The problem:
On -rt, an emulated LAPIC timer instances has the following path:
1) hard interrupt
2) ksoftirqd is scheduled
3) ksoftirqd wakes up vcpu thread
4) vcpu thread is scheduled
This extra context switch introduces unnecessary latency in the
LAPIC path for a KVM guest.
The solution:
Allow waking up vcpu thread from hardirq context,
thus avoiding the need for ksoftirqd to be scheduled.
Normal waitqueues make use of spinlocks, which on -RT
are sleepable locks. Therefore, waking up a waitqueue
waiter involves locking a sleeping lock, which
is not allowed from hard interrupt context.
cyclictest command line:
This patch reduces the average latency in my tests from 14us to 11us.
Daniel writes:
Paolo asked for numbers from kvm-unit-tests/tscdeadline_latency
benchmark on mainline. The test was run 1000 times on
tip/sched/core 4.4.0-rc8-01134-g0905f04:
./x86-run x86/tscdeadline_latency.flat -cpu host
with idle=poll.
The test seems not to deliver really stable numbers though most of
them are smaller. Paolo write:
"Anything above ~10000 cycles means that the host went to C1 or
lower---the number means more or less nothing in that case.
The mean shows an improvement indeed."
Before:
min max mean std
count 1000.000000 1000.000000 1000.000000 1000.000000
mean 5162.596000 2019270.084000 5824.491541 20681.645558
std 75.431231 622607.723969 89.575700 6492.272062
min 4466.000000 23928.000000 5537.926500 585.864966
25% 5163.000000 1613252.750000 5790.132275 16683.745433
50% 5175.000000 2281919.000000 5834.654000 23151.990026
75% 5190.000000 2382865.750000 5861.412950 24148.206168
max 5228.000000 4175158.000000 6254.827300 46481.048691
After
min max mean std
count 1000.000000 1000.00000 1000.000000 1000.000000
mean 5143.511000 2076886.10300 5813.312474 21207.357565
std 77.668322 610413.09583 86.541500 6331.915127
min 4427.000000 25103.00000 5529.756600 559.187707
25% 5148.000000 1691272.75000 5784.889825 17473.518244
50% 5160.000000 2308328.50000 5832.025000 23464.837068
75% 5172.000000 2393037.75000 5853.177675 24223.969976
max 5222.000000 3922458.00000 6186.720500 42520.379830
[Patch was originaly based on the swait implementation found in the -rt
tree. Daniel ported it to mainline's version and gathered the
benchmark numbers for tscdeadline_latency test.]
Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-rt-users@vger.kernel.org
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1455871601-27484-4-git-send-email-wagi@monom.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Using oldstyle vcpu_reg() accessor is proven to be inappropriate and
unsafe on ARM64. This patch converts the rest of use cases to new
accessors and completely removes vcpu_reg() on ARM64.
Signed-off-by: Pavel Fedin <p.fedin@samsung.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
The kvm_vcpu_arch pause field is renamed into power_off to prepare
for the introduction of a new pause field. Also vcpu_pause is renamed
into vcpu_sleep since we will sleep until both power_off and pause are
false.
Signed-off-by: Eric Auger <eric.auger@linaro.org>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
If a guest requests the affinity info for a non-existing vCPU we need to
properly return an error, instead of erroneously reporting an off state.
Signed-off-by: Alexander Spyridakis <a.spyridakis@virtualopensystems.com>
Signed-off-by: Alvise Rigo <a.rigo@virtualopensystems.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
- CPU ops and PSCI (Power State Coordination Interface) refactoring
following the merging of the arm64 ACPI support, together with
handling of Trusted (secure) OS instances
- Using fixmap for permanent FDT mapping, removing the initial dtb
placement requirements (within 512MB from the start of the kernel
image). This required moving the FDT self reservation out of the
memreserve processing
- Idmap (1:1 mapping used for MMU on/off) handling clean-up
- Removing flush_cache_all() - not safe on ARM unless the MMU is off.
