https://lkml.org/lkml/2020/2/19/1051

…ted MC

> CONFIG_EDAC_SKX:
>
> Support for error detection and correction the Intel
> Skylake server Integrated Memory Controllers. If your
> system has non-volatile DIMMs you should also manually
> select CONFIG_ACPI_NFIT.

Fixes: #1700

libata should also support all these devices.

    Uniform Multi-Platform E-IDE driver
    ide_generic: please use "probe_mask=0x3f" module parameter for probing all legacy ISA IDE ports
    legacy IDE will be removed in 2021, please switch to libata
    Report any missing HW support to linux-ide@vger.kernel.org
    Probing IDE interface ide0...
    ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
    legacy IDE will be removed in 2021, please switch to libata
    Report any missing HW support to linux-ide@vger.kernel.org
    Probing IDE interface ide1...

Fixes: #1707

> SECURITY_LOCKDOWN_LSM
>
> Build support for an LSM that enforces a coarse kernel lockdown
> behaviour.

Do not enable it by default.

Fixes: #1710

> CONFIG_X86_X2APIC:
>
> This enables x2apic support on CPUs that have this feature.
>
> This allows 32-bit apic IDs (so it can support very large systems),
> and accesses the local apic via MSRs not via mmio.

On the Dell PowerEdge T640/04WYPY, BIOS 2.4.8 11/27/2019, Linux crashes on start-up.

    [    3.862327] ACPI: Core revision 20190816
    [    3.869551] clocksource: hpet: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 79635855245 ns
    [    3.878797] APIC: Switch to symmetric I/O mode setup
    [    3.883893] Switched APIC routing to physical flat.
    [    3.888904] ------------[ cut here ]------------
    [    3.893641] kernel BUG at arch/x86/kernel/apic/apic.c:1616!
    [    3.899347] invalid opcode: 0000 [#1] SMP NOPTI
    [    3.903990] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.4.14.mx64.317 #1
    [    3.910803] Hardware name: Dell Inc. PowerEdge T640/04WYPY, BIOS 2.4.8 11/27/2019
    [    3.918448] RIP: 0010:setup_local_APIC+0x32e/0x390
    [    3.923356] Code: 68 70 2e 01 be 00 07 01 00 bf 50 03 00 00 48 8b 40 10 e8 15 9e db 00 eb a9 be 00 04 01 00 bf 60 03 00 00 e8 04 9e db 00 eb bb <0f> 0b e8 5b 3a 00 00
    [    3.942300] RSP: 0000:ffffffff82403e88 EFLAGS: 00010246
    [    3.947641] RAX: 0000000000000000 RBX: 00000000000000ff RCX: ffffffff82454128
    [    3.955787] RDX: 0000000000000000 RSI: 00000000fffffeff RDI: 0000000000000020
    [    3.963031] RBP: ffffffffffffffff R08: 00000000000001c4 R09: 0734073407370739
    [    3.970277] R10: ffffffff82573000 R11: 0720072007730765 R12: ffffffff82a4a920
    [    3.977522] R13: 0000000000000000 R14: ffff88c07fff0e80 R15: 0000000000000000
    [    3.984766] FS:  0000000000000000(0000) GS:ffff889fffc00000(0000) knlGS:0000000000000000
    [    3.993014] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    [    3.998876] CR2: ffff88c07ffff000 CR3: 000000000240a001 CR4: 00000000000606b0
    [    4.006121] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    [    4.013365] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    [    4.020611] Call Trace:
    [    4.023184]  apic_intr_mode_init+0x1d2/0x1ec
    [    4.027573]  x86_late_time_init+0x17/0x1c
    [    4.031706]  start_kernel+0x41f/0x4d3
    [    4.035491]  secondary_startup_64+0xa4/0xb0
    [    4.039797] Modules linked in:
    [    4.042997] ---[ end trace c3629ce2e87a638c ]---
    [    4.047746] RIP: 0010:setup_local_APIC+0x32e/0x390
    [    4.052663] Code: 68 70 2e 01 be 00 07 01 00 bf 50 03 00 00 48 8b 40 10 e8 15 9e db 00 eb a9 be 00 04 01 00 bf 60 03 00 00 e8 04 9e db 00 eb bb <0f> 0b e8 5b 3a 00 00
    [    4.071617] RSP: 0000:ffffffff82403e88 EFLAGS: 00010246
    [    4.076966] RAX: 0000000000000000 RBX: 00000000000000ff RCX: ffffffff82454128
    [    4.084219] RDX: 0000000000000000 RSI: 00000000fffffeff RDI: 0000000000000020
    [    4.091475] RBP: ffffffffffffffff R08: 00000000000001c4 R09: 0734073407370739
    [    4.098738] R10: ffffffff82573000 R11: 0720072007730765 R12: ffffffff82a4a920
    [    4.106000] R13: 0000000000000000 R14: ffff88c07fff0e80 R15: 0000000000000000
    [    4.113252] FS:  0000000000000000(0000) GS:ffff889fffc00000(0000) knlGS:0000000000000000
    [    4.121509] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    [    4.127380] CR2: ffff88c07ffff000 CR3: 000000000240a001 CR4: 00000000000606b0
    [    4.134632] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    [    4.141887] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    [    4.149142] Kernel panic - not syncing: Attempted to kill the idle task!
    [    4.155968] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---

The reason is the code below in `arch/x86/kernel/apic/apic.c`.

        /*
         * Double-check whether this APIC is really registered.
         * This is meaningless in clustered apic mode, so we skip it.
         */
        BUG_ON(!apic->apic_id_registered());

With `acpi=off noapic` the panic below is shown.

    [    2.577272] Kernel panic - not syncing: BIOS has enabled x2apic but kernel doesn't support x2apic, please disable x2apic in BIOS.

With `nosmp` it also crashes at the same spot.

    [    3.705437] APIC: SMP mode deactivated
    [    3.709189] APIC: Switch to symmetric I/O mode setup in no SMP routine
    [    3.715712] ------------[ cut here ]------------
    [    3.720320] kernel BUG at arch/x86/kernel/apic/apic.c:1616!

Selecting X2APIC support in Linux fixes the crashes/panics.

Disabling x2APIC in the Dell firmware also get the Linux kernel with no
X2APIC support to boot, but some posts on the Web claim, that X2APIC is
more efficient [1].

[1]: https://serverfault.com/questions/873664/when-to-use-x2apic-mode

> CONFIG_INTEL_IOMMU:
>
> DMA remapping (DMAR) devices support enables independent address
> translations for Direct Memory Access (DMA) from devices.
> These DMA remapping devices are reported via ACPI tables
> and include PCI device scope covered by these DMA
> remapping devices.

> CONFIG_AMD_IOMMU_V2:
>
> This option enables support for the AMD IOMMUv2 features of the IOMMU
> hardware. Select this option if you want to use devices that support
> the PCI PRI and PASID interface.

The USB FTDI Single Port Serial Driver is not needed for booting, so
build it as a module instead of directly into the kernel.

Do not build the USB ZyXEL omni.net LCD Plus Driver as no users are
known. If the driver is needed, it should be built as a module.

We have such a device now, so build the USB Prolific 2303 Single Port
Serial Driver as a module as requested in the merge/pull request
comments.

[1]: #1714