MFC after:      2 weeks

When rolling back a dataset, ZFS has to purge file data resident in the
system page cache.  To do this, it loops over all vnodes for the
mountpoint and calls vn_pages_remove() to purge pages associated with
the vnode's VM object.  Each page is thus exclusively busied while the
dataset's teardown write lock is held.

When handling a page fault on a mapped ZFS file, FreeBSD's page fault
handler busies newly allocated pages and then uses VOP_GETPAGES to fill
them.  The ZFS getpages VOP acquires the teardown read lock with vnode
pages already busied.  This represents a lock order reversal which can
lead to deadlock.

To break the deadlock, observe that zfs_rezget() need only purge those
pages marked valid, and that pages busied by the page fault handler are,
by definition, invalid.  Furthermore, ZFS pages always transition from
invalid to valid with the teardown lock held, and ZFS never creates
partially valid pages.  Thus, zfs_rezget() can use the new
vn_pages_remove_valid() to skip over pages busied by the fault handler.

PR:		258208
Tested by:	pho
Reviewed by:	avg, sef, kib
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D32931

Both rctl and used xargs utility live in /usr/bin
so add REQUIRE: FILESYSTEMS

Reported by:	Peter <pmc@citylink.dinoex.sub.org>
MFC after:	3 days

This reverts commit 9ef7df022a46 ("hyperv: Register hyperv_timecounter
later during boot") and adds a comment explaining why the timecounter
needs to be registered as early as it is.

PR:		259878
Fixes:	9ef7df022a46 ("hyperv: Register hyperv_timecounter later during boot")
Reviewed by:	kib
MFC after:	3 days
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D33014

Hyper-V wants to register its MSR-based timecounter during
SI_SUB_HYPERVISOR, before SI_SUB_LOCK, since an emulated 8254 may not be
available for DELAY().  So we cannot use MTX_SYSINIT to initialize the
timecounter lock.

PR:		259878
Reviewed by:	kib
MFC after:	3 days
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D33014

MFC after:	1 week
Sponsored by:	Rubicon Communications, LLC ("Netgate")

Add a boolean parameter to minidumpsys(), to indicate a live dump. When
requested, take a snapshot of important global state, and pass this to
the machine-dependent minidump function. For now this includes the
kernel message buffer, and the bitset of pages to be dumped. Beyond
this, we don't take much action to protect the integrity of the dump
from changes in the running system.

A new function msgbuf_duplicate() is added for snapshotting the message
buffer. msgbuf_copy() is insufficient for this purpose since it marks
any new characters it finds as read.

For now, nothing can actually trigger a live minidump. A future patch
will add the mechanism for this. For simplicity and safety, live dumps
are disallowed for mips.

Reviewed by:	markj, jhb
MFC after:	2 weeks
Sponsored by:	Juniper Networks, Inc.
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D31993

When constructing the set of dumpable pages, use the bitset provided by
the state argument, rather than assuming vm_page_dump invariably. For
normal kernel minidumps this will be a pointer to vm_page_dump, but when
dumping the live system it will not.

To do this, the functions in vm_dumpset.h are extended to accept the
desired bitset as an argument. Note that this provided bitset is assumed
to be derived from vm_page_dump, and therefore has the same size.

Reviewed by:	kib, markj, jhb
MFC after:	2 weeks
Sponsored by:	Juniper Networks, Inc.
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D31992

Don't assume we are dumping the global message buffer, but use the one
provided by the state argument. While here, drop superfluous
cast to char *.

Reviewed by:	markj, jhb
MFC after:	2 weeks
Sponsored by:	Juniper Networks, Inc.
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D31991

During a live dump, we may race with updates to the kernel page tables.
This is generally okay; we accept that the state of the system while
dumping may be somewhat inconsistent with its state when the dump was
invoked. However, when walking the kernel page tables, it is important
that we load each PDE/PTE only once while operating on it. Otherwise, it
is possible to have the relevant PTE change underneath us. For example,
after checking the valid bit, but before reading the physical address.

Convert the loads to atomics, and add some validation around the
physical addresses, to ensure that we do not try to dump a non-existent
or non-canonical physical address.

Similarly, don't read kernel_vm_end more than once, on the off chance
that pmap_growkernel() is called between the two page table walks.

Reviewed by:	kib, markj
MFC after:	2 weeks
Sponsored by:	Juniper Networks, Inc.
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D31990

It is useful for quickly checking an address against the DMAP region.
These definitions exist already on arm64 and riscv.

Reviewed by:	kib, markj
MFC after:	3 days
Sponsored by:	Juniper Networks, Inc.
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D32962

The minidump code is written assuming that certain global state will not
change, and rightly so, since it executes from a kernel debugger
context. In order to support taking minidumps of a live system, we
should allow copies of relevant global state that is likely to change to
be passed as parameters to the minidumpsys() function.

This patch does the work of parameterizing this function, by adding a
struct minidumpstate argument. For now, this struct allows for copies of
the kernel message buffer, and the bitset that tracks which pages should
be dumped (vm_page_dump). Follow-up changes will actually make use of
these arguments.

Notably, dump_avail[] does not need a snapshot, since it is not expected
to change after system initialization.

The existing minidumpsys() definitions are renamed, and a thin MI
wrapper is added to kern_dump.c, which handles the construction of
the state struct. Thus, calling minidumpsys() remains as simple as
before.

Reviewed by:	kib, markj, jhb
Sponsored by:	Juniper Networks, Inc.
Sponsored by:	Klara, Inc.
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D31989

-s /debuging/debugging/

MFC after:	3 days