Commit Graph

3167 Commits

Author SHA1 Message Date
Justin Hibbits
69cea06f34 powerpc/booke64: Align initial stack setting to match that of aim64's
Clang9/LLD9 appears to get quite confused with the instruction stream used
to obtain the tmpstack pointer, almost as though it thinks this is a C
function, so tries to optimize it.  Since the AIM64 method doesn't use the
TOC to obtain the tmpstack, just follow that model, and lld won't get
confused.

Reported by:	bdragon
MFC after:	2 weeks
2019-09-28 03:33:07 +00:00
Konstantin Belousov
df08823d07 Improve MD page fault handlers.
Centralize calculation of signal and ucode delivered on unhandled page
fault in new function vm_fault_trap().  MD trap_pfault() now almost
always uses the signal numbers and error codes calculated in
consistent MI way.

This introduces the protection fault compatibility sysctls to all
non-x86 architectures which did not have that bug, but apparently they
were already much more wrong in selecting delivered signals on
protection violations.

Change the delivered signal for accesses to mapped area after the
backing object was truncated.  According to POSIX description for
mmap(2):
   The system shall always zero-fill any partial page at the end of an
   object. Further, the system shall never write out any modified
   portions of the last page of an object which are beyond its
   end. References within the address range starting at pa and
   continuing for len bytes to whole pages following the end of an
   object shall result in delivery of a SIGBUS signal.

   An implementation may generate SIGBUS signals when a reference
   would cause an error in the mapped object, such as out-of-space
   condition.
Adjust according to the description, keeping the existing
compatibility code for SIGSEGV/SIGBUS on protection failures.

For situations where kernel cannot handle page fault due to resource
limit enforcement, SIGBUS with a new error code BUS_OBJERR is
delivered.  Also, provide a new error code SEGV_PKUERR for SIGSEGV on
amd64 due to protection key access violation.

vm_fault_hold() is renamed to vm_fault().  Fixed some nits in
trap_pfault()s like mis-interpreting Mach errors as errnos.  Removed
unneeded truncations of the fault addresses reported by hardware.

PR:	211924
Reviewed by:	alc
Discussed with:	jilles, markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D21566
2019-09-27 18:43:36 +00:00
Mark Johnston
b119329d81 Complete the removal of the "wire_count" field from struct vm_page.
Convert all remaining references to that field to "ref_count" and update
comments accordingly.  No functional change intended.

Reviewed by:	alc, kib
Sponsored by:	Intel, Netflix
Differential Revision:	https://reviews.freebsd.org/D21768
2019-09-25 16:11:35 +00:00
Justin Hibbits
e44ed9d3d4 powerpc/atomic: Follow recommendations on atomic primitive comparisons
Both IBM and Freescale programming examples presume the cmpset operands will
favor equal, and pessimize the non-equal case instead.  Do the same for
atomic_cmpset_* and atomic_fcmpset_*.  This slightly pessimizes the failure
case, in favor of the success case.

MFC after:	3 weeks
2019-09-25 01:39:58 +00:00
Justin Hibbits
0cfa351ec5 powerpc: Allocate DPCPU block from domain-local memory
This should improve NUMA scalability a little, by binding to the CPU's NUMA
domain.  This matches what's done on amd64.
2019-09-25 01:23:08 +00:00
Mark Johnston
e8bcf6966b Revert r352406, which contained changes I didn't intend to commit. 2019-09-16 15:04:45 +00:00
Mark Johnston
41fd4b9422 Fix a couple of nits in r352110.
- Remove a dead variable from the amd64 pmap_extract_and_hold().
- Fix grammar in the vm_page_wire man page.

Reported by:	alc
Reviewed by:	alc, kib
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D21639
2019-09-16 15:03:12 +00:00
Justin Hibbits
1c56203bcf powerpc64/powernv: Add opal NVRAM driver for PowerNV systems
Add a very basic NVRAM driver for OPAL which can be used by the IBM
powerpc-utils nvram utility, not to be confused with the base nvram utility,
which only operates on powermac_nvram.

The IBM utility handles all partitions itself, treating the nvram device as
a plain store.

An alternative would be to manage partitions in the kernel, and augment the
base nvram utility to deal with different backing stores, but that
complicates the driver significantly.  Instead, present the same interface
IBM's utlity expects, and we get the usage for free.

