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Date:   Wed, 2 Dec 2020 14:22:53 -0600
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     "Surendrakumar Upadhyay, TejaskumarX" 
        <tejaskumarx.surendrakumar.upadhyay@intel.com>
Cc:     Jesse Barnes <jsbarnes@google.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Linux PCI <linux-pci@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        X86 ML <x86@kernel.org>, Borislav Petkov <bp@alien8.de>,
        "De Marchi, Lucas" <lucas.demarchi@intel.com>,
        "Roper, Matthew D" <matthew.d.roper@intel.com>,
        "Pandey, Hariom" <hariom.pandey@intel.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        "Vivi, Rodrigo" <rodrigo.vivi@intel.com>,
        David Airlie <airlied@linux.ie>
Subject: Re: [PATCH] x86/gpu: add JSL stolen memory support
Message-ID: <20201202202253.GA1467966@bjorn-Precision-5520>
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On Wed, Dec 02, 2020 at 05:21:58AM +0000, Surendrakumar Upadhyay, TejaskumarX wrote:
> Yes it fails all the tests which are allocating from this stolen
> memory bunch. For example IGT tests like "
> igt@kms_frontbuffer_tracking@-[fbc|fbcpsr].* |
> igt@kms_fbcon_fbt@fbc.* " are failing as they totally depend to work
> on stolen memory.

I'm sure that means something to graphics developers, but I have no
idea!  Do you have URLs for the test case source, outputs, dmesg log,
lspci info, bug reports, etc?

> > -----Original Message-----
> > From: Bjorn Helgaas <helgaas@kernel.org>
> > Sent: 30 November 2020 22:21
> > To: Surendrakumar Upadhyay, TejaskumarX
> > <tejaskumarx.surendrakumar.upadhyay@intel.com>
> > Cc: Jesse Barnes <jsbarnes@google.com>; Daniel Vetter <daniel@ffwll.ch>;
> > Joonas Lahtinen <joonas.lahtinen@linux.intel.com>; Linux PCI <linux-
> > pci@vger.kernel.org>; Linux Kernel Mailing List <linux-
> > kernel@vger.kernel.org>; X86 ML <x86@kernel.org>; Borislav Petkov
> > <bp@alien8.de>; De Marchi, Lucas <lucas.demarchi@intel.com>; Roper,
> > Matthew D <matthew.d.roper@intel.com>; Pandey, Hariom
> > <hariom.pandey@intel.com>; Jani Nikula <jani.nikula@linux.intel.com>; Vivi,
> > Rodrigo <rodrigo.vivi@intel.com>; David Airlie <airlied@linux.ie>
> > Subject: Re: [PATCH] x86/gpu: add JSL stolen memory support
> > 
> > On Mon, Nov 30, 2020 at 10:44:14AM +0000, Surendrakumar Upadhyay,
> > TejaskumarX wrote:
> > > Hi All,
> > >
> > > Are we merging this patch in?
> > 
> > Does it fix something?  If something is broken without this patch, can we
> > collect information about exactly what is broken and how it fails?
> > 
> > But I don't object if somebody else wants to apply this.
> > 
> > > > -----Original Message-----
> > > > From: Jesse Barnes <jsbarnes@google.com>
> > > > Sent: 20 November 2020 03:32
> > > > To: Bjorn Helgaas <helgaas@kernel.org>
> > > > Cc: Daniel Vetter <daniel@ffwll.ch>; Joonas Lahtinen
> > > > <joonas.lahtinen@linux.intel.com>; Surendrakumar Upadhyay,
> > > > TejaskumarX <tejaskumarx.surendrakumar.upadhyay@intel.com>; Linux
> > > > PCI <linux- pci@vger.kernel.org>; Linux Kernel Mailing List <linux-
> > > > kernel@vger.kernel.org>; X86 ML <x86@kernel.org>; Borislav Petkov
> > > > <bp@alien8.de>; De Marchi, Lucas <lucas.demarchi@intel.com>; Roper,
> > > > Matthew D <matthew.d.roper@intel.com>; Pandey, Hariom
> > > > <hariom.pandey@intel.com>; Jani Nikula
> > > > <jani.nikula@linux.intel.com>; Vivi, Rodrigo
> > > > <rodrigo.vivi@intel.com>; David Airlie <airlied@linux.ie>
> > > > Subject: Re: [PATCH] x86/gpu: add JSL stolen memory support
> > > >
> > > > On Thu, Nov 19, 2020 at 11:19 AM Bjorn Helgaas <helgaas@kernel.org>
> > > > wrote:
> > > > >
> > > > > [+cc Jesse]
> > > > >
> > > > > On Thu, Nov 19, 2020 at 10:37:10AM +0100, Daniel Vetter wrote:
