06 Aug, 2020
1 commit
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MIPS already uses and S390 will need the vdso data pointer in
__arch_get_hw_counter().This works nicely as long as the architecture does not support time
namespaces in the VDSO. With time namespaces enabled the regular
accessor to the vdso data pointer __arch_get_vdso_data() will return the
namespace specific VDSO data page for tasks which are part of a
non-root time namespace. This would cause the architectures which need
the vdso data pointer in __arch_get_hw_counter() to access the wrong
vdso data page.Add a vdso_data pointer argument to __arch_get_hw_counter() and hand it in
from the call sites in the core code. For architectures which do not need
the data pointer in their counter accessor function the compiler will just
optimize it out.Fix up all existing architecture implementations and make MIPS utilize the
pointer instead of invoking the accessor function.No functional change and no change in the resulting object code (except
MIPS).Signed-off-by: Thomas Gleixner
Link: https://lkml.kernel.org/r/draft-87wo2ekuzn.fsf@nanos.tec.linutronix.de
12 Jun, 2020
1 commit
-
Pull more x86 updates from Thomas Gleixner:
"A set of fixes and updates for x86:- Unbreak paravirt VDSO clocks.
While the VDSO code was moved into lib for sharing a subtle check
for the validity of paravirt clocks got replaced. While the
replacement works perfectly fine for bare metal as the update of
the VDSO clock mode is synchronous, it fails for paravirt clocks
because the hypervisor can invalidate them asynchronously.Bring it back as an optional function so it does not inflict this
on architectures which are free of PV damage.- Fix the jiffies to jiffies64 mapping on 64bit so it does not
trigger an ODR violation on newer compilers- Three fixes for the SSBD and *IB* speculation mitigation maze to
ensure consistency, not disabling of some *IB* variants wrongly and
to prevent a rogue cross process shutdown of SSBD. All marked for
stable.- Add yet more CPU models to the splitlock detection capable list
!@#%$!- Bring the pr_info() back which tells that TSC deadline timer is
enabled.- Reboot quirk for MacBook6,1"
* tag 'x86-urgent-2020-06-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/vdso: Unbreak paravirt VDSO clocks
lib/vdso: Provide sanity check for cycles (again)
clocksource: Remove obsolete ifdef
x86_64: Fix jiffies ODR violation
x86/speculation: PR_SPEC_FORCE_DISABLE enforcement for indirect branches.
x86/speculation: Prevent rogue cross-process SSBD shutdown
x86/speculation: Avoid force-disabling IBPB based on STIBP and enhanced IBRS.
x86/cpu: Add Sapphire Rapids CPU model number
x86/split_lock: Add Icelake microserver and Tigerlake CPU models
x86/apic: Make TSC deadline timer detection message visible
x86/reboot/quirks: Add MacBook6,1 reboot quirk
09 Jun, 2020
1 commit
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The original x86 VDSO implementation checked for the validity of the clock
source read by testing whether the returned signed cycles value is less
than zero. This check was also used by the vdso read function to signal
that the current selected clocksource is not VDSO capable.During the rework of the VDSO code the check was removed and replaced with
a check for the clocksource mode being != NONE.This turned out to be a mistake because the check is necessary for paravirt
and hyperv clock sources. The reason is that these clock sources have their
own internal sequence counter to validate the clocksource at the point of
reading it. This is necessary because the hypervisor can invalidate the
clocksource asynchronously so a check during the VDSO data update is not
sufficient. Having a separate indicator for the validity is slower than
just validating the cycles value. The check for it being negative turned
out to be the fastest implementation and safe as it would require an uptime
of ~73 years with a 4GHz counter frequency to result in a false positive.Add an optional function to validate the cycles with a default
implementation which allows the compiler to optimize it out for
architectures which do not require it.Fixes: 5d51bee725cc ("clocksource: Add common vdso clock mode storage")
Reported-by: Miklos Szeredi
Signed-off-by: Thomas Gleixner
Tested-by: Miklos Szeredi