Tested by:	bdragon
2019-09-14 03:30:34 +00:00
Mark Johnston
fee2a2fa39 Change synchonization rules for vm_page reference counting.
There are several mechanisms by which a vm_page reference is held,
preventing the page from being freed back to the page allocator.  In
particular, holding the page's object lock is sufficient to prevent the
page from being freed; holding the busy lock or a wiring is sufficent as
well.  These references are protected by the page lock, which must
therefore be acquired for many per-page operations.  This results in
false sharing since the page locks are external to the vm_page
structures themselves and each lock protects multiple structures.

Transition to using an atomically updated per-page reference counter.
The object's reference is counted using a flag bit in the counter.  A
second flag bit is used to atomically block new references via
pmap_extract_and_hold() while removing managed mappings of a page.
Thus, the reference count of a page is guaranteed not to increase if the
page is unbusied, unmapped, and the object's write lock is held.  As
a consequence of this, the page lock no longer protects a page's
identity; operations which move pages between objects are now
synchronized solely by the objects' locks.

The vm_page_wire() and vm_page_unwire() KPIs are changed.  The former
requires that either the object lock or the busy lock is held.  The
latter no longer has a return value and may free the page if it releases
the last reference to that page.  vm_page_unwire_noq() behaves the same
as before; the caller is responsible for checking its return value and
freeing or enqueuing the page as appropriate.  vm_page_wire_mapped() is
introduced for use in pmap_extract_and_hold().  It fails if the page is
concurrently being unmapped, typically triggering a fallback to the
fault handler.  vm_page_wire() no longer requires the page lock and
vm_page_unwire() now internally acquires the page lock when releasing
the last wiring of a page (since the page lock still protects a page's
queue state).  In particular, synchronization details are no longer
leaked into the caller.

The change excises the page lock from several frequently executed code
paths.  In particular, vm_object_terminate() no longer bounces between
page locks as it releases an object's pages, and direct I/O and
sendfile(SF_NOCACHE) completions no longer require the page lock.  In
these latter cases we now get linear scalability in the common scenario
where different threads are operating on different files.

__FreeBSD_version is bumped.  The DRM ports have been updated to
accomodate the KPI changes.

Reviewed by:	jeff (earlier version)
Tested by:	gallatin (earlier version), pho
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D20486
2019-09-09 21:32:42 +00:00
Justin Hibbits
e0b5c15c54 powerpc64/pmap: Fix a WITNESS error in alloc_pvo_entry()
We only call alloc_pvo_entry() with M_WAITOK from one location.  However,
this can be called while holding nonsleepable locks.  Rather than passing
M_WAITOK down, use vm_wait() and loop.
2019-09-06 03:02:12 +00:00
Justin Hibbits
197a7e48c9 powerpc64/pmap: Simplify the code path for moea64_pte_replace_native()
Summary:
MOEA64_PTE_REPLACE() is called often with the pmap lock held, and
sometimes with the page pv lock held.  The less work done while holding
a lock, the better.  Since we are intending to replace the same PTE
(same hash index), we don't need to recalculate anything, just flat
replace the PTE.  This cuts more than 200 instructions off the
invalidating code path.  In addition, we don't need to replace a PTE
that's not occupied by this PVO.

Reviewed by:	luporl
Differential Revision:	https://reviews.freebsd.org/D21515
2019-09-06 02:45:46 +00:00
Konstantin Belousov
a2a0f90654 Centralize __pcpu definitions.
Many extern struct pcpu <something>__pcpu declarations were
copied/pasted in sources.  The issue is that the definition is MD, but
it cannot be provided by machine/pcpu.h due to actual struct pcpu
defined in sys/pcpu.h later than the inclusion of machine/pcpu.h.
This forced the copying when other code needed direct access to
__pcpu.  There is no way around it, due to machine/pcpu.h supplying
part of struct pcpu fields.

To work around the problem, add a new machine/pcpu_aux.h header, which
should fill any needed MD definitions after struct pcpu definition is
completed. This allows to remove copies of __pcpu spread around the
source.  Also on x86 it makes it possible to remove work arounds like
OFFSETOF_CURTHREAD or clang specific warnings supressions.

Reported and tested by:	lwhsu, bcran
Reviewed by:	imp, markj (previous version)
Discussed with:	jhb
Sponsored by:	The FreeBSD Foundation
Differential revision:	https://reviews.freebsd.org/D21418
2019-08-29 07:25:27 +00:00
Justin Hibbits
7038069e9c Revert a part of r350883 that should never have gone in
The wire_count change is not part of the unification, and doesn't even make
sense.