> > > > > > On Thu, Nov 19, 2020 at 12:14 AM Bjorn Helgaas
> > > > > > <helgaas@kernel.org>
> > > > wrote:
> > > > > > > On Wed, Nov 18, 2020 at 10:57:26PM +0100, Daniel Vetter wrote:
> > > > > > > > On Wed, Nov 18, 2020 at 5:02 PM Bjorn Helgaas
> > > > <helgaas@kernel.org> wrote:
> > > > > > > > > On Fri, Nov 06, 2020 at 10:39:16AM +0100, Daniel Vetter wrote:
> > > > > > > > > > On Thu, Nov 5, 2020 at 3:17 PM Bjorn Helgaas
> > > > <helgaas@kernel.org> wrote:
> > > > > > > > > > > On Thu, Nov 05, 2020 at 11:46:06AM +0200, Joonas
> > > > > > > > > > > Lahtinen
> > > > wrote:
> > > > > > > > > > > > Quoting Bjorn Helgaas (2020-11-04 19:35:56)
> > > > > > > > > > > > > [+cc Jani, Joonas, Rodrigo, David, Daniel]
> > > > > > > > > > > > >
> > > > > > > > > > > > > On Wed, Nov 04, 2020 at 05:35:06PM +0530, Tejas
> > > > > > > > > > > > > Upadhyay
> > > > wrote:
> > > > > > > > > > > > > > JSL re-uses the same stolen memory as ICL and EHL.
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> > > > > > > > > > > > > > Cc: Matt Roper <matthew.d.roper@intel.com>
> > > > > > > > > > > > > > Signed-off-by: Tejas Upadhyay
> > > > > > > > > > > > > > <tejaskumarx.surendrakumar.upadhyay@intel.com>
> > > > > > > > > > > > >
> > > > > > > > > > > > > I don't plan to do anything with this since
> > > > > > > > > > > > > previous similar patches have gone through some
> > > > > > > > > > > > > other tree, so this is
> > > > just kibitzing.
> > > > > > > > > > > > >
> > > > > > > > > > > > > But the fact that we have this long list of Intel
> > > > > > > > > > > > > devices [1] that constantly needs updates [2] is a
> > > > > > > > > > > > > hint that
> > > > something is wrong.
> > > > > > > > > > > >
> > > > > > > > > > > > We add an entry for every new integrated graphics
> > > > > > > > > > > > platform. Once the platform is added, there have not
> > > > > > > > > > > > been
> > > > changes lately.
> > > > > > > > > > > >
> > > > > > > > > > > > > IIUC the general idea is that we need to discover
> > > > > > > > > > > > > Intel gfx memory by looking at device-dependent
> > > > > > > > > > > > > config
> > > > space and add it to the E820 map.
> > > > > > > > > > > > > Apparently the quirks discover this via PCI config
> > > > > > > > > > > > > registers like I830_ESMRAMC, I845_ESMRAMC, etc,
> > > > > > > > > > > > > and tell the driver about it via the global
> > > > "intel_graphics_stolen_res"?
> > > > > > > > > > > >
> > > > > > > > > > > > We discover what is called the graphics data stolen
> > > > > > > > > > > > memory. It is regular system memory range that is
> > > > > > > > > > > > not CPU accessible. It is accessible by the integrated
> > graphics only.
> > > > > > > > > > > >
> > > > > > > > > > > > See:
> > > > > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torv
> > > > > > > > > > > > alds
> > > > > > > > > > > > /linux.git/commit/arch/x86/kernel/early-quirks.c?h=v
> > > > > > > > > > > > 5.10
> > > > > > > > > > > > -rc2&id=814c5f1f52a4beb3710317022acd6ad34fc0b6b9
> > > > > > > > > > > >
> > > > > > > > > > > > > That's not the way this should work.  There should
> > > > > > > > > > > > > some generic, non device-dependent PCI or ACPI
> > > > > > > > > > > > > method to discover the memory used, or at least
> > > > > > > > > > > > > some way to do it in
> > > > the driver instead of early arch code.
> > > > > > > > > > > >
> > > > > > > > > > > > It's used by the early BIOS/UEFI code to set up
> > > > > > > > > > > > initial
> > > > framebuffer.
> > > > > > > > > > > > Even if i915 driver is never loaded, the memory
> > > > > > > > > > > > ranges still need to be fixed. They source of the
> > > > > > > > > > > > problem is that the OEM BIOS which are not under our
> > > > > > > > > > > > control get the
> > > > programming wrong.
