tjh.dev
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.
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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 kvm fixes from Paolo Bonzini:
"Two small fixes, one of which was being worked around in selftests"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
KVM: x86: Retry page fault if MMU reload is pending and root has no sp
KVM: selftests: vmx_pmu_msrs_test: Drop tests mangling guest visible CPUIDs
KVM: x86: Drop guest CPUID check for host initiated writes to MSR_IA32_PERF_CAPABILITIES
Pull block revert from Jens Axboe:
"It turns out that the fix for not hammering on the delayed work timer
too much caused a performance regression for BFQ, so let's revert the
change for now.
I've got some ideas on how to fix it appropriately, but they should
wait for 5.17"
* tag 'block-5.16-2021-12-19' of git://git.kernel.dk/linux-block:
Revert "block: reduce kblockd_mod_delayed_work_on() CPU consumption"
Play nice with a NULL shadow page when checking for an obsolete root in
the page fault handler by flagging the page fault as stale if there's no
shadow page associated with the root and KVM_REQ_MMU_RELOAD is pending.
Invalidating memslots, which is the only case where _all_ roots need to
be reloaded, requests all vCPUs to reload their MMUs while holding
mmu_lock for lock.
The "special" roots, e.g. pae_root when KVM uses PAE paging, are not
backed by a shadow page. Running with TDP disabled or with nested NPT
explodes spectaculary due to dereferencing a NULL shadow page pointer.
Skip the KVM_REQ_MMU_RELOAD check if there is a valid shadow page for the
root. Zapping shadow pages in response to guest activity, e.g. when the
guest frees a PGD, can trigger KVM_REQ_MMU_RELOAD even if the current
vCPU isn't using the affected root. I.e. KVM_REQ_MMU_RELOAD can be seen
with a completely valid root shadow page. This is a bit of a moot point
as KVM currently unloads all roots on KVM_REQ_MMU_RELOAD, but that will
be cleaned up in the future.
Fixes: a955cad84cda ("KVM: x86/mmu: Retry page fault if root is invalidated by memslot update")
Cc: stable@vger.kernel.org
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211209060552.2956723-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Pull irq fixes from Borislav Petkov:
- Clear the PCI_MSIX_FLAGS_MASKALL bit too on the error path so that it
is restored to its reset state
- Mask MSI-X vectors late on the init path in order to handle
out-of-spec Marvell NVME devices which apparently look at the MSI-X
mask even when MSI-X is disabled
* tag 'irq_urgent_for_v5.16_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
PCI/MSI: Clear PCI_MSIX_FLAGS_MASKALL on error
PCI/MSI: Mask MSI-X vectors only on success
This reverts commit cb2ac2912a9ca7d3d26291c511939a41361d2d83.
Alex and the kernel test robot report that this causes a significant
performance regression with BFQ. I can reproduce that result, so let's
revert this one as we're close to -rc6 and we there's no point in trying
to rush a fix.
Link: https://lore.kernel.org/linux-block/1639853092.524jxfaem2.none@localhost/
Link: https://lore.kernel.org/lkml/20211219141852.GH14057@xsang-OptiPlex-9020/
Reported-by: Alex Xu (Hello71) <alex_y_xu@yahoo.ca>
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Host initiated writes to MSR_IA32_PERF_CAPABILITIES should not depend
on guest visible CPUIDs and (incorrect) KVM logic implementing it is
about to change. Also, KVM_SET_CPUID{,2} after KVM_RUN is now forbidden
and causes test to fail.
Reported-by: kernel test robot <oliver.sang@intel.com>
Fixes: feb627e8d6f6 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20211216165213.338923-2-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Pull timer fix from Borislav Petkov:
- Make sure the CLOCK_REALTIME to CLOCK_MONOTONIC offset is never
positive
* tag 'timers_urgent_for_v5.16_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
timekeeping: Really make sure wall_to_monotonic isn't positive
PCI_MSIX_FLAGS_MASKALL is set in the MSI-X control register at MSI-X
interrupt setup time. It's cleared on success, but the error handling path
only clears the PCI_MSIX_FLAGS_ENABLE bit.
That's incorrect as the reset state of the PCI_MSIX_FLAGS_MASKALL bit is
zero. That can be observed via lspci:
Capabilities: [b0] MSI-X: Enable- Count=67 Masked+
Clear the bit in the error path to restore the reset state.