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20200606221531.963970768@linutronix.de
04 Jun, 2020
1 commit
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When adding gettime64() to a 32 bit architecture (namely powerpc/32)
it has been noticed that GCC doesn't inline anymore
__cvdso_clock_gettime_common() because it is called twice
(Once by __cvdso_clock_gettime() and once by
__cvdso_clock_gettime32).This has the effect of seriously degrading the performance:
Before the implementation of gettime64(), gettime() runs in:
clock-gettime-monotonic-raw: vdso: 1003 nsec/call
clock-gettime-monotonic-coarse: vdso: 592 nsec/call
clock-gettime-monotonic: vdso: 942 nsec/callWhen adding a gettime64() entry point, the standard gettime()
performance is degraded by 30% to 50%:clock-gettime-monotonic-raw: vdso: 1300 nsec/call
clock-gettime-monotonic-coarse: vdso: 900 nsec/call
clock-gettime-monotonic: vdso: 1232 nsec/callAdding __always_inline() to __cvdso_clock_gettime_common() regains the
original performance.In terms of code size, the inlining increases the code size by only 176
bytes. This is in the noise for a kernel image.Signed-off-by: Christophe Leroy
Signed-off-by: Thomas Gleixner
Link: https://lkml.kernel.org/r/1ab6a62c356c3bec35d1623563ef9c636205bcda.1588079622.git.christophe.leroy@c-s.fr
21 Mar, 2020
1 commit
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The vDSO library should only include the necessary headers required for
a userspace library (UAPI and a minimal set of kernel headers). To make
this possible it is necessary to isolate from the kernel headers the
common parts that are strictly necessary to build the library.Refactor the unified vdso code to use the common headers.
Signed-off-by: Vincenzo Frascino
Signed-off-by: Thomas Gleixner
Link: https://lkml.kernel.org/r/20200320145351.32292-26-vincenzo.frascino@arm.com
18 Feb, 2020
5 commits
-
On powerpc, __arch_get_vdso_data() clobbers the link register, requiring
the caller to save it.As the parent function already has to set a stack frame and saves the link
register before calling the C vdso function, retrieving the vdso data
pointer there is less overhead.Split out the functional code from the __cvdso.*() interfaces into new
static functions which can either be called from the existing interfaces
with the vdso data pointer supplied via __arch_get_vdso_data() or directly
from ASM code.Signed-off-by: Christophe Leroy
Signed-off-by: Thomas Gleixner
Tested-by: Vincenzo Frascino
Reviewed-by: Vincenzo Frascino
Link: https://lore.kernel.org/r/abf97996602ef07223fec30c005df78e5ed41b2e.1580399657.git.christophe.leroy@c-s.fr
Link: https://lkml.kernel.org/r/20200207124403.965789141@linutronix.de -
On powerpc/32, GCC (8.1) generates pretty bad code for the ns >>= vd->shift
operation taking into account that the shift is always = 32 and the upper part to be like not
zero.unsigned long long shift(unsigned long long x, unsigned char s)
{
return x >> s;
}results in:
00000018 :
18: 35 25 ff e0 addic. r9,r5,-32
1c: 41 80 00 10 blt 2c
20: 7c 64 4c 30 srw r4,r3,r9
24: 38 60 00 00 li r3,0
28: 4e 80 00 20 blr
2c: 54 69 08 3c rlwinm r9,r3,1,0,30
30: 21 45 00 1f subfic r10,r5,31
34: 7c 84 2c 30 srw r4,r4,r5
38: 7d 29 50 30 slw r9,r9,r10
3c: 7c 63 2c 30 srw r3,r3,r5
40: 7d 24 23 78 or r4,r9,r4
44: 4e 80 00 20 blrEven when forcing the shift to be smaller than 32 with an &= 31, it still
considers the shift as likely >= 32.Move the default shift implementation into an inline which can be redefined
in architecture code via a macro.[ tglx: Made the shift argument u32 and removed the __arch prefix ]
Signed-off-by: Christophe Leroy
Signed-off-by: Thomas Gleixner
Tested-by: Vincenzo Frascino
Reviewed-by: Vincenzo Frascino
Link: https://lore.kernel.org/r/b3d449de856982ed060a71e6ace8eeca4654e685.1580399657.git.christophe.leroy@c-s.fr
Link: https://lkml.kernel.org/r/20200207124403.857649978@linutronix.de -
Some architectures have a fixed clocksource which is known at compile time
and cannot be replaced or disabled at runtime, e.g. timebase on
PowerPC. For such cases the clock mode check in the VDSO code is pointless.Move the check for a VDSO capable clocksource into an inline function and
allow architectures to redefine it via a macro.[ tglx: Removed the #ifdef mess ]
Signed-off-by: Christophe Leroy
Signed-off-by: Thomas Gleixner
