On Tue, 2 Apr 2019 17:38:26 +0200 Laszlo Ersek <ler...@redhat.com> wrote:
> On 04/02/19 17:29, Auger Eric wrote: > > Hi Laszlo, > > > > On 4/1/19 3:07 PM, Laszlo Ersek wrote: > >> On 03/29/19 14:56, Auger Eric wrote: > >>> Hi Ard, > >>> > >>> On 3/29/19 2:14 PM, Ard Biesheuvel wrote: > >>>> On Fri, 29 Mar 2019 at 14:12, Auger Eric <eric.au...@redhat.com> wrote: > >>>>> > >>>>> Hi Shameer, > >>>>> > >>>>> On 3/29/19 10:59 AM, Shameerali Kolothum Thodi wrote: > >>>>>> > >>>>>> > >>>>>>> -----Original Message----- > >>>>>>> From: Auger Eric [mailto:eric.au...@redhat.com] > >>>>>>> Sent: 29 March 2019 09:32 > >>>>>>> To: Shameerali Kolothum Thodi <shameerali.kolothum.th...@huawei.com>; > >>>>>>> qemu-devel@nongnu.org; qemu-...@nongnu.org; imamm...@redhat.com; > >>>>>>> peter.mayd...@linaro.org; shannon.zha...@gmail.com; > >>>>>>> sa...@linux.intel.com; sebastien.bo...@intel.com > >>>>>>> Cc: Linuxarm <linux...@huawei.com>; xuwei (O) <xuw...@huawei.com>; > >>>>>>> Laszlo Ersek <ler...@redhat.com>; Ard Biesheuvel > >>>>>>> <ard.biesheu...@linaro.org>; Leif Lindholm <leif.lindh...@arm.com> > >>>>>>> Subject: Re: [PATCH v3 07/10] hw/arm/virt: Introduce opt-in feature > >>>>>>> "fdt" > >>>>>>> > >>>>>>> Hi Shameer, > >>>>>>> > >>>>>>> [ + Laszlo, Ard, Leif ] > >>>>>>> > >>>>>>> On 3/21/19 11:47 AM, Shameer Kolothum wrote: > >>>>>>>> This is to disable/enable populating DT nodes in case > >>>>>>>> any conflict with acpi tables. The default is "off". > >>>>>>> The name of the option sounds misleading to me. Also we don't really > >>>>>>> know the scope of the disablement. At the moment this just aims to > >>>>>>> prevent the hotpluggable dt nodes from being added if we boot in ACPI > >>>>>>> mode. > >>>>>>> > >>>>>>>> > >>>>>>>> This will be used in subsequent patch where cold plug > >>>>>>>> device-memory support is added for DT boot. > >>>>>>> I am concerned about the fact that in dt mode, by default, you won't > >>>>>>> see > >>>>>>> any PCDIMM nodes. > >>>>>>>> > >>>>>>>> If DT memory node support is added for cold-plugged device > >>>>>>>> memory, those memory will be visible to Guest kernel via > >>>>>>>> UEFI GetMemoryMap() and gets treated as early boot memory. > >>>>>>> Don't we have an issue in UEFI then. Normally the SRAT indicates > >>>>>>> whether > >>>>>>> the slots are hotpluggable or not. Shouldn't the UEFI code look at > >>>>>>> this > >>>>>>> info. > >>>>>> > >>>>>> Sorry I missed this part. Yes, that will be a more cleaner solution. > >>>>>> > >>>>>> Also, to be more clear on what happens, > >>>>>> > >>>>>> Guest ACPI boot with "fdt=on" , > >>>>>> > >>>>>> From kernel log, > >>>>>> > >>>>>> [ 0.000000] Early memory node ranges > >>>>>> [ 0.000000] node 0: [mem 0x0000000040000000-0x00000000bbf5ffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bbf60000-0x00000000bbffffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bc000000-0x00000000bc02ffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bc030000-0x00000000bc36ffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bc370000-0x00000000bf64ffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bf650000-0x00000000bf6dffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bf6e0000-0x00000000bf6effff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bf6f0000-0x00000000bf80ffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bf810000-0x00000000bfffffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000c0000000-0x00000000ffffffff] > >>>>>> --> This is the hotpluggable memory node from DT. > >>>>>> [ 0.000000] Zeroed struct page in unavailable ranges: 1040 pages > >>>>>> [ 0.000000] Initmem setup node 0 [mem > >>>>>> 