The AMD side of the loader issues the microcode revision for each
logical thread on the system, which can become really noisy on huge
machines. And doing that doesn't make a whole lot of sense - the
microcode revision is already in /proc/cpuinfo.
So in case one is interested in the theoretical support of mixed silicon
steppings on AMD, one can check there.
What is also missing on the AMD side - something which people have
requested before - is showing the microcode revision the CPU had
*before* the early update.
So abstract that up in the main code and have the BSP on each vendor
provide those revision numbers.
Then, dump them only once on driver init.
On Intel, do not dump the patch date - it is not needed.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/CAHk-=wg=%2B8rceshMkB4VnKxmRccVLtBLPBawnewZuuqyx5U=3A@mail.gmail.com
Applying microcode late can be fatal for the running kernel when the
update changes functionality which is in use already in a non-compatible
way, e.g. by removing a CPUID bit.
There is no way for admins which do not have access to the vendors deep
technical support to decide whether late loading of such a microcode is
safe or not.
Intel has added a new field to the microcode header which tells the
minimal microcode revision which is required to be active in the CPU in
order to be safe.
Provide infrastructure for handling this in the core code and a command
line switch which allows to enforce it.
If the update is considered safe the kernel is not tainted and the annoying
warning message not emitted. If it's enforced and the currently loaded
microcode revision is not safe for late loading then the load is aborted.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231017211724.079611170@linutronix.de
Offline CPUs need to be parked in a safe loop when microcode update is
in progress on the primary CPU. Currently, offline CPUs are parked in
mwait_play_dead(), and for Intel CPUs, its not a safe instruction,
because the MWAIT instruction can be patched in the new microcode update
that can cause instability.
- Add a new microcode state 'UCODE_OFFLINE' to report status on per-CPU
basis.
- Force NMI on the offline CPUs.
Wake up offline CPUs while the update is in progress and then return
them back to mwait_play_dead() after microcode update is complete.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231002115903.660850472@linutronix.de
stop_machine() does not prevent the spin-waiting sibling from handling
an NMI, which is obviously violating the whole concept of rendezvous.
Implement a static branch right in the beginning of the NMI handler
which is nopped out except when enabled by the late loading mechanism.
The late loader enables the static branch before stop_machine() is
invoked. Each CPU has an nmi_enable in its control structure which
indicates whether the CPU should go into the update routine.
This is required to bridge the gap between enabling the branch and
actually being at the point where it is required to enter the loader
wait loop.
Each CPU which arrives in the stopper thread function sets that flag and
issues a self NMI right after that. If the NMI function sees the flag
clear, it returns. If it's set it clears the flag and enters the
rendezvous.
This is safe against a real NMI which hits in between setting the flag
and sending the NMI to itself. The real NMI will be swallowed by the
microcode update and the self NMI will then let stuff continue.
Otherwise this would end up with a spurious NMI.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231002115903.489900814@linutronix.de
The microcode rendezvous is purely acting on global state, which does
not allow to analyze fails in a coherent way.
Introduce per CPU state where the results are written into, which allows to
analyze the return codes of the individual CPUs.
Initialize the state when walking the cpu_present_mask in the online
check to avoid another for_each_cpu() loop.
Enhance the result print out with that.
The structure is intentionally named ucode_ctrl as it will gain control
fields in subsequent changes.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231017211723.632681010@linutronix.de
On CPUs where microcode loading is not NMI-safe the SMT siblings which
are parked in one of the play_dead() variants still react to NMIs.
So if an NMI hits while the primary thread updates the microcode the
resulting behaviour is undefined. The default play_dead() implementation on
modern CPUs is using MWAIT which is not guaranteed to be safe against
a microcode update which affects MWAIT.
Take the cpus_booted_once_mask into account to detect this case and
refuse to load late if the vendor specific driver does not advertise
that late loading is NMI safe.
AMD stated that this is safe, so mark the AMD driver accordingly.
This requirement will be partially lifted in later changes.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231002115903.087472735@linutronix.de
Get rid of the initrd_gone hack which was required to keep
find_microcode_in_initrd() functional after init.
As find_microcode_in_initrd() is now only used during init, mark it
accordingly.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231017211723.298854846@linutronix.de
Now that the microcode cache is initialized before the APs are brought
up, there is no point in scanning builtin/initrd microcode during AP
loading.
Convert the AP loader to utilize the cache, which in turn makes the CPU
hotplug callback which applies the microcode after initrd/builtin is
gone, obsolete as the early loading during late hotplug operations
including the resume path depends now only on the cache.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231017211723.243426023@linutronix.de
There are situations where the late microcode is loaded into memory but
is not applied:
1) The rendezvous fails
2) The microcode is rejected by the CPUs
If any of this happens then the pointer which was updated at firmware
load time is stale and subsequent CPU hotplug operations either fail to
update or create inconsistent microcode state.
Save the loaded microcode in a separate pointer before the late load is
attempted and when successful, update the hotplug pointer accordingly
via a new microcode_ops callback.