> > > > > > > > > > > >
> > > > > > > > > > > > We used to detect the memory region size again at
> > > > > > > > > > > > i915 initialization but wanted to eliminate the code
> > > > > > > > > > > > duplication and resulting subtle bugs that caused.
> > > > > > > > > > > > Conclusion back then was that storing the struct
> > > > > > > > > > > > resource in
> > > > memory is the best trade-off.
> > > > > > > > > > > >
> > > > > > > > > > > > > How is this *supposed* to work?  Is there
> > > > > > > > > > > > > something we can do in E820 or other resource
> > > > > > > > > > > > > management that would
> > > > make this easier?
> > > > > > > > > > > >
> > > > > > > > > > > > The code was added around Haswell (HSW) device
> > > > > > > > > > > > generation to mitigate bugs in BIOS. It is
> > > > > > > > > > > > traditionally hard to get all OEMs to fix their BIOS
> > > > > > > > > > > > when things work for Windows. It's only later years
> > > > > > > > > > > > when some laptop models
> > > > are intended to be sold with Linux.
> > > > > > > > > > > >
> > > > > > > > > > > > The alternative would be to get all the OEM to fix
> > > > > > > > > > > > their BIOS for Linux, but that is not very realistic
> > > > > > > > > > > > given past experiences. So it seems a better choice
> > > > > > > > > > > > to to add new line per platform generation to make
> > > > > > > > > > > > sure the users can
> > > > boot to Linux.
> > > > > > > > > > >
> > > > > > > > > > > How does Windows do this?  Do they have to add similar
> > > > > > > > > > > code for each new platform?
> > > > > > > > > >
> > > > > > > > > > Windows is chicken and doesn't move any mmio bar around
> > > > > > > > > > on its
> > > > own.
> > > > > > > > > > Except if the bios explicitly told it somehow (e.g. for
> > > > > > > > > > the 64bit bar stuff amd recently announced for windows,
> > > > > > > > > > that linux supports since years by moving the bar). So
> > > > > > > > > > except if you want to preemptively disable the pci code
> > > > > > > > > > that does this anytime there's an intel gpu, this is what we
> > have to do.
> > > > > > > > >
> > > > > > > > > I think Windows *does* move BARs (they use the more
> > > > > > > > > generic terminology of "rebalancing PNP resources") in
> > > > > > > > > some cases [3,4].  Of course, I'm pretty sure Windows will
> > > > > > > > > only assign PCI resources inside the windows advertised in
> > > > > > > > > the host bridge
> > > > _CRS.
> > > > > > > > >
> > > > > > > > > Linux *used* to ignore that host bridge _CRS and could set
> > > > > > > > > BARs to addresses that appeared available but were in fact
> > > > > > > > > used by the platform somehow.  But Linux has been paying
> > > > > > > > > attention to host bridge _CRS for a long time now, so it
> > > > > > > > > should also only assign resources inside those windows.
> > > > > > > >
> > > > > > > > If this behaviour is newer than the addition of these quirks
> > > > > > > > then yeah they're probably not needed anymore, and we can
> > > > > > > > move all this back into the driver. Do you have the commit
> > > > > > > > when pci core started observing _CRS on the host bridge?