Reported by:	markj
2019-08-27 14:04:32 +00:00
Justin Hibbits
8da08d5123 powerpc/booke: Clean up pmap a little for 64-bit
64-bit Book-E pmap doesn't need copy and zero bounce pages, nor the mutex.
Don't initialize them or reserve space for them.
2019-08-25 20:11:35 +00:00
Justin Hibbits
e7f2151c75 powerpc/booke: Use the DMAP if possible in pmap_map()
This avoids unnecessary TLB usage for statically mapped regions, such as
vm_page_array.
2019-08-25 20:08:48 +00:00
Warner Losh
7d65d42046 Fix bogusly declared WERRORs in kernel build
Many arm kernel configs bogusly specified WERROR=-Werror. There's no
reason for this because the default is that and there's no reason to
override. These date from a time when we needed to add additional
warning->error suppression. They are obsolete and were cut and paste
propagated from file to file.

Comment out all the WERROR=.... lines in powerpc. They aren't bogus,
but were appropriate for the old defaults for gcc4.2.1. Now that we've
made the policy decision to suppress -Werror by default on these
platforms, it is appropriate to comment these out. People wishing to
fix these errors can still un-comment them out, or say WERROR=-Werror
on the command line.

Fix two instances (cut and paste propagation) of hard-coded -Werror
in x86 code. Replace with ${WERROR} instead. This is a no-op change
except for people who build WERROR=-Wno-error :).

This should fix tinderbox / CI breakage.
2019-08-25 19:39:31 +00:00
Justin Hibbits
6793e5b23d powerpc: Link Book-E kernels at the same address as AIM kernels
Summary:
Reduce the diff between AIM and Book-E even more.  This also cleans up
vmparam.h significantly.

Reviewed by:	luporl
Differential Revision:	https://reviews.freebsd.org/D21301
2019-08-20 01:26:02 +00:00
Jeff Roberson
2194393787 Move phys_avail definition into MI code. It is consumed in the MI layer and
doing so adds more flexibility with less redundant code.

Reviewed by:	jhb, markj, kib
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D21250
2019-08-16 00:45:14 +00:00
Justin Hibbits
141a0ab012 powerpc/pmap: Enable UMA_MD_SMALL_ALLOC for 64-bit booke
The only thing blocking UMA_MD_SMALL_ALLOC from working on 64-bit booke
powerpc was a missing check in pmap_kextract().  Adding DMAP handling into
pmap_kextract(), we can now use UMA_MD_SMALL_ALLOC.  This should improve
performance and stability a bit, since DMAP is always mapped in TLB1, so
this relieves pressure on TLB0.

MFC after:	3 weeks
2019-08-15 03:42:15 +00:00
Warner Losh
77af66f0d4 Fix powerpc LINT build
tcpratelimit isn't supported as there's now atomic_add_64, so add it to the exclusion list
Add comment for why PPC_PROBE_CHIPSET is on the list
Remove UKBD_DFLT_KEYMAP now that ukbd works on all platforms.
2019-08-12 23:25:21 +00:00
Warner Losh
c1ab04fce5 Floppy driver really only works on x86
Move the floppy driver to the x86 specific notes file.

Reviewed by: jhb, manu, jhibbits, emaste
Differential Revision: https://reviews.freebsd.org/D21208
2019-08-12 22:58:50 +00:00
Warner Losh
99e1c5ab38 Move sc out of the global file
x86 needs sc, as does sparc64. powerpc doesn't use it by default, but some old
powermac notebooks do not work with vt yet for reasons unknonw. Even so, I've
removed it from powerpc LINT. It's not in daily use there, and the intent is to
100% switch to vt now that it works for that platform to limit support burden.

All the other architectures omit some or all of the screen savers from their
lint config. Move them to the x86 NOTES files and remove the exclusions. This
reduces slightly the number of savers sparc64 compiles, but since they are in
GENERIC, the overage is adequate and if someone reaelly wants to sort them out
in sparc64 they can sweat the details and the testing.

