate to
> > > > > > that.
> > >
> > > How is the stolen memory communicated to the driver ?  That host
> > > physical
> > > memory probably has to be mapped at the same guest physical address
> > > for
> > > the magic to work, right ?
> >
> > Correct.  The driver reads the physical location of that memory from
> > hardware registers.  Removing this chunk of code from gmc_v9_0.c will
> > force the driver to use the BAR, but I'm not sure if there are any
> > other places in the driver that make assumptions about using the
> > physical host address or not on APUs off hand.
> >
> >         if ((adev->flags & AMD_IS_APU) ||
> >             (adev->gmc.xgmi.supported &&
> >              adev->gmc.xgmi.connected_to_cpu)) {
> >                 adev->gmc.aper_base =
> >                         adev->gfxhub.funcs->get_mc_fb_offset(adev) +
> >                         adev->gmc.xgmi.physical_node_id *
> >                         adev->gmc.xgmi.node_segment_size;
> >                 adev->gmc.aper_size = adev->gmc.real_vram_size;
> >         }
> >
> >
> >
> > >
> > > > > >
> > > > > > > ... which brings me to a point that's been puzzling me for
> > > > > > > some
> > > > > > > time, which is
> > > > > > > that as the hw init fails, the efifb driver is still using
> > > > > > > the
> > > > > > > framebuffer.
> > > > > >
> > > > > > No, it isn't. You are probably just still seeing the same
> > > > > > screen.
> > > > > >
> > > > > > The issue is most likely that while efi was kicked out nobody
> > > > > > re-programmed the display hardware to show something
> > > > > > different.
> > > > > >
> > > > > > > Am I right in suspecting that efifb should get stripped of
> > > > > > > its
> > > > > > > ownership of the
> > > > > > > fb aperture first, and that if I don't get a black screen
> > > > > > > on
> > > > > > > hw_init failure
> > > > > > > that issue should be the first focus point ?
> > > > > >
> > > > > > You assumption with the black screen is incorrect. Since the
> > > > > > hardware
> > > > > > works independent even if you kick out efi you still have the
> > > > > > same
> > > > > > screen content, you just can't update it anymore.
> > > > >
> > > > > It's not only that the screen keeps its contents, it's that the
> > > > > dom0
> > > > > happily continues updating it.
> > > >
> > > > If the hypevisor is using efifb, then yes that could be a problem
> > > > as
> > > > the hypervisor could be writing to the efifb resources which ends
> > > > up
> > > > writing to the same physical memory.  That applies to any GPU on
> > > > a
> > > > UEFI system.  You'll need to make sure efifb is not in use in the
> > > > hypervisor.
> > >
> > > That remark evokes several things to me.  First one is that every
> > > time
> > > I've tried booting with efifb disabled in dom0, there was no
> > > visible
> > > improvements in the guest driver - i.i. I really have to dig how
> > > vram mapping
> > > is performed and check things are as expected anyway.
> >
> > Ultimately you end up at the same physical memory.  efifb uses the
> > PCI
> > BAR which points to the same physical memory that the driver directly
> > maps.
> >
> > >
> > > The other is that, when dom0 cannot use efifb, entering a luks key
> > > is
> > > suddenly less user-friendly.  But in theory I'd think we could
> > > overcome
> > > this by letting dom0 use efifb until ready to start the guest, a
> > > simple
> > > driver unbind at the right moment should be expected to work, right
> > > ?
> > > Going further and allowing the guest to use efifb on its own could
> > > possibly be more tricky (starting with a different state?) but does
> > > not seem to sound completely outlandish either - or does it ?
> > >
> >
> > efifb just takes whatever hardware state the GOP driver in the pre-OS
> > environment left the GPU in.  Once you have a driver loaded in the
> > OS,
> > that state is gone so I I don't see much value in using efifb once
> > you
> > have a real driver in the mix.  If you want a console on the host,
> > it's probably better to use 2 GPU or just load the real driver as
> > needed in both the host and guest.
>
> My point is essentially making sure we always have a usable display.
> Dom0 will essentially use it for entering luks key (but having boot logs
> visible may also be useful for some troubleshooting), and I was figuring
> out that once dom0 has relinquished it to start a guest with passthrough,
> the guest might as well make use of it before it can start amdgpu.