Fixes: 438553958ba1 ("PCI/MSI: Enable and mask MSI-X early")
Reported-by: Stefan Roese <sr@denx.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Stefan Roese <sr@denx.de>
Cc: linux-pci@vger.kernel.org
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Marek Vasut <marex@denx.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/87tufevoqx.ffs@tglx
Commit 0259d4498ba4 ("bcache: move calc_cached_dev_sectors to proper
place on backing device detach") tries to fix calc_cached_dev_sectors
when bcache device detaches, but now we have:
cached_dev_detach_finish
...
bcache_device_detach(&dc->disk);
...
closure_put(&d->c->caching);
d->c = NULL; [*explicitly set dc->disk.c to NULL*]
list_move(&dc->list, &uncached_devices);
calc_cached_dev_sectors(dc->disk.c); [*passing a NULL pointer*]
...
Upper codeflows shows how bug happens, this patch fix the problem by
caching dc->disk.c beforehand, and cache_set won't be freed under us
because c->caching closure at least holds a reference count and closure
callback __cache_set_unregister only being called by bch_cache_set_stop
which using closure_queue(&c->caching), that means c->caching closure
callback for destroying cache_set won't be trigger by previous
closure_put(&d->c->caching).
So at this stage(while cached_dev_detach_finish is calling) it's safe to
access cache_set dc->disk.c.
Fixes: 0259d4498ba4 ("bcache: move calc_cached_dev_sectors to proper place on backing device detach")
Signed-off-by: Lin Feng <linf@wangsu.com>
Signed-off-by: Coly Li <colyli@suse.de>
Link: https://lore.kernel.org/r/20211112053629.3437-2-colyli@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The ability to write to MSR_IA32_PERF_CAPABILITIES from the host should
not depend on guest visible CPUID entries, even if just to allow
creating/restoring guest MSRs and CPUIDs in any sequence.
Fixes: 27461da31089 ("KVM: x86/pmu: Support full width counting")
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20211216165213.338923-3-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Pull locking fix from Borislav Petkov:
- Fix the rtmutex condition checking when the optimistic spinning of a
waiter needs to be terminated
* tag 'locking_urgent_for_v5.16_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
locking/rtmutex: Fix incorrect condition in rtmutex_spin_on_owner()
Even after commit e1d7ba873555 ("time: Always make sure wall_to_monotonic
isn't positive") it is still possible to make wall_to_monotonic positive
by running the following code:
int main(void)
{
struct timespec time;
clock_gettime(CLOCK_MONOTONIC, &time);
time.tv_nsec = 0;
clock_settime(CLOCK_REALTIME, &time);
return 0;
}
The reason is that the second parameter of timespec64_compare(), ts_delta,
may be unnormalized because the delta is calculated with an open coded
substraction which causes the comparison of tv_sec to yield the wrong
result:
wall_to_monotonic = { .tv_sec = -10, .tv_nsec = 900000000 }
ts_delta = { .tv_sec = -9, .tv_nsec = -900000000 }
That makes timespec64_compare() claim that wall_to_monotonic < ts_delta,
but actually the result should be wall_to_monotonic > ts_delta.
After normalization, the result of timespec64_compare() is correct because
the tv_sec comparison is not longer misleading:
wall_to_monotonic = { .tv_sec = -10, .tv_nsec = 900000000 }
ts_delta = { .tv_sec = -10, .tv_nsec = 100000000 }
Use timespec64_sub() to ensure that ts_delta is normalized, which fixes the
issue.
Fixes: e1d7ba873555 ("time: Always make sure wall_to_monotonic isn't positive")
Signed-off-by: Yu Liao <liaoyu15@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211213135727.1656662-1-liaoyu15@huawei.com
Masking all unused MSI-X entries is done to ensure that a crash kernel
starts from a clean slate, which correponds to the reset state of the
device as defined in the PCI-E specificion 3.0 and later:
Vector Control for MSI-X Table Entries
--------------------------------------
"00: Mask bit: When this bit is set, the function is prohibited from
sending a message using this MSI-X Table entry.
...
This bit’s state after reset is 1 (entry is masked)."
A Marvell NVME device fails to deliver MSI interrupts after trying to
enable MSI-X interrupts due to that masking. It seems to take the MSI-X
mask bits into account even when MSI-X is disabled.
While not specification compliant, this can be cured by moving the masking
into the success path, so that the MSI-X table entries stay in device reset
state when the MSI-X setup fails.
[ tglx: Move it into the success path, add comment and amend changelog ]
Fixes: aa8092c1d1f1 ("PCI/MSI: Mask all unused MSI-X entries")
Signed-off-by: Stefan Roese <sr@denx.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-pci@vger.kernel.org
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Marek Vasut <marex@denx.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211210161025.3287927-1-sr@denx.de
README