Re: [PATCH v1 2/2] firmware: dmi_scan: Pass dmi_entry_point to kexec'ed kernel

[Andy Shevchenko]

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:
> > > >> Ccing efi people.
> > > >>
> > > >> On 12/16/16 at 02:33pm, Jean Delvare wrote:
> > > >> > On Fri, 16 Dec 2016 14:18:58 +0200, Andy Shevchenko wrote:
> > > >> > > On Fri, 2016-12-16 at 10:32 +0800, Dave Young wrote:
> > > >> > > > On 12/15/16 at 12:28pm, Jean Delvare wrote:
> > > >> > > > > I am no kexec expert but this confuses me. Shouldn't the second
> > > >> > > > > kernel have access to the EFI systab as the first kernel does? It
> > > >> > > > > includes many more pointers than just ACPI and DMI tables, and it
> > > >> > > > > would seem inconvenient to have to pass all these addresses
> > > >> > > > > individually explicitly.
> > > >> > > >
> > > >> > > > Yes, in modern linux kernel, kexec has the support for EFI, I think it
> > > >> > > > should work naturally at least in x86_64.
> > > >> > >
> > > >> > > Thanks for this good news!
> > > >> > >
> > > >> > > Unfortunately Intel Galileo is 32-bit platform.
> > > >> >
> > > >> > If it was done for X86_64 then maybe it can be generalized to X86?
> > > >>
> > > >> For X86_64, we have a new way for efi runtime memmory mapping, in i386
> > > >> code it still use old ioremap way. It is impossible to use same way as
> > > >> the X86_64 since the virtual address space is limited.
> > > >>
> > > >> But maybe for 32bit, kexec kernel can run in physical mode, but I'm not
> > > >> sure, I would suggest Andy to do a test first with efi=noruntime for
> > > >> kexec 2nd kernel.
> > > >
> > > > Guys, it was quite a long no hear from you. As I told you the proposed work
> > > > around didn't help. Today I found that Microsoft Surface 3 also affected
> > > > by this.
> > > >
> > > > 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?

Can you tell how to do this and I will try to get information?

-- 
With Best Regards,
Andy Shevchenko