Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.
code
Clone this repository
https://tangled.org/tjh.dev/kernel
git@gordian.tjh.dev:tjh.dev/kernel
For self-hosted knots, clone URLs may differ based on your setup.
Pull Kbuild fixes from Masahiro Yamada:
- Fix section mismatch warning messages for riscv and loongarch
- Remove CONFIG_IA64 left-over from linux/export-internal.h
- Fix the location of the quotes for UIMAGE_NAME
- Fix a memory leak bug in Kconfig
* tag 'kbuild-fixes-v6.7' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild:
kconfig: fix memory leak from range properties
kbuild: Move the single quotes for image name
linux/export: clean up the IA-64 KSYM_FUNC macro
modpost: fix section mismatch message for RELA
Pull irq fix from Borislav Petkov:
- Flush the translation service tables to prevent unpredictable
behavior on non-coherent GIC devices
* tag 'irq_urgent_for_v6.7_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
irqchip/gic-v3-its: Flush ITS tables correctly in non-coherent GIC designs
Currently, sym_validate_range() duplicates the range string using
xstrdup(), which is overwritten by a subsequent sym_calc_value() call.
It results in a memory leak.
Instead, only the pointer should be copied.
Below is a test case, with a summary from Valgrind.
[Test Kconfig]
config FOO
int "foo"
range 10 20
[Test .config]
CONFIG_FOO=0
[Before]
LEAK SUMMARY:
definitely lost: 3 bytes in 1 blocks
indirectly lost: 0 bytes in 0 blocks
possibly lost: 0 bytes in 0 blocks
still reachable: 17,465 bytes in 21 blocks
suppressed: 0 bytes in 0 blocks
[After]
LEAK SUMMARY:
definitely lost: 0 bytes in 0 blocks
indirectly lost: 0 bytes in 0 blocks
possibly lost: 0 bytes in 0 blocks
still reachable: 17,462 bytes in 20 blocks
suppressed: 0 bytes in 0 blocks
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Pull x86 fixes from Borislav Petkov:
- Ignore invalid x2APIC entries in order to not waste per-CPU data
- Fix a back-to-back signals handling scenario when shadow stack is in
use
- A documentation fix
- Add Kirill as TDX maintainer
* tag 'x86_urgent_for_v6.7_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/acpi: Ignore invalid x2APIC entries
x86/shstk: Delay signal entry SSP write until after user accesses
x86/Documentation: Indent 'note::' directive for protocol version number note
MAINTAINERS: Add Intel TDX entry
In non-coherent GIC designs, the ITS tables must be flushed before writing
to the GITS_BASER<n> registers, otherwise the ITS could read dirty tables,
which results in unpredictable behavior.
Flush the tables right at the begin of its_setup_baser() to prevent that.
[ tglx: Massage changelog ]
Fixes: a8707f553884 ("irqchip/gic-v3: Add Rockchip 3588001 erratum workaround")
Suggested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Fang Xiang <fangxiang3@xiaomi.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231030083256.4345-1-fangxiang3@xiaomi.com
Add quotes where UIMAGE_NAME is used, rather than where it is defined.
This allows the UIMAGE_NAME variable to be set by the user.
Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Pull timer fix from Borislav Petkov:
- Do the push of pending hrtimers away from a CPU which is being
offlined earlier in the offlining process in order to prevent a
deadlock
* tag 'timers_urgent_for_v6.7_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
hrtimers: Push pending hrtimers away from outgoing CPU earlier
Currently, the kernel enumerates the possible CPUs by parsing both ACPI
MADT Local APIC entries and x2APIC entries. So CPUs with "valid" APIC IDs,
even if they have duplicated APIC IDs in Local APIC and x2APIC, are always
enumerated.
Below is what ACPI MADT Local APIC and x2APIC describes on an
Ivebridge-EP system,
[02Ch 0044 1] Subtable Type : 00 [Processor Local APIC]
[02Fh 0047 1] Local Apic ID : 00
...
[164h 0356 1] Subtable Type : 00 [Processor Local APIC]
[167h 0359 1] Local Apic ID : 39
[16Ch 0364 1] Subtable Type : 00 [Processor Local APIC]
[16Fh 0367 1] Local Apic ID : FF
...
[3ECh 1004 1] Subtable Type : 09 [Processor Local x2APIC]
[3F0h 1008 4] Processor x2Apic ID : 00000000
...
[B5Ch 2908 1] Subtable Type : 09 [Processor Local x2APIC]
[B60h 2912 4] Processor x2Apic ID : 00000077
As a result, kernel shows "smpboot: Allowing 168 CPUs, 120 hotplug CPUs".
And this wastes significant amount of memory for the per-cpu data.
Plus this also breaks https://lore.kernel.org/all/87edm36qqb.ffs@tglx/,
because __max_logical_packages is over-estimated by the APIC IDs in
the x2APIC entries.