Last stages of CPU power down/up are handled by firmware already
- "Alternatives" (run-time code patching) refactoring and support for
immediate branch patching, GICv3 CPU interface access
- User faults handling clean-up
And some fixes:
- Fix for VDSO building with broken ELF toolchains
- Fixing another case of init_mm.pgd usage for user mappings (during
ASID roll-over broadcasting)
- Fix for FPSIMD reloading after CPU hotplug
- Fix for missing syscall trace exit
- Workaround for .inst asm bug
- Compat fix for switching the user tls tpidr_el0 register
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Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux
Pull arm64 updates from Catalin Marinas:
"Mostly refactoring/clean-up:
- CPU ops and PSCI (Power State Coordination Interface) refactoring
following the merging of the arm64 ACPI support, together with
handling of Trusted (secure) OS instances
- Using fixmap for permanent FDT mapping, removing the initial dtb
placement requirements (within 512MB from the start of the kernel
image). This required moving the FDT self reservation out of the
memreserve processing
- Idmap (1:1 mapping used for MMU on/off) handling clean-up
- Removing flush_cache_all() - not safe on ARM unless the MMU is off.
Last stages of CPU power down/up are handled by firmware already
- "Alternatives" (run-time code patching) refactoring and support for
immediate branch patching, GICv3 CPU interface access
- User faults handling clean-up
And some fixes:
- Fix for VDSO building with broken ELF toolchains
- Fix another case of init_mm.pgd usage for user mappings (during
ASID roll-over broadcasting)
- Fix for FPSIMD reloading after CPU hotplug
- Fix for missing syscall trace exit
- Workaround for .inst asm bug
- Compat fix for switching the user tls tpidr_el0 register"
* tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (42 commits)
arm64: use private ratelimit state along with show_unhandled_signals
arm64: show unhandled SP/PC alignment faults
arm64: vdso: work-around broken ELF toolchains in Makefile
arm64: kernel: rename __cpu_suspend to keep it aligned with arm
arm64: compat: print compat_sp instead of sp
arm64: mm: Fix freeing of the wrong memmap entries with !SPARSEMEM_VMEMMAP
arm64: entry: fix context tracking for el0_sp_pc
arm64: defconfig: enable memtest
arm64: mm: remove reference to tlb.S from comment block
arm64: Do not attempt to use init_mm in reset_context()
arm64: KVM: Switch vgic save/restore to alternative_insn
arm64: alternative: Introduce feature for GICv3 CPU interface
arm64: psci: fix !CONFIG_HOTPLUG_CPU build warning
arm64: fix bug for reloading FPSIMD state after CPU hotplug.
arm64: kernel thread don't need to save fpsimd context.
arm64: fix missing syscall trace exit
arm64: alternative: Work around .inst assembler bugs
arm64: alternative: Merge alternative-asm.h into alternative.h
arm64: alternative: Allow immediate branch as alternative instruction
arm64: Rework alternate sequence for ARM erratum 845719
...
According to the PSCI specification and the SMC/HVC calling
convention, PSCI function_ids that are not implemented must
return NOT_SUPPORTED as return value.
Current KVM implementation takes an unhandled PSCI function_id
as an error and injects an undefined instruction into the guest
if PSCI implementation is called with a function_id that is not
handled by the resident PSCI version (ie it is not implemented),
which is not the behaviour expected by a guest when calling a
PSCI function_id that is not implemented.
This patch fixes this issue by returning NOT_SUPPORTED whenever
the kvm PSCI call is executed for a function_id that is not
implemented by the PSCI kvm layer.
Cc: <stable@vger.kernel.org> # 3.18+
Cc: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
We make use of the PSCI function IDs, but don't explicitly include the
header which defines them. Relying on transitive header includes is
fragile and will be broken as headers are refactored.
This patch includes the relevant header file directly so as to avoid
future breakage.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Reviewed-by: Hanjun Guo <hanjun.guo@linaro.org>
Tested-by: Hanjun Guo <hanjun.guo@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
The virtual MPIDR registers (containing topology information) for the
guest are currently mapped linearily to the vcpu_id. Improve this
mapping for arm64 by using three levels to not artificially limit the
number of vCPUs.
To help this, change and rename the kvm_vcpu_get_mpidr() function to
mask off the non-affinity bits in the