> > > > > > >
> > > > > > > I think the most relevant commit is this:
> > > > > > >
> > > > > > >   2010-02-23 7bc5e3f2be32 ("x86/PCI: use host bridge _CRS info
> > > > > > > by default on 2008 and newer machines")
> > > > > > >
> > > > > > > but the earliest quirk I found is over three years later:
> > > > > > >
> > > > > > >   2013-07-26 814c5f1f52a4 ("x86: add early quirk for reserving
> > > > > > > Intel graphics stolen memory v5")
> > > > > > >
> > > > > > > So there must be something else going on.  814c5f1f52a4
> > > > > > > mentions a couple bug reports.  The dmesg from 66726 [5] shows
> > > > > > > that we *are* observing the host bridge _CRS, but Linux just
> > > > > > > used the BIOS configuration without changing anything:
> > > > > > >
> > > > > > >   BIOS-e820: [mem 0x000000007f49_f000-0x000000007f5f_ffff]
> > usable
> > > > > > >   BIOS-e820: [mem 0x00000000fec0_0000-0x00000000fec0_0fff]
> > > > reserved
> > > > > > >   PCI: Using host bridge windows from ACPI; if necessary, use
> > > > "pci=nocrs" and report a bug
> > > > > > >   ACPI: PCI Root Bridge [PCI0] (domain 0000 [bus 00-ff])
> > > > > > >   pci_bus 0000:00: root bus resource [mem 0x7f70_0000-0xffff_ffff]
> > > > > > >   pci 0000:00:1c.0: PCI bridge to [bus 01]
> > > > > > >   pci 0000:00:1c.0:   bridge window [io  0x1000-0x1fff]
> > > > > > >   pci 0000:00:1c.0:   bridge window [mem 0xfe90_0000-0xfe9f_ffff]
> > > > > > >   pci 0000:00:1c.0:   bridge window [mem 0x7f70_0000-0x7f8f_ffff
> > 64bit
> > > > pref]
> > > > > > >   pci 0000:01:00.0: [1814:3090] type 00 class 0x028000
> > > > > > >   pci 0000:01:00.0: reg 10: [mem 0xfe90_0000-0xfe90_ffff]
> > > > > > >   [drm:i915_stolen_to_physical] *ERROR* conflict detected with
> > > > > > > stolen region: [0x7f80_0000 - 0x8000_0000]
> > > > > > >
> > > > > > > So the BIOS programmed the 00:1c.0 bridge prefetchable window
> > > > > > > to [mem 0x7f70_0000-0x7f8f_ffff], and i915 thinks that's a conflict.
> > > > > > >
> > > > > > > On this system, there are no PCI BARs in that range.  01:00.0
> > > > > > > looks like a Ralink RT3090 Wireless 802.11n device that only
> > > > > > > has a non-prefetchable BAR at [mem 0xfe90_0000-0xfe90_ffff].
> > > > > > >
> > > > > > > I don't know the details of the conflict.  IIUC, Joonas said
> > > > > > > the stolen memory is accessible only by the integrated
> > > > > > > graphics, not by the CPU.  The bridge window is CPU
> > > > > > > accessible, of course, and the [mem 0x7f70_0000-0x7f8f_ffff]
> > > > > > > range contains the addresses the CPU uses for programmed I/O to
> > BARs below the bridge.
> > > > > > >
> > > > > > > The graphics accesses sound like they would be DMA in the
> > > > > > > *bus* address space, which is frequently, but not always,
> > > > > > > identical to the CPU address space.
> > > > > >
> > > > > > So apparently on some platforms the conflict is harmless because
> > > > > > the BIOS puts BARs and stuff over it from boot-up, and things work:
> > > > > > 0b6d24c01932 ("drm/i915: Don't complain about stolen conflicts
> > > > > > on
> > > > > > gen3") But we also had conflict reports on other machines.
> > > > >
> > > > > The bug reports mentioned in 814c5f1f52a4 ("x86: add early quirk
> > > > > for reserving Intel graphics stolen memory v5") and 0b6d24c01932
> > > > > ("drm/i915: Don't complain about stolen conflicts on gen3") seem
> > > > > to be basically complaints about the *message*, not anything
> > > > > that's actually broken.
> > > > >
> > > > > Jesse's comment [6]:
> > > > >
> > > > >   Given the decode priority on our GMCHs, it's fine if the regions
> > > > >   overlap.  However it doesn't look like there's a nice way to detect
> > > > >   it.  In this case, part of the range occupied by the stolen space is
> > > > >   simply "reserved" per the E820, but the rest of it is under the bus
> > > > >   0 range (which kind of makes sense too).
> > > > >
> > > > > sounds relevant but I don't know enough to interpret it.  I added
> > > > > Jesse in case he wants to comment.
> > > > >
> > > > > > GPU does all its access with CPU address space (after the iommu,
> > > > > > which is entirely integrated). So I'm not sure whether we've
> > > > > > seen something go boom or whether reserving that resource was
> > > > > > just precaution in
> > > > > > eaba1b8f3379 ("drm/i915: Verify that our stolen memory doesn't
> > > > > > conflict"), it's all a bit way back in history.
> > > > > >
> > > > > > So really not sure what to do here or what the risks are.
> > > > >
> > > > > I'm not either.  Seems like we're not really converging on
> > > > > anything useful we can do at this point.  The only thing I can
> > > > > think of would be to collect data about actual failures (not just warning
> > messages).
> > > > > That might lead to something we could improve in the future.
> > > >
> > > > I don't have any brilliant ideas here unfortunately.  Maybe it's
> > > > worth talking to some of the Windows folks internally to see how
> > > > these ranges are handled these days and matching it?  Historically
> > > > this has been an area fraught with danger because getting things
> > > > wrong can lead to corruption of various kinds or boot hangs.
> > > >
> > > > Jesse