According to https://uefi.org/specs/ACPI/6.5/05_ACPI_Software_Programming_Model.html#processor-local-x2apic-structure:
"[Compatibility note] On some legacy OSes, Logical processors with APIC
ID values less than 255 (whether in XAPIC or X2APIC mode) must use the
Processor Local APIC structure to convey their APIC information to OSPM,
and those processors must be declared in the DSDT using the Processor()
keyword. Logical processors with APIC ID values 255 and greater must use
the Processor Local x2APIC structure and be declared using the Device()
keyword."
Therefore prevent the registration of x2APIC entries with an APIC ID less
than 255 if the local APIC table enumerates valid APIC IDs.
[ tglx: Simplify the logic ]
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230702162802.344176-1-rui.zhang@intel.com
Pull x86 TDX updates from Dave Hansen:
"The majority of this is a rework of the assembly and C wrappers that
are used to talk to the TDX module and VMM. This is a nice cleanup in
general but is also clearing the way for using this code when Linux is
the TDX VMM.
There are also some tidbits to make TDX guests play nicer with Hyper-V
and to take advantage the hardware TSC.
Summary:
- Refactor and clean up TDX hypercall/module call infrastructure
- Handle retrying/resuming page conversion hypercalls
- Make sure to use the (shockingly) reliable TSC in TDX guests"
[ TLA reminder: TDX is "Trust Domain Extensions", Intel's guest VM
confidentiality technology ]
* tag 'x86_tdx_for_6.7' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/tdx: Mark TSC reliable
x86/tdx: Fix __noreturn build warning around __tdx_hypercall_failed()
x86/virt/tdx: Make TDX_MODULE_CALL handle SEAMCALL #UD and #GP
x86/virt/tdx: Wire up basic SEAMCALL functions
x86/tdx: Remove 'struct tdx_hypercall_args'
x86/tdx: Reimplement __tdx_hypercall() using TDX_MODULE_CALL asm
x86/tdx: Make TDX_HYPERCALL asm similar to TDX_MODULE_CALL
x86/tdx: Extend TDX_MODULE_CALL to support more TDCALL/SEAMCALL leafs
x86/tdx: Pass TDCALL/SEAMCALL input/output registers via a structure
x86/tdx: Rename __tdx_module_call() to __tdcall()
x86/tdx: Make macros of TDCALLs consistent with the spec
x86/tdx: Skip saving output regs when SEAMCALL fails with VMFailInvalid
x86/tdx: Zero out the missing RSI in TDX_HYPERCALL macro
x86/tdx: Retry partially-completed page conversion hypercalls
With commit cf8e8658100d ("arch: Remove Itanium (IA-64) architecture"),
there is no need to keep the IA-64 definition of the KSYM_FUNC macro.
Clean up the IA-64 definition of the KSYM_FUNC macro.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Pull scheduler fixes from Borislav Petkov:
- Fix virtual runtime calculation when recomputing a sched entity's
weights
- Fix wrongly rejected unprivileged poll requests to the cgroup psi
pressure files
- Make sure the load balancing is done by only one CPU
* tag 'sched_urgent_for_v6.7_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/fair: Fix the decision for load balance
sched: psi: fix unprivileged polling against cgroups
sched/eevdf: Fix vruntime adjustment on reweight
2b8272ff4a70 ("cpu/hotplug: Prevent self deadlock on CPU hot-unplug")
solved the straight forward CPU hotplug deadlock vs. the scheduler
bandwidth timer. Yu discovered a more involved variant where a task which
has a bandwidth timer started on the outgoing CPU holds a lock and then
gets throttled. If the lock required by one of the CPU hotplug callbacks
the hotplug operation deadlocks because the unthrottling timer event is not
handled on the dying CPU and can only be recovered once the control CPU
reaches the hotplug state which pulls the pending hrtimers from the dead
CPU.
Solve this by pushing the hrtimers away from the dying CPU in the dying
callbacks. Nothing can queue a hrtimer on the dying CPU at that point because
all other CPUs spin in stop_machine() with interrupts disabled and once the
operation is finished the CPU is marked offline.
Reported-by: Yu Liao <liaoyu15@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Liu Tie <liutie4@huawei.com>
Link: https://lore.kernel.org/r/87a5rphara.ffs@tglx
When a signal is being delivered, the kernel needs to make accesses to
userspace. These accesses could encounter an access error, in which case
the signal delivery itself will trigger a segfault. Usually this would
result in the kernel killing the process. But in the case of a SEGV signal
handler being configured, the failure of the first signal delivery will
result in *another* signal getting delivered. The second signal may
succeed if another thread has resolved the issue that triggered the
segfault (i.e. a well timed mprotect()/mmap()), or the second signal is
being delivered to another stack (i.e. an alt stack).
On x86, in the non-shadow stack case, all the accesses to userspace are
done before changes to the registers (in pt_regs). The operation is
aborted when an access error occurs, so although there may be writes done
for the first signal, control flow changes for the signal (regs->ip,
regs->sp, etc) are not committed until all the accesses have already
completed successfully. This means that the second signal will be
delivered as if it happened at the time of the first signal. It will
effectively replace the first aborted signal, overwriting the half-written
frame of the aborted signal. So on sigreturn from the second signal,
control flow will resume happily from the point of control flow where the
original signal was delivered.