Tested-by: Vincenzo Frascino
Reviewed-by: Vincenzo Frascino
Link: https://lkml.kernel.org/r/20200207124403.748756829@linutronix.de -
Move the time namespace indicator clock mode to the other ones for
consistency sake.Signed-off-by: Thomas Gleixner
Reviewed-by: Vincenzo Frascino
Link: https://lkml.kernel.org/r/20200207124403.656097274@linutronix.de -
Now that all architectures are converted to use the generic storage the
helpers and conditionals can be removed.Signed-off-by: Thomas Gleixner
Tested-by: Vincenzo Frascino
Reviewed-by: Vincenzo Frascino
Link: https://lkml.kernel.org/r/20200207124403.470699892@linutronix.de
17 Feb, 2020
2 commits
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All architectures which use the generic VDSO code have their own storage
for the VDSO clock mode. That's pointless and just requires duplicate code.Provide generic storage for it. The new Kconfig symbol is intermediate and
will be removed once all architectures are converted over.Signed-off-by: Thomas Gleixner
Tested-by: Vincenzo Frascino
Reviewed-by: Vincenzo Frascino
Link: https://lkml.kernel.org/r/20200207124403.028046322@linutronix.de -
If the architecture knows at compile time that there is no VDSO capable
clocksource supported it makes sense to optimize the guts of the high
resolution parts of the VDSO out at build time. Add a helper function to
check whether the VDSO should be high resolution capable and provide a stub
which can be overridden by an architecture.Signed-off-by: Thomas Gleixner
Tested-by: Vincenzo Frascino
Reviewed-by: Vincenzo Frascino
Link: https://lkml.kernel.org/r/20200207124402.530143168@linutronix.de
17 Jan, 2020
1 commit
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Only perform READ_ONCE(vd[CS_HRES_COARSE].hrtimer_res) for
HRES and RAW clocks.Signed-off-by: Christophe Leroy
Signed-off-by: Thomas Gleixner
Link: https://lore.kernel.org/r/7ac2f0d21652f95e2bbdfa6bd514ae6c7caf53ab.1579196675.git.christophe.leroy@c-s.fr
14 Jan, 2020
7 commits
-
To support time namespaces in the vdso with a minimal impact on regular non
time namespace affected tasks, the namespace handling needs to be hidden in
a slow path.The most obvious place is vdso_seq_begin(). If a task belongs to a time
namespace then the VVAR page which contains the system wide vdso data is
replaced with a namespace specific page which has the same layout as the
VVAR page. That page has vdso_data->seq set to 1 to enforce the slow path
and vdso_data->clock_mode set to VCLOCK_TIMENS to enforce the time
namespace handling path.The extra check in the case that vdso_data->seq is odd, e.g. a concurrent
update of the vdso data is in progress, is not really affecting regular
tasks which are not part of a time namespace as the task is spin waiting
for the update to finish and vdso_data->seq to become even again.If a time namespace task hits that code path, it invokes the corresponding
time getter function which retrieves the real VVAR page, reads host time
and then adds the offset for the requested clock which is stored in the
special VVAR page.If VDSO time namespace support is disabled the whole magic is compiled out.
Initial testing shows that the disabled case is almost identical to the
host case which does not take the slow timens path. With the special timens
page installed the performance hit is constant time and in the range of
5-7%.For the vdso functions which are not using the sequence count an
unconditional check for vdso_data->clock_mode is added which switches to
the real vdso when the clock_mode is VCLOCK_TIMENS.[avagin: Make do_hres_timens() work with raw clocks too: choose vdso_data
pointer by CS_RAW offset.]Suggested-by: Andy Lutomirski
Signed-off-by: Thomas Gleixner
Signed-off-by: Andrei Vagin
Signed-off-by: Dmitry Safonov
Signed-off-by: Thomas Gleixner
Link: https://lore.kernel.org/r/20191112012724.250792-21-dima@arista.com -
Performance numbers for Intel(R) Core(TM) i5-6300U CPU @ 2.40GHz
(more clock_gettime() cycles - the better):clock | before | after | diff
----------------------------------------------------------
monotonic | 153222105 | 166775025 | 8.8%
monotonic-coarse | 671557054 | 691513017 | 3.0%
monotonic-raw | 147116067 | 161057395 | 9.5%
boottime | 153446224 | 166962668 | 9.1%The improvement for arm64 for monotonic and boottime is around 3.5%.