> Could be useful as a first step of seeing the GPU in the guest, in
> case there are more issues to be solved to be able to start amdgpu.

Something has to program the GPU to get the displays up.  You need a
driver for that.  Once the OS has loaded the UEFI GOP driver is gone.

Alex

>
> >
> > > >
> > > > Alex
> > > >
> > > >
> > > > >
> > > > > > But putting efi asside what Alex pointed out pretty much
> > > > > > breaks
> > > > > > your
> > > > > > neck trying to forward the device. You maybe could try to
> > > > > > hack
> > > > > > the
> > > > > > driver to use the PCIe BAR for framebuffer access, but that
> > > > > > might
> > > > > > be
> > > > > > quite a bit slower.
> > > > > >
> > > > > > Regards,
> > > > > > Christian.
> > > > > >
> > > > > > >
> > > > > > >> Alex
> > > > > > >>
> > > > > > >> On Mon, Dec 13, 2021 at 3:29 PM Alex Deucher
> > > > > > >> <alexdeucher at gmail.com>
> > > > > > >> wrote:
> > > > > > >>> On Sun, Dec 12, 2021 at 5:19 PM Yann Dirson
> > > > > > >>> <ydirson at free.fr>
> > > > > > >>> wrote:
> > > > > > >>>> Alex wrote:
> > > > > > >>>>> On Mon, Dec 6, 2021 at 4:36 PM Yann Dirson
> > > > > > >>>>> <ydirson at free.fr>
> > > > > > >>>>> wrote:
> > > > > > >>>>>> Hi Alex,
> > > > > > >>>>>>
> > > > > > >>>>>>> We have not validated virtualization of our
> > > > > > >>>>>>> integrated
> > > > > > >>>>>>> GPUs.  I
> > > > > > >>>>>>> don't
> > > > > > >>>>>>> know that it will work at all.  We had done a bit of
> > > > > > >>>>>>> testing but
> > > > > > >>>>>>> ran
> > > > > > >>>>>>> into the same issues with the PSP, but never had a
> > > > > > >>>>>>> chance
> > > > > > >>>>>>> to
> > > > > > >>>>>>> debug
> > > > > > >>>>>>> further because this feature is not productized.
> > > > > > >>>>>> ...
> > > > > > >>>>>>> You need a functional PSP to get the GPU driver up
> > > > > > >>>>>>> and
> > > > > > >>>>>>> running.
> > > > > > >>>>>> Ah, thanks for the hint :)
> > > > > > >>>>>>
> > > > > > >>>>>> I guess that if I want to have any chance to get the
> > > > > > >>>>>> PSP
> > > > > > >>>>>> working
> > > > > > >>>>>> I'm
> > > > > > >>>>>> going to need more details on it.  A quick search some
> > > > > > >>>>>> time
> > > > > > >>>>>> ago
> > > > > > >>>>>> mostly
> > > > > > >>>>>> brought reverse-engineering work, rather than official
> > > > > > >>>>>> AMD
> > > > > > >>>>>> doc.
> > > > > > >>>>>>   Are
> > > > > > >>>>>> there some AMD resources I missed ?
> > > > > > >>>>> The driver code is pretty much it.
> > > > > > >>>> Let's try to shed some more light on how things work,
> > > > > > >>>> taking
> > > > > > >>>> as
> > > > > > >>>> excuse
> > > > > > >>>> psp_v12_0_ring_create().
> > > > > > >>>>
> > > > > > >>>> First, register access through [RW]REG32_SOC15() is
> > > > > > >>>> implemented
> > > > > > >>>> in
> > > > > > >>>> terms of __[RW]REG32_SOC15_RLC__(), which is basically a
> > > > > > >>>> [RW]REG32(),
> > > > > > >>>> except it has to be more complex in the SR-IOV case.
> > > > > > >>>> Has the RLC anything to do with SR-IOV ?
> > > > > > >>> When running the driver on a SR-IOV virtual function
> > > > > > >>> (VF),
> > > > > > >>> some
> > > > > > >>> registers are not available directly via the VF's MMIO
> > > > > > >>> aperture
> > > > > > >>> so
> > > > > > >>> they need to go through the RLC.  For bare metal or
> > > > > > >>> passthrough
> > > > > > >>> this
> > > > > > >>> is not relevant.