The problem is, when shadow stack is active, the shadow stack SSP
register/MSR is updated *before* some of the userspace accesses. This
means if the earlier accesses succeed and the later ones fail, the second
signal will not be delivered at the same spot on the shadow stack as the
first one. So on sigreturn from the second signal, the SSP will be
pointing to the wrong location on the shadow stack (off by a frame).
Pengfei privately reported that while using a shadow stack enabled glibc,
the “signal06” test in the LTP test-suite hung. It turns out it is
testing the above described double signal scenario. When this test was
compiled with shadow stack, the first signal pushed a shadow stack
sigframe, then the second pushed another. When the second signal was
handled, the SSP was at the first shadow stack signal frame instead of
the original location. The test then got stuck as the #CP from the twice
incremented SSP was incorrect and generated segfaults in a loop.
Fix this by adjusting the SSP register only after any userspace accesses,
such that there can be no failures after the SSP is adjusted. Do this by
moving the shadow stack sigframe push logic to happen after all other
userspace accesses.
Note, sigreturn (as opposed to the signal delivery dealt with in this
patch) has ordering behavior that could lead to similar failures. The
ordering issues there extend beyond shadow stack to include the alt stack
restoration. Fixing that would require cross-arch changes, and the
ordering today does not cause any known test or apps breakages. So leave
it as is, for now.
[ dhansen: minor changelog/subject tweak ]
Fixes: 05e36022c054 ("x86/shstk: Handle signals for shadow stack")
Reported-by: Pengfei Xu <pengfei.xu@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Cc:stable@vger.kernel.org
Link: https://lore.kernel.org/all/20231107182251.91276-1-rick.p.edgecombe%40intel.com
Link: https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/signal/signal06.c
Pull parisc updates from Helge Deller:
"Usual fixes and updates:
- Add up to 12 nops after TLB inserts for PA8x00 CPUs as the
specification requires (Dave Anglin)
- Simplify the parisc smp_prepare_boot_cpu() code (Russell King)
- Use 64-bit little-endian values in SBA IOMMU PDIR table for AGP
Since there is upcoming support for booting a 64-bit kernel on QEMU,
some corner cases were fixed and improvements added:
- Fix 64-bit kernel crash in STI (graphics console) font setup code
which miscalculated the font start address as it gets signed vs
unsigned offsets wrong
- Support building an uncompressed Linux kernel
- Add support for soft power-off in qemu"
* tag 'parisc-for-6.7-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux:
fbdev: stifb: Make the STI next font pointer a 32-bit signed offset
parisc: Show default CPU PSW.W setting as reported by PDC
parisc/pdc: Add width field to struct pdc_model
parisc: Add nop instructions after TLB inserts
parisc: simplify smp_prepare_boot_cpu()
parisc/agp: Use 64-bit LE values in SBA IOMMU PDIR table
parisc/firmware: Use PDC constants for narrow/wide firmware
parisc: Move parisc_narrow_firmware variable to header file
parisc/power: Trivial whitespace cleanups and license update
parisc/power: Add power soft-off when running on qemu
parisc: Allow building uncompressed Linux kernel
parisc: Add some missing PDC functions and constants
parisc: sba-iommu: Fix comment when calculating IOC number
In x86 virtualization environments, including TDX, RDTSC instruction is
handled without causing a VM exit, resulting in minimal overhead and
jitters. On the other hand, other clock sources (such as HPET, ACPI
timer, APIC, etc.) necessitate VM exits to implement, resulting in more
fluctuating measurements compared to TSC. Thus, those clock sources are
not effective for calibrating TSC.
As a foundation, the host TSC is guaranteed to be invariant on any
system which enumerates TDX support.
TDX guests and the TDX module build on that foundation by enforcing:
- Virtual TSC is monotonously incrementing for any single VCPU;
- Virtual TSC values are consistent among all the TD’s VCPUs at the
level supported by the CPU:
+ VMM is required to set the same TSC_ADJUST;
+ VMM must not modify from initial value of TSC_ADJUST before
SEAMCALL;
- The frequency is determined by TD configuration:
+ Virtual TSC frequency is specified by VMM on TDH.MNG.INIT;
+ Virtual TSC starts counting from 0 at TDH.MNG.INIT;
The result is that a reliable TSC is a TDX architectural guarantee.
Use the TSC as the only reliable clock source in TD guests, bypassing
unstable calibration.
This is similar to what the kernel already does in some VMWare and
HyperV environments.
[ dhansen: changelog tweaks ]
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Erdem Aktas <erdemaktas@google.com>
Reviewed-by: Isaku Yamahata <isaku.yamahata@intel.com>
Acked-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/all/20231006144549.2633-1-kirill.shutemov%40linux.intel.com