clock | before | after | diff
==================================================
monotonic 17326692 17951770 3.6%
monotonic-coarse 43624027 44215292 1.3%
monotonic-raw 17541809 17554932 0.1%
boottime 17334982 17954361 3.5%[ tglx: Avoid the goto ]
Signed-off-by: Andrei Vagin
Signed-off-by: Dmitry Safonov
Signed-off-by: Thomas Gleixner
Link: https://lore.kernel.org/r/20191112012724.250792-3-dima@arista.com -
VDSO_HRES and VDSO_RAW clocks are handled the same way.
Avoid the code duplication.
Signed-off-by: Christophe Leroy
Signed-off-by: Thomas Gleixner
Reviewed-by: Andy Lutomirski
Link: https://lore.kernel.org/r/fdf1a968a8f7edd61456f1689ac44082ebb19c15.1577111367.git.christophe.leroy@c-s.fr -
do_coarse() is similar to do_hres() except that it never fails.
Change its type to int instead of void and let it always return success (0)
to simplify the call site.Signed-off-by: Christophe Leroy
Signed-off-by: Thomas Gleixner
Link: https://lore.kernel.org/r/21e8afa38c02ca8672c2690307383507fe63b454.1577111367.git.christophe.leroy@c-s.fr -
Since all the architectures that support the generic vDSO library have
been converted to support the 32 bit fallbacks it is not required
anymore to check the return value of __cvdso_clock_get*time32_common()
before updating the old_timespec fields.Remove the related checks from the generic vdso library.
References: c60a32ea4f45 ("lib/vdso/32: Provide legacy syscall fallbacks")
Signed-off-by: Vincenzo Frascino
Signed-off-by: Thomas Gleixner
Link: https://lore.kernel.org/r/20190830135902.20861-6-vincenzo.frascino@arm.com -
VDSO_HAS_32BIT_FALLBACK was introduced to address a regression which
caused seccomp to deny access to the applications to clock_gettime64()
and clock_getres64() because they are not enabled in the existing
filters.The purpose of VDSO_HAS_32BIT_FALLBACK was to simplify the conditional
implementation of __cvdso_clock_get*time32() variants.Now that all the architectures that support the generic vDSO library
have been converted to support the 32 bit fallbacks the conditional
can be removed.Signed-off-by: Vincenzo Frascino
Signed-off-by: Thomas Gleixner
Link: https://lore.kernel.org/r/20190830135902.20861-5-vincenzo.frascino@arm.comReferences: c60a32ea4f45 ("lib/vdso/32: Provide legacy syscall fallbacks")
-
clock_gettime32 and clock_getres_time32 should be compiled only with a
32 bit vdso library.Exclude these symbols when BUILD_VDSO32 is not defined.
Signed-off-by: Vincenzo Frascino
Signed-off-by: Thomas Gleixner
Reviewed-by: Andy Lutomirski
Link: https://lore.kernel.org/r/20190830135902.20861-3-vincenzo.frascino@arm.com
11 Jan, 2020
1 commit
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Fix the following sparse warning in the generic vDSO library:
linux/lib/vdso/gettimeofday.c:224:5: warning: symbol
'__cvdso_clock_getres' was not declared. Should it be static?Make it static and also mark it __maybe_unsed.