> > > > > > >>>
> > > > > > >>>> It accesses registers in the MMIO range of the MP0 IP,
> > > > > > >>>> and
> > > > > > >>>> the
> > > > > > >>>> "MP0"
> > > > > > >>>> name correlates highly with MMIO accesses in
> > > > > > >>>> PSP-handling
> > > > > > >>>> code.
> > > > > > >>>> Is "MP0" another name for PSP (and "MP1" for SMU) ?  The
> > > > > > >>>> MP0
> > > > > > >>>> version
> > > > > > >>> Yes.
> > > > > > >>>
> > > > > > >>>> reported at v11.0.3 by discovery seems to contradict the
> > > > > > >>>> use
> > > > > > >>>> of
> > > > > > >>>> v12.0
> > > > > > >>>> for RENOIR as set by soc15_set_ip_blocks(), or do I miss
> > > > > > >>>> something ?
> > > > > > >>> Typo in the ip discovery table on renoir.
> > > > > > >>>
> > > > > > >>>> More generally (and mostly out of curiosity while we're
> > > > > > >>>> at
> > > > > > >>>> it),
> > > > > > >>>> do we
> > > > > > >>>> have a way to match IPs listed at discovery time with
> > > > > > >>>> the
> > > > > > >>>> ones
> > > > > > >>>> used
> > > > > > >>>> in the driver ?
> > > > > > >>> In general, barring typos, the code is shared at the
> > > > > > >>> major
> > > > > > >>> version
> > > > > > >>> level.  The actual code may or may not need changes to
> > > > > > >>> handle
> > > > > > >>> minor
> > > > > > >>> revision changes in an IP.  The driver maps the IP
> > > > > > >>> versions
> > > > > > >>> from
> > > > > > >>> the
> > > > > > >>> ip discovery table to the code contained in the driver.
> > > > > > >>>
> > > > > > >>>> ---
> > > > > > >>>>
> > > > > > >>>> As for the register names, maybe we could have a short
> > > > > > >>>> explanation of
> > > > > > >>>> how they are structured ?  Eg. mmMP0_SMN_C2PMSG_69: that
> > > > > > >>>> seems
> > > > > > >>>> to
> > > > > > >>>> be
> > > > > > >>>> a MMIO register named "C2PMSG_69" in the "MP0" IP, but
> > > > > > >>>> I'm
> > > > > > >>>> not
> > > > > > >>>> sure
> > > > > > >>>> of the "SMN" part -- that could refer to the "System
> > > > > > >>>> Management
> > > > > > >>>> Network",
> > > > > > >>>> described in [0] as an internal bus.  Are we accessing
> > > > > > >>>> this
> > > > > > >>>> register
> > > > > > >>>> through this SMN ?
> > > > > > >>> These registers are just mailboxes for the PSP firmware.
> > > > > > >>>  All
> > > > > > >>> of
> > > > > > >>> the
> > > > > > >>> C2PMSG registers functionality is defined by the PSP
> > > > > > >>> firmware.
> > > > > > >>>   They
> > > > > > >>> are basically scratch registers used to communicate
> > > > > > >>> between
> > > > > > >>> the
> > > > > > >>> driver
> > > > > > >>> and the PSP firmware.
> > > > > > >>>
> > > > > > >>>>
> > > > > > >>>>>   On APUs, the PSP is shared with
> > > > > > >>>>> the CPU and the rest of the platform.  The GPU driver
> > > > > > >>>>> just
> > > > > > >>>>> interacts
> > > > > > >>>>> with it for a few specific tasks:
> > > > > > >>>>> 1. Loading Trusted Applications (e.g., trusted firmware
> > > > > > >>>>> applications
> > > > > > >>>>> that run on the PSP for specific functionality, e.g.,
> > > > > > >>>>> HDCP
> > > > > > >>>>> and
> > > > > > >>>>> content
> > > > > > >>>>> protection, etc.)
> > > > > > >>>>> 2. Validating and loading firmware for other engines on
> > > > > > >>>>> the
> > > > > > >>>>> SoC.
> > > > > > >>>>>   This
> > > > > > >>>>> is required to use those engines.
