Andy Shevchenko <andy.shevchenko@xxxxxxxxx> writes: > On Tue, Jan 21, 2020 at 12:18:03AM +0100, Ard Biesheuvel wrote: >> On Mon, 20 Jan 2020 at 23:31, Andy Shevchenko <andy.shevchenko@xxxxxxxxx> wrote: >> > On Mon, Jan 20, 2020 at 9:28 PM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote: >> > > Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> writes: >> > > > On Sat, Dec 17, 2016 at 06:57:21PM +0800, Dave Young wrote: > > ... > >> > > > Can we apply these patches for now until you will find better >> > > > solution? >> > > >> > > Not a chance. The patches don't apply to any kernel in the git history. >> > > >> > > Which may be part of your problem. You are or at least were running >> > > with code that has not been merged upstream. >> > >> > It's done against linux-next. >> > Applied clearly. (Not the version in this more than yearly old series >> > of course, that's why I told I can resend) >> > >> > > > P.S. I may resend them rebased on recent vanilla. >> > > >> > > Second. I looked at your test results and they don't directly make >> > > sense. dmidecode bypasses the kernel completely or it did last time >> > > I looked so I don't know why you would be using that to test if >> > > something in the kernel is working. >> > > >> > > However dmidecode failing suggests that the actual problem is something >> > > in the first kernel is stomping the dmi tables. >> > >> > See below. >> > >> > > Adding a command line option won't fix stomped tables. >> > >> > It provides a mechanism, which seems to be absent, to the second >> > kernel to know where to look for SMBIOS tables. >> > >> > > So what I would suggest is: >> > > a) Verify that dmidecode works before kexec. >> > >> > Yes, it does. >> > >> > > b) Test to see if dmidecode works after kexec. >> > >> > No, it doesn't. >> > >> > > c) Once (a) shows that dmidecode works and (b) shows that dmidecode >> > > fails figure out what is stomping your dmi tables during or before >> > > kexec and that is what should get fixed. >> > >> > The problem here as I can see it that EFI and kexec protocols are not >> > friendly to each other. >> > I'm not an expert in either. That's why I'm asking for possible >> > solutions. And this needs to be done in kernel to allow drivers to >> > work. >> > >> > Does the >> > >> > commit 4996c02306a25def1d352ec8e8f48895bbc7dea9 >> > Author: Takao Indoh <indou.takao@xxxxxxxxxxxxxx> >> > Date: Thu Jul 14 18:05:21 2011 -0400 >> > >> > ACPI: introduce "acpi_rsdp=" parameter for kdump >> > >> > description shed a light on this? >> > >> > > Now using a non-efi method of dmi detection relies on the >> > > tables being between 0xF0000 and 0x10000. AKA the last 64K >> > > of the first 1MiB of memory. You might check to see if your >> > > dmi tables are in that address range. >> > >> > # dmidecode --no-sysfs >> > # dmidecode 3.2 >> > Scanning /dev/mem for entry point. >> > # No SMBIOS nor DMI entry point found, sorry. >> > >> > === with patch applied === >> > # dmidecode >> > ... >> > Release Date: 03/10/2015 >> > ... >> > >> > > >> > > Otherwise I suspect the good solution is to give efi it's own page >> > > tables in the kernel and switch to it whenever efi functions are called. >> > > >> > >> > > But on 32bit the Linux kernel has historically been just fine directly >> > > accessing the hardware, and ignoring efi and all of the other BIOS's. >> > >> > It seems not only for 32-bit Linux kernel anymore. MS Surface 3 runs >> > 64-bit code. >> > >> > > So if that doesn't work on Intel Galileo that is probably a firmware >> > > problem. >> > >> > It's not only about Galileo anymore. >> > >> >> Looking at the x86 kexec EFI code, it seems that it has special >> handling for the legacy SMBIOS table address, but not for the SMBIOS3 >> table address, which was introduced to accommodate SMBIOS tables >> living in memory that is not 32-bit addressable. >> >> Could anyone check whether these systems provide SMBIOS 3.0 tables, >> and whether their address gets virtually remapped at ExitBootServices? > > On Microsoft Surface 3 tablet: > > === First kernel === > > # uname -a > > (Previously reported issue on) > Linux buildroot 4.13.0+ #39 SMP Tue Sep 5 14:58:23 EEST 2017 x86_64 GNU/Linux > > (Updated today to) > Linux buildroot 5.4.0+ #2 SMP Tue Nov 26 15:36:31 EET 2019 x86_64 GNU/Linux > > # ls -l /sys/firmware/dmi/tables/ > total 0 > -r-------- 1 root root 825 Jan 21 15:41 DMI > -r-------- 1 root root 31 Jan 21 15:41 smbios_entry_point > > # od -Ax -tx1 /sys/firmware/dmi/tables/smbios_entry_point > 000000 5f 53 4d 5f 0f 1f 02 08 6a 00 00 00 00 00 00 00 > 000010 5f 44 4d 49 5f e0 39 03 00 40 5b 7b 0f 00 27 > 00001f > > # dmesg | grep -i dmi > [ 0.000000] DMI: Microsoft Corporation Surface 3/Surface 3, BIOS 1.50410.78 03/10/2015 > [ 0.403058] ACPI: Added _OSI(Linux-Lenovo-NV-HDMI-Audio) > > # dmesg | grep -i smb > [ 0.000000] efi: ESRT=0x7b7c6c98 ACPI=0x7ad5a000 ACPI 2.0=0x7ad5a000 SMBIOS=0x7b5f7d18 > [ 0.000000] SMBIOS 2.8 present. > > === kexec'ed kernel === > # uname -a > (in both cases, see above `uname -a`, the same version) > Linux buildroot 5.5.0-rc7+ #161 SMP Tue Jan 21 15:50:02 EET 2020 x86_64 GNU/Linux > > # dmidecode > # dmidecode 3.2 > Scanning /dev/mem for entry point. > # No SMBIOS nor DMI entry point found, sorry. > > # dmidecode --no-sysfs > # dmidecode 3.2 > Scanning /dev/mem for entry point. > # No SMBIOS nor DMI entry point found, sorry. This sounds like at least something of a different issue, with similar symptoms. I don't think it is fundamentally wrong to pass the location of the dmi tables in a command line option. If you can build that command line option independent of kexec and it takes practically no maintenance then it does not harm, and can be used as a debug option by others. My primary concern with your original patch is because it did not apply to any version of the kernel in Linus's git tree that it had not been tested on any code. That said let me lay some background on kexec and efi so we can have a productive conversation about how to maintain their cooperation in the long term. I am going to do this from memory so please forgive me where I get my details slightly off. EFI has two interesting calls for an operating system. SetVirtualMap ExitBootServices The law of large numbers strongly suggests that when it comes to emperical testing any interface that is not so heavily used it will fail to boot all operating systems if it doesn't work will have at least one broken implementation somewhere. A bug so bad nothing can boot means the hardware is unshippable and so will not be seen in the wild. As firmware is essentially fixed once a machine ships this means that all firmware problems have to be dealt with by the boot loader and the operating system. SetVirtualMap by design can be called only once, which is problematic when you are switching operating systems on a running system (kexec). Last I was paying attention there were also systems discovered that won't work if SetVirtualMap is not called at all. I believe the solution adopted for x86_64 was to always map EFI at the same location in the page tables and only call SetVirtualMap the first time. ExitBootSerives is similarly challenging as it can only be called once, and there are systems that get it wrong if you call it at all. Even if ExitBootServices works you can't depend on any of the boot services for the second kernel. There are two primary uses for kexec. To use the first kernel as a boot loader in which case it is desiable for everything to work after kexec is called. To use the second kernel as something to capture a crash dump in which case simply a best effor is needed and failing cleanly if something won't work properly. You are running interactive commands so I presume you are wanting to use kexec as a bootloader. I don't know where things are now but for a while was no desire to address the concerns of people using kexec by the folks implementing EFI or the folks implementing EFI support in the kernel. But that is probably how we got into a situation where efi support does not work cleanly. EFI choosing to place firwmare tables in somewhere besides their architecturally defined location does not help. I don't practically have a system with EFI so I have not personally cared to fix any of the problems. My sense is that for making EFI calls from any linux kernel should be isolated in it's own page table, so isolate as much as possible any EFI bugs from the rest of the kernel. That is probably also needed to provide a guard against speculative execution side channel attacks. I can see doing some work to get EFI functional after kexec if it isn't but at the same time I am not a fan of performing any unnecessary firmware calls. Someone sometime will implement one wrong, and it will be a headache for everyone until it is removed. By the same token I don't understand the problem with DMI not working. As I recall all the linux kernel really uses DMI for is to decide which quirks to apply. It might be better just to pass a board name string on the kernel command line, and use that string for quirk selection instead. A simple string seems like an easy to implement and use debug command line option, that has uses outside of kexec. AKA testing to see if quirks do what you expect them too. Which brings us to the question of quirks. Why are quirks important? If they are that suggests something else is wrong. Maybe that something else should be fixed. Why do those boards need the DMI information in the first place? Eric _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