Fixes: 502a590a170b ("lib/vdso: Move fallback invocation to the callers")
Reported-by: Marc Gonzalez
Signed-off-by: Vincenzo Frascino
Signed-off-by: Thomas Gleixner
Link: https://lore.kernel.org/r/20191128111719.8282-1-vincenzo.frascino@arm.com
15 Nov, 2019
1 commit
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Only x86 uses the 'time' syscall in vdso, so change that to
__kernel_old_time_t as a preparation for removing 'time_t' and
'__kernel_time_t' later.Reviewed-by: Thomas Gleixner
Signed-off-by: Arnd Bergmann
23 Oct, 2019
1 commit
-
A recent commit removed the NULL pointer check from the clock_getres()
implementation causing a test case to fault.POSIX requires an explicit NULL pointer check for clock_getres() aside of
the validity check of the clock_id argument for obscure reasons.Add it back for both 32bit and 64bit.
Note, this is only a partial revert of the offending commit which does not
bring back the broken fallback invocation in the the 32bit compat
implementations of clock_getres() and clock_gettime().Fixes: a9446a906f52 ("lib/vdso/32: Remove inconsistent NULL pointer checks")
Reported-by: Andreas Schwab
Signed-off-by: Thomas Gleixner
Tested-by: Christophe Leroy
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1910211202260.1904@nanos.tec.linutronix.de
07 Oct, 2019
1 commit
-
arm64 was the last architecture using CROSS_COMPILE_COMPAT_VDSO config
option. With this patch series the dependency in the architecture has
been removed.Remove CROSS_COMPILE_COMPAT_VDSO from the Unified vDSO library code.
Cc: Thomas Gleixner
Cc: Andy Lutomirski
Signed-off-by: Vincenzo Frascino
Signed-off-by: Will Deacon
31 Jul, 2019
3 commits
-
To address the regression which causes seccomp to deny applications the
access to clock_gettime64() and clock_getres64() syscalls because they
are not enabled in the existing filters.That trips over the fact that 32bit VDSOs use the new clock_gettime64() and
clock_getres64() syscalls in the fallback path.Add a conditional to invoke the 32bit legacy fallback syscalls instead of
the new 64bit variants. The conditional can go away once all architectures
are converted.Fixes: 00b26474c2f1 ("lib/vdso: Provide generic VDSO implementation")
Signed-off-by: Thomas Gleixner
Tested-by: Sean Christopherson
Reviewed-by: Sean Christopherson
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1907301134470.1738@nanos.tec.linutronix.de -
To allow syscall fallbacks using the legacy 32bit syscall for 32bit VDSO
builds, move the fallback invocation out into the callers.Split the common code out of __cvdso_clock_gettime/getres() and invoke the
syscall fallback in the 64bit and 32bit variants.Preparatory work for using legacy syscalls in 32bit VDSO. No functional
change.Fixes: 00b26474c2f1 ("lib/vdso: Provide generic VDSO implementation")
Signed-off-by: Thomas Gleixner
Tested-by: Vincenzo Frascino
Reviewed-by: Andy Lutomirski
Reviewed-by: Vincenzo Frascino
Link: https://lkml.kernel.org/r/20190728131648.695579736@linutronix.de -
The 32bit variants of vdso_clock_gettime()/getres() have a NULL pointer
check for the timespec pointer. That's inconsistent vs. 64bit.But the vdso implementation will never be consistent versus the syscall
because the only case which it can handle is NULL. Any other invalid
pointer will cause a segfault. So special casing NULL is not really useful.Remove it along with the superflouos syscall fallback invocation as that
will return -EFAULT anyway. That also gets rid of the dubious typecast
which only works because the pointer is NULL.Fixes: 00b26474c2f1 ("lib/vdso: Provide generic VDSO implementation")
Signed-off-by: Thomas Gleixner
Tested-by: Vincenzo Frascino
Reviewed-by: Vincenzo Frascino
Reviewed-by: Andy Lutomirski
Link: https://lkml.kernel.org/r/20190728131648.587523358@linutronix.de
26 Jun, 2019
1 commit
-
The x86 vdso implementation on which the generic vdso library is based on
has subtle (unfortunately undocumented) twists:1) The code assumes that the clocksource mask is U64_MAX which means that
no bits are masked. Which is true for any valid x86 VDSO clocksource.