> > > > > > >>>> Trying to understand in more details how we start the
> > > > > > >>>> PSP
> > > > > > >>>> up, I
> > > > > > >>>> noticed
> > > > > > >>>> that psp_v12_0 has support for loading a sOS firmware,
> > > > > > >>>> but
> > > > > > >>>> never
> > > > > > >>>> calls
> > > > > > >>>> init_sos_microcode() - and anyway there is no sos
> > > > > > >>>> firmware
> > > > > > >>>> for
> > > > > > >>>> renoir
> > > > > > >>>> and green_sardine, which seem to be the only ASICs with
> > > > > > >>>> this
> > > > > > >>>> PSP
> > > > > > >>>> version.
> > > > > > >>>> Is it something that's just not been completely wired up
> > > > > > >>>> yet
> > > > > > >>>> ?
> > > > > > >>> On APUs, the PSP is shared with the CPU so the PSP
> > > > > > >>> firmware
> > > > > > >>> is
> > > > > > >>> part
> > > > > > >>> of
> > > > > > >>> the sbios image.  The driver doesn't load it.  We only
> > > > > > >>> load
> > > > > > >>> it on
> > > > > > >>> dGPUs where the driver is responsible for the chip
> > > > > > >>> initialization.
> > > > > > >>>
> > > > > > >>>> That also rings a bell, that we have nothing about
> > > > > > >>>> Secure OS
> > > > > > >>>> in
> > > > > > >>>> the doc
> > > > > > >>>> yet (not even the acronym in the glossary).
> > > > > > >>>>
> > > > > > >>>>
> > > > > > >>>>> I'm not too familiar with the PSP's path to memory from
> > > > > > >>>>> the
> > > > > > >>>>> GPU
> > > > > > >>>>> perspective.  IIRC, most memory used by the PSP goes
> > > > > > >>>>> through
> > > > > > >>>>> carve
> > > > > > >>>>> out
> > > > > > >>>>> "vram" on APUs so it should work, but I would double
> > > > > > >>>>> check
> > > > > > >>>>> if
> > > > > > >>>>> there
> > > > > > >>>>> are any system memory allocations that used to interact
> > > > > > >>>>> with
> > > > > > >>>>> the PSP
> > > > > > >>>>> and see if changing them to vram helps.  It does work
> > > > > > >>>>> with
> > > > > > >>>>> the
> > > > > > >>>>> IOMMU
> > > > > > >>>>> enabled on bare metal, so it should work in passthrough
> > > > > > >>>>> as
> > > > > > >>>>> well
> > > > > > >>>>> in
> > > > > > >>>>> theory.
> > > > > > >>>> I can see a single case in the PSP code where GTT is
> > > > > > >>>> used
> > > > > > >>>> instead
> > > > > > >>>> of
> > > > > > >>>> vram: to create fw_pri_bo when SR-IOV is not used (and
> > > > > > >>>> there
> > > > > > >>>> has
> > > > > > >>>> to be a reason, since the SR-IOV code path does use
> > > > > > >>>> vram).
> > > > > > >>>> Changing it to vram does not make a difference, but then
> > > > > > >>>> the
> > > > > > >>>> only bo that seems to be used at that point is the one
> > > > > > >>>> for
> > > > > > >>>> the
> > > > > > >>>> psp ring,
> > > > > > >>>> which is allocated in vram, so I'm not too much
> > > > > > >>>> surprised.
> > > > > > >>>>
> > > > > > >>>> Maybe I should double-check bo_create calls to hunt for
> > > > > > >>>> more
> > > > > > >>>> ?
> > > > > > >>> We looked into this a bit ourselves and ran into the same
> > > > > > >>> issues.
> > > > > > >>> We'd probably need to debug this with the PSP team to
> > > > > > >>> make
> > > > > > >>> further
> > > > > > >>> progress, but this was not productized so neither team
> > > > > > >>> had
> > > > > > >>> the
> > > > > > >>> resources to delve further.
> > > > > > >>>
> > > > > > >>> Alex
> > > > > > >>>
> > > > > > >>>>
> > > > > > >>>> [0]
> > > > > > >>>> https://github.com/PSPReverse/psp-docs/blob/master/masterthesis-eichner-psp-2020.pdf
> > > > > >
> > > > > >
> > > >
> >