0x0000000040000000-0x00000000ffffffff] > >>>>>> > >>>>>> > >>>>>> Guest ACPI boot with "fdt=off" , > >>>>>> > >>>>>> [ 0.000000] Movable zone start for each node > >>>>>> [ 0.000000] Early memory node ranges > >>>>>> [ 0.000000] node 0: [mem 0x0000000040000000-0x00000000bbf5ffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bbf60000-0x00000000bbffffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bc000000-0x00000000bc02ffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bc030000-0x00000000bc36ffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bc370000-0x00000000bf64ffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bf650000-0x00000000bf6dffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bf6e0000-0x00000000bf6effff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bf6f0000-0x00000000bf80ffff] > >>>>>> [ 0.000000] node 0: [mem 0x00000000bf810000-0x00000000bfffffff] > >>>>>> [ 0.000000] Zeroed struct page in unavailable ranges: 1040 pages > >>>>>> [ 0.000000] Initmem setup node 0 [mem > >>>>>> 0x0000000040000000-0x00000000bfffffff > >>>>>> > >>>>>> The hotpluggable memory node is absent from early memory nodes here. > >>>>> > >>>>> OK thank you for the example illustrating the concern. > >>>>>> > >>>>>> As you said, it could be possible to detect this node using SRAT in > >>>>>> UEFI. > >>>>> > >>>>> Let's wait for EDK2 experts on this. > >>>>> > >>>> > >>>> Happy to chime in, but I need a bit more context here. > >>>> > >>>> What is the problem, how does this path try to solve it, and why is > >>>> that a bad idea? > >>>> > >>> Sure, sorry. > >>> > >>> This series: > >>> - [PATCH v3 00/10] ARM virt: ACPI memory hotplug support, > >>> https://patchwork.kernel.org/cover/10863301/ > >>> > >>> aims to introduce PCDIMM support in qemu. In ACPI mode, it builds the > >>> SRAT and DSDT parts and relies on GED to trigger the hotplug. > >>> > >>> We noticed that if we build the hotpluggable memory dt nodes on top of > >>> the above ACPI tables, the DIMM slots are interpreted as not > >>> hotpluggable memory slots (at least we think so). > >>> > >>> We think the EDK2 GetMemoryMap() uses the dt node info and ignores the > >>> fact that those slots are exposed as hotpluggable in the SRAT for example. > >>> > >>> So in this series, we are forced to not generate the hotpluggable memory > >>> dt nodes if we want the DIMM slots to be effectively recognized as > >>> hotpluggable. > >>> > >>> Could you confirm we have a correct understanding of the EDK2 behaviour > >>> and if so, would there be any solution for EDK2 to absorb both the DT > >>> nodes and the relevant SRAT/DSDT tables and make the slots hotpluggable. > >>> > >>> At qemu level, detecting we are booting in ACPI mode and purposely > >>> removing the above mentioned DT nodes does not look straightforward. > >> > >> The firmware is not enlightened about the ACPI content that comes from > >> QEMU / fw_cfg. That ACPI content is *blindly* processed by the firmware, > >> as instructed through the ACPI linker/loader script, in order to install > >> the ACPI content for the OS. No actual information is consumed by the > >> firmware from the ACPI payload -- and that's a feature. > >> > >> The firmware does consume DT: > >> > >> - If you start QEMU *with* "-no-acpi", then the DT is both consumed by > >> the firmware (for its own information needs), and passed on to the OS. > >> > >> - If you start QEMU *without* "-no-acpi" (the default), then the DT is > >> consumed only by the firmware (for its own information needs), and the > >> DT is hidden from the OS. The OS gets only the ACPI content > >> (processed/prepared as described above). > >> > >> > >> In the firmware, the "ArmVirtPkg/HighMemDxe" driver iterates over the > >> base/size pairs in all the memory nodes in the DT. For each such base > >> address that is currently tracked as "nonexistent" in the GCD memory > >> space map, the driver currently adds the base/size range as "system > >> memory". This in turn is reflected by the UEFI memmap that the OS gets > >> to see as "conventional memory". > >> > >> If you need some memory ranges to show up as "special" in the UEFI > >> memmap, then you need to distinguish them somehow from the "regular" > >> memory areas, in the DT. And then extend "ArmVirtPkg/HighMemDxe" in the > >> firmware, so that it act upon the discriminator that you set in the DT. > >> > >> > >> Now... from a brief look at the Platform Init and UEFI specs, my > >> impression is that the hotpluggable (but presently not plugged) DIMM > >> ranges should simply be *absent* from the UEFI memmap; is that correct? > >> (I didn't check the ACPI spec, maybe it specifies the expected behavior > >> in full.) If my impression is correct, then two options (alternatives) > >> exist: > >> > >> (1) Hide the affected memory nodes -- or at least the affected base/size > >> pairs -- from the DT, in case you boot without "-no-acpi" but with an > >> external firmware loaded. Then the firmware will not expose those ranges > >> as "conventional memory" in the UEFI memmap. This approach requires no > >> changes to edk2. > >> > >> This option is precisely what Eric described up-thread, at > >> <3f0a5793-dd35-a497-2248-8eb0cd3c3a16@redhat.com">http://mid.mail-archive.com/3f0a5793-dd35-a497-2248-8eb0cd3c3a16@redhat.com>: > >> > >>> in machvirt_init, there is firmware_loaded that tells you whether you > >>> have a FW image. If this one is not set, you can induce dt. But if > >>> there is a FW it can be either DT or ACPI booted. You also have the > >>> acpi_enabled knob. > >> > >> (The "-no-acpi" cmdline option clears the "acpi_enabled" variable in > >> "vl.c"). > >> > >> So, the condition for hiding the hotpluggable memory nodes in question > >> from the DT is: > > > >> > >> (aarch64 && firmware_loaded && acpi_enabled) > > > > Thanks a lot for all those inputs! > > > > I don't get why we test aarch64 in above condition (this was useful for > > high ECAM range as the aarch32 FW was not supporting it but here, is it > > still meaningful?) > > Sorry, I should have clarified that. Yes, it is meaningful: > > While UEFI has bindings for both 32-bit and 64-bit ARM, ACPI has a > 64-bit-only binding for ARM. (And you can have UEFI without ACPI, but > not the reverse, on ARM.) So if you run the 32-bit build of the > ArmVirtQemu firmware, you get no ACPI at all; all you can rely on with > the OS is the DT. > > This "bitness distinction" is implemented in the firmware already. If > you hid the memory nodes from the DT under the condition > > (!aarch64 && firmware_loaded && acpi_enabled) > > then the nodes would not be seen by the OS at all (because > "acpi_enabled" is irrelevant for the 32-bit build of ArmVirtQemu, and > all the OS can ever get is DT). It's getting tricky and I don't like a bit that we are trying to carter 64 bit only UEFI build (or any other build) on QEMU side. Also Peter has a valid about guessing on QEMU side (that's usually a source of problem in the future). Perhaps we should reconsider and think about marking hotplugbbale RAM in DT and let firmware to exclude it from memory map. > Thanks, > Laszlo > > > > > Thanks > > > > Eric > > > >> > >> > >> (2) Invent and set an "ignore me, firmware" property for the > >> hotpluggable memory nodes in the DT, and update the firmware to honor > >> that property. > >> > >> Thanks > >> Laszlo > >> >