Stupidly it still did the mask operation for no reason and at the wrong
place right after reading the clocksource.2) It contains a sanity check to catch the case where slightly
unsynchronized TSC values can be observed which would cause the delta
calculation to make a huge jump. It therefore checks whether the
current TSC value is larger than the value on which the current
conversion is based on. If it's not larger the base value is used to
prevent time jumps.#1 Is not only stupid for the X86 case because it does the masking for no
reason it is also completely wrong for clocksources with a smaller mask
which can legitimately wrap around during a conversion period. The core
timekeeping code does it correct by applying the mask after the delta
calculation:(now - base) & mask
#2 is equally broken for clocksources which have smaller masks and can wrap
around during a conversion period because there the now > base check is
just wrong and causes stale time stamps and time going backwards issues.Unbreak it by:
1) Removing the mask operation from the clocksource read which makes the
fallback detection work for all clocksources2) Replacing the conditional delta calculation with a overrideable inline
function.#2 could reuse clocksource_delta() from the timekeeping code but that
results in a significant performance hit for the x86 VSDO. The timekeeping
core code must have the non optimized version as it has to operate
correctly with clocksources which have smaller masks as well to handle the
case where TSC is discarded as timekeeper clocksource and replaced by HPET
or pmtimer. For the VDSO there is no replacement clocksource. If TSC is
unusable the syscall is enforced which does the right thing.To accommodate to the needs of various architectures provide an
override-able inline function which defaults to the regular delta
calculation with masking:(now - base) & mask
Override it for x86 with the non-masking and checking version.
This unbreaks the ARM64 syscall fallback operation, allows to use
clocksources with arbitrary width and preserves the performance
optimization for x86.Signed-off-by: Thomas Gleixner
Reviewed-by: Vincenzo Frascino
Cc: linux-arch@vger.kernel.org
Cc: LAK
Cc: linux-mips@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org
Cc: catalin.marinas@arm.com
Cc: Will Deacon
Cc: Arnd Bergmann
Cc: linux@armlinux.org.uk
Cc: Ralf Baechle
Cc: paul.burton@mips.com
Cc: Daniel Lezcano
Cc: salyzyn@android.com
Cc: pcc@google.com
Cc: shuah@kernel.org
Cc: 0x7f454c46@gmail.com
Cc: linux@rasmusvillemoes.dk
Cc: huw@codeweavers.com
Cc: sthotton@marvell.com
Cc: andre.przywara@arm.com
Cc: Andy Lutomirski
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1906261159230.32342@nanos.tec.linutronix.de
23 Jun, 2019
2 commits
-
Some 64 bit architectures have support for 32 bit applications that
require a separate version of the vDSOs.Add support to the generic code for compat fallback functions.
Signed-off-by: Vincenzo Frascino
Signed-off-by: Thomas Gleixner
Tested-by: Shijith Thotton
Tested-by: Andre Przywara
Cc: linux-arch@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-mips@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org
Cc: Catalin Marinas
Cc: Will Deacon
Cc: Arnd Bergmann
Cc: Russell King
Cc: Ralf Baechle
Cc: Paul Burton
Cc: Daniel Lezcano
Cc: Mark Salyzyn
Cc: Peter Collingbourne
Cc: Shuah Khan
Cc: Dmitry Safonov
Cc: Rasmus Villemoes
Cc: Huw Davies
Link: https://lkml.kernel.org/r/20190621095252.32307-10-vincenzo.frascino@arm.com -
In the last few years the kernel gained quite some architecture specific
vdso implementations which contain very similar code.Introduce a generic VDSO implementation of gettimeofday() which will be
shareable between architectures once they are converted over.The implementation is based on the current x86 VDSO code.
[ tglx: Massaged changelog and made the kernel doc tabular ]
Signed-off-by: Vincenzo Frascino
Signed-off-by: Thomas Gleixner
Tested-by: Shijith Thotton
Tested-by: Andre Przywara
Cc: linux-arch@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-mips@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org
Cc: Catalin Marinas
Cc: Will Deacon
Cc: Arnd Bergmann
Cc: Russell King
Cc: Ralf Baechle
Cc: Paul Burton
Cc: Daniel Lezcano
Cc: Mark Salyzyn
Cc: Peter Collingbourne
Cc: Shuah Khan
Cc: Dmitry Safonov
Cc: Rasmus Villemoes
Cc: Huw Davies
Link: https://lkml.kernel.org/r/20190621095252.32307-3-vincenzo.frascino@arm.com