Reviewed by: jhb (earlier version), manu (earlier version), jhibbits
Differential Revision: https://reviews.freebsd.org/D21233
2019-08-12 22:58:44 +00:00
Leandro Lupori
26b6a67b98 Fix style and clarify comment
Fix code style in proc.h and clarify comment about empty structs.
2019-08-12 19:44:57 +00:00
Leandro Lupori
4e8872c800 [ppc] avoid empty mdproc struct
Avoid empty structs, that have undefined behavior in C99 and
make compilers complain about it
(empty struct has size 0 in C, size 1 in C++).

Reviewed by:	jhibbits
Differential Revision:	https://reviews.freebsd.org/D21231
2019-08-12 17:18:20 +00:00
Leandro Lupori
b501589d81 [PPC64] Save FPU registers before enabling VSX
Fixed trap handler logic, in order to make it save FPU registers,
if FPU is enabled, before enabling VSX. Without this change, FPU
register contents were being lost when set before VSX was enabled.
2019-08-12 12:51:47 +00:00
Justin Hibbits
3be09f300d powerpc: Unify pmap definitions between AIM and Book-E
This is part 2 of r347078, pulling the page directory out of the Book-E
pmap.  This breaks KBI for anything that uses struct pmap (such as vm_map)
so any modules that access this must be rebuilt.
2019-08-12 03:03:56 +00:00
Justin Hibbits
937e8f20af powerpc/pmap: Minor optimizations to 64-bit booke pmap
Don't recalculate the VM page of the page table pages, just pass them down
to free.  Also, use the pmap's page zero function instead of bzero().
2019-08-08 03:18:35 +00:00
Justin Hibbits
8b1531eca8 Fix build from r350622
It helps if my local kernel build has INVARIANTS.
2019-08-06 03:49:40 +00:00
Justin Hibbits
dc825fed55 powerpc/pmap: Simplify Book-E 64-bit page table management
There is no need for the 64-bit pmap to have a fixed number of page table
buffers.  Since the 64-bit pmap has a DMAP, we can effectively have user
page tables limited only by total RAM size.
2019-08-06 03:16:06 +00:00
Justin Hibbits
2b50838563 powerpc: Get 32-bit AIM building with secure-PLT
The last few changes needed before 32-bit AIM builds with secure-PLT with
base GCC.  Because ofwcall32.S and swtch32.S were branching to the GOT it
could not use secure PLT.
2019-08-05 01:37:18 +00:00
Justin Hibbits
69a277d98e powerpc: Enable the BUS_DMA_NOCACHE flag handling
The flag handling was committed commented out 7 years ago.  It works, and is
needed for LinuxKPI-based DRM drivers.

Also mark a local as potentially unusable, as it's only really used when KTR
is enabled.

Submitted by:	mmacy
2019-08-04 19:25:23 +00:00
Justin Hibbits
84ce4f0375 powerpc/powernv: Fix OPAL cfgread/cfgwrite error handling
Freeze clearing needs to heppen any time OPAL reads return either an error
(except OPAL_HARDWARE), AND any time it returns 0xff for all bytes.

For cfgwrite, any error that's not OPAL_HARDWARE should be cleaned up.
2019-08-03 01:55:51 +00:00
Justin Hibbits
0effb2ccf3 powerpc/powernv: Only clear EEH freeze for some errors
Only clear an EEH freeze if an error occurs.  However, if an OPAL_HARDWARE
error is returned, this indicates a hardware failure which cannot be
unfrozen, and instead needs a hardware reset.  Attempting to unfreeze a
broken PCH will result in console spam for each attempt.  To avoid the spam,
just don't do it.
2019-08-01 03:59:25 +00:00
Justin Hibbits
be01018809 powerpc64/mmu: Use a SLIST for the PVO delete list, instead of a RB_TREE
Summary:
Although it's convenient to reuse the pvo_plist for deletion, RB_TREE
insertion and removal is not free, and can result in a lot of extra work
to rebalance the tree.  Instead, use a SLIST as a LIFO delete queue,
which gives us almost free insertion, deletion, and traversal.

Reviewed by:	luporl
Differential Revision: https://reviews.freebsd.org/D21061
2019-08-01 03:55:58 +00:00
Leandro Lupori
6962841780 powerpc: Improve pvo allocation code
Added allocation retry loop in alloc_pvo_entry(), to wait for
memory to become available if the caller specifies the M_WAITOK flag.