Remove the pointless fallback in the loader to a microcode pointer which
is never populated.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231002115902.505491309@linutronix.de
The early loading code is overly complicated:
- It scans the builtin/initrd for microcode not only on the BSP, but also
on all APs during early boot and then later in the boot process it
scans again to duplicate and save the microcode before initrd goes
away.
That's a pointless exercise because this can be simply done before
bringing up the APs when the memory allocator is up and running.
- Saving the microcode from within the scan loop is completely
non-obvious and a left over of the microcode cache.
This can be done at the call site now which makes it obvious.
Rework the code so that only the BSP scans the builtin/initrd microcode
once during early boot and save it away in an early initcall for later
use.
[ bp: Test and fold in a fix from tglx ontop which handles the need to
distinguish what save_microcode() does depending on when it is
called:
- when on the BSP during early load, it needs to find a newer
revision than the one currently loaded on the BSP
- later, before SMP init, it still runs on the BSP and gets the BSP
revision just loaded and uses that revision to know which patch
to save for the APs. For that it needs to find the exact one as
on the BSP.
]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231017211722.629085215@linutronix.de
Mixed steppings aren't supported on Intel CPUs. Only one microcode patch
is required for the entire system. The caching of microcode blobs which
match the family and model is therefore pointless and in fact is
dysfunctional as CPU hotplug updates use only a single microcode blob,
i.e. the one where *intel_ucode_patch points to.
Remove the microcode cache and make it an AMD local feature.
[ tglx:
- save only at the end. Otherwise random microcode ends up in the
pointer for early loading
- free the ucode patch pointer in save_microcode_patch() only
after kmemdup() has succeeded, as reported by Andrew Cooper ]
Originally-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231017211722.404362809@linutronix.de
32-bit loads microcode before paging is enabled. The commit which
introduced that has zero justification in the changelog. The cover
letter has slightly more content, but it does not give any technical
justification either:
"The problem in current microcode loading method is that we load a
microcode way, way too late; ideally we should load it before turning
paging on. This may only be practical on 32 bits since we can't get
to 64-bit mode without paging on, but we should still do it as early
as at all possible."
Handwaving word salad with zero technical content.
Someone claimed in an offlist conversation that this is required for
curing the ATOM erratum AAE44/AAF40/AAG38/AAH41. That erratum requires
an microcode update in order to make the usage of PSE safe. But during
early boot, PSE is completely irrelevant and it is evaluated way later.
Neither is it relevant for the AP on single core HT enabled CPUs as the
microcode loading on the AP is not doing anything.
On dual core CPUs there is a theoretical problem if a split of an
executable large page between enabling paging including PSE and loading
the microcode happens. But that's only theoretical, it's practically
irrelevant because the affected dual core CPUs are 64bit enabled and
therefore have paging and PSE enabled before loading the microcode on
the second core. So why would it work on 64-bit but not on 32-bit?
The erratum:
"AAG38 Code Fetch May Occur to Incorrect Address After a Large Page is
Split Into 4-Kbyte Pages
Problem: If software clears the PS (page size) bit in a present PDE
(page directory entry), that will cause linear addresses mapped through
this PDE to use 4-KByte pages instead of using a large page after old
TLB entries are invalidated. Due to this erratum, if a code fetch uses
this PDE before the TLB entry for the large page is invalidated then it
may fetch from a different physical address than specified by either the
old large page translation or the new 4-KByte page translation. This
erratum may also cause speculative code fetches from incorrect addresses."
The practical relevance for this is exactly zero because there is no
splitting of large text pages during early boot-time, i.e. between paging
enable and microcode loading, and neither during CPU hotplug.
IOW, this load microcode before paging enable is yet another voodoo
programming solution in search of a problem. What's worse is that it causes
at least two serious problems:
1) When stackprotector is enabled, the microcode loader code has the
stackprotector mechanics enabled. The read from the per CPU variable
__stack_chk_guard is always accessing the virtual address either
directly on UP or via %fs on SMP. In physical address mode this
results in an access to memory above 3GB. So this works by chance as
the hardware returns the same value when there is no RAM at this
physical address. When there is RAM populated above 3G then the read
is by chance the same as nothing changes that memory during the very
early boot stage. That's not necessarily true during runtime CPU
hotplug.
2) When function tracing is enabled, the relevant microcode loader
functions and the functions invoked from there will call into the
tracing code and evaluate global and per CPU variables in physical
address mode. What could potentially go wrong?
Cure this and move the microcode loading after the early paging enable, use
the new temporary initrd mapping and remove the gunk in the microcode
loader which is required to handle physical address mode.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231017211722.348298216@linutronix.de
Commit e6bcfdd75d ("x86/microcode: Hide the config knob") removed the
MICROCODE_AMD config, but left some references in defconfigs and comments,
that have no effect on any kernel build around.
Clean up those remaining config references. No functional change.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230825141226.13566-1-lukas.bulwahn@gmail.com
There is no reason to expose all of this globally. Move everything which is
not required outside of the microcode specific code to local header files
and into the respective source files.
No functional change.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230812195727.952876381@linutronix.de