Also, the loop in moa64_enter() was removed, as moea64_pvo_enter()
never returns ENOMEM. It is alloc_pvo_entry() memory allocation that
can fail and must be retried.

Reviewed by:	jhibbits
Differential Revision:	https://reviews.freebsd.org/D21035
2019-07-25 15:27:05 +00:00
Justin Hibbits
7c382eea30 powerpc/pmap64: Make moea64 statistics optional
Summary:
It turns out statistics accounting is very expensive in the pmap driver,
and doesn't seem necessary in the common case.  Make this optional
behind a MOEA64_STATS #define, which one can set if they really need
statistics.

This saves ~7-8% on buildworld time on a POWER9.

Found by bdragon.

Reviewed by:	luporl
Differential Revision: https://reviews.freebsd.org/D20903
2019-07-25 03:47:27 +00:00
Justin Hibbits
b75bd60a04 powerpc: Unbreak 64-bit pmap from 350206
oldpvo is never explicitly NULL'd by moea64_pvo_enter(), so don't check for
NULL to do anything, only check error.

PR:		239372
Reported by:	Francis Little
2019-07-22 22:59:50 +00:00
Justin Hibbits
5db86748b5 powerpc64/mmu: Make moea64_pvo_enter() return if an entry already exists
Summary:
Instead of searching for a PVO entry before adding, take advantage of
the fact that RB_INSERT() returns NULL if it inserts, and the existing entry if
an entry exists, without inserting a new entry.  This saves an extra tree
traversal in the cases where the PVO does not exist.

Reviewed by:	luporl
Differential Revision: https://reviews.freebsd.org/D20944
2019-07-22 03:11:54 +00:00
Justin Hibbits
b982c7ee20 powerpc: Remove an unnecessary #ifdef guard from slb.c
slb.c is only compiled for powerpc64, so no need for the #ifdef in this block.
2019-07-21 03:19:54 +00:00
Justin Hibbits
cafceaebea powerpc/SPE: Enable SPV bit for EFSCFD instruction emulation
EFSCFD (floating point single convert from double) emulation requires saving
the high word of the register, which uses SPE instructions.  Enable the SPE
to avoid an SPV Unavailable exception.

MFC after:	1 week
2019-07-20 18:22:01 +00:00
Justin Hibbits
8d00d89228 powerpc: Fix casueword(9) post-r349951
'=' asm constraint marks a variable as write-only.  Because of this, gcc
throws away the initialization of 'res', causing garbage to be returned if
the CAS was successful.  Use '+' to mark res as read/write, so that the
initialization stays in the generated asm.  Also, fix the reservation
clearing stwcx store index register in casueword32, and only do the dummy
store when needed, skip it if the real store has already succeeded.
2019-07-16 03:55:27 +00:00
John Baldwin
c18ca74916 Don't pass error from syscallenter() to syscallret().
syscallret() doesn't use error anymore.  Fix a few other places to permit
removing the return value from syscallenter() entirely.
- Remove a duplicated assertion from arm's syscall().
- Use td_errno for amd64_syscall_ret_flush_l1d.

Reviewed by:	kib
MFC after:	1 month
Sponsored by:	DARPA
Differential Revision:	https://reviews.freebsd.org/D2090
2019-07-15 21:25:16 +00:00
Justin Hibbits
07b57507c9 powerpc64/pmap: No need for moea64_pvo_remove_from_page_locked() wrapper
The only consumer of moea64_pvo_remove_from_page_locked() already has the
page in hand, so there is no need to search for the page while holding the
lock.  Drop the wrapper, and rename _moea64_pvo_remove_from_page_locked().

Reported by:	alc
2019-07-13 03:39:46 +00:00
Justin Hibbits
a7e6ec601a powerpc64/pmap: Reduce scope of PV_LOCK in remove path
Summary:
Since the 'page pv' lock is one of the most highly contended locks, we
need to try to do as much work outside of the lock as we can.  The
moea64_pvo_remove_from_page() path is a low hanging fruit, where we can
do some heavy work (PHYS_TO_VM_PAGE()) outside of the lock if needed.
In one path, moea64_remove_all(), the PV lock is already held and can't
be swizzled, so we provide two ways to perform the locked operation, one
that can call PHYS_TO_VM_PAGE outside the lock, and one that calls with
the lock already held.

Reviewed By: luporl
Differential Revision: https://reviews.freebsd.org/D20694
2019-07-13 03:02:11 +00:00
Justin Hibbits
21e47be25e Set pcpu curpmap for powerpc64
Summary:
If an illegal instruction is encountered on a process running on a
powerpc64 kernel it would attempt to sync the cache before retrying the
instruction "just in case".  However, since curpmap is not set, when
moea64_sync_icache() attempts to lock the pmap, it's locking on a NULL pointer,
triggering a panic.  Fix this by adding a (assumed unnecessary) fallback to
curthread's pmap in moea64_sync_icache().

Reported by:	alfredo.junior_eldorado.org.br
Reviewed by:	luporl, alfredo.junior_eldorado.org.br
Differential Revision: https://reviews.freebsd.org/D20911
2019-07-13 00:19:57 +00:00
Konstantin Belousov
30b3018d48 Provide protection against starvation of the ll/sc loops when accessing userpace.
Casueword(9) on ll/sc architectures must be prepared for userspace
constantly modifying the same cache line as containing the CAS word,
and not loop infinitely.  Otherwise, rogue userspace livelocks the
kernel.

To fix the issue, change casueword(9) interface to return new value 1
indicating that either comparision or store failed, instead of relying
on the oldval == *oldvalp comparison.  The primitive no longer retries
the operation if it failed spuriously.  Modify callers of
casueword(9), all in kern_umtx.c, to handle retries, and react to
stops and requests to terminate between retries.

On x86, despite cmpxchg should not return spurious failures, we can
take advantage of the new interface and just return PSL.ZF.

Reviewed by:	andrew (arm64, previous version), markj
Tested by:	pho
Reported by:	https://xenbits.xen.org/xsa/advisory-295.txt
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Differential revision:	https://reviews.freebsd.org/D20772
2019-07-12 18:43:24 +00:00
Justin Hibbits
9ac516a6f1 powerpc: Only worry about the lower 32 bits of SP in a 32-bit process
Summary:
Running a 32-bit process on a 64-bit POWER CPU may still use all 64-bits
in calculations, while ignoring the upper 32 bits for addressing
storage.  It so happens that some processes end up with r1 (SP) having
bit 31 set in some cases (33-bit address).  Writing out to this 33-bit
address obviosly fails.  Since the CPU ignores the upper bits, we should
as well.

sendsig() and cpu_fetch_syscall_args() appear to be the only functions
that actually rely on userspace register values for copy in/out, and
cpu_fetch_syscall_args() doesn't seem to be bitten in practice yet.

Reviewed By: luporl
Differential Revision: https://reviews.freebsd.org/D20896
2019-07-11 03:29:25 +00:00
Leandro Lupori
8b55f9f853 [PPC64] pseries: fix realmaxaddr calculation
On POWER9/pseries, QEMU passes several regions of memory,
instead of a single region containing all memory, as the
code was expecting.

Reviewed by:	jhibbits
Differential Revision:	https://reviews.freebsd.org/D20857
2019-07-10 13:36:17 +00:00
Justin Hibbits
b51bfc30ac powerpc: Clamp 32-bit binaries to 32-bit MAXUSER
sv_maxuser specifies the maximum addressable space for user space.  Presently
this is all 64-bits worth, which is impossible for a 32-bit process.

This bug has existed since the initial import of powerpc64 in 2010.

MFC after:	2 weeks
2019-07-10 04:09:15 +00:00
Mark Johnston
eeacb3b02f Merge the vm_page hold and wire mechanisms.
The hold_count and wire_count fields of struct vm_page are separate
reference counters with similar semantics.  The remaining essential
differences are that holds are not counted as a reference with respect
to LRU, and holds have an implicit free-on-last unhold semantic whereas
vm_page_unwire() callers must explicitly determine whether to free the
page once the last reference to the page is released.

This change removes the KPIs which directly manipulate hold_count.
Functions such as vm_fault_quick_hold_pages() now return wired pages
instead.  Since r328977 the overhead of maintaining LRU for wired pages
is lower, and in many cases vm_fault_quick_hold_pages() callers would
swap holds for wirings on the returned pages anyway, so with this change
we remove a number of page lock acquisitions.

No functional change is intended.  __FreeBSD_version is bumped.

Reviewed by:	alc, kib
Discussed with:	jeff
Discussed with:	jhb, np (cxgbe)
Tested by:	pho (previous version)
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D19247
2019-07-08 19:46:20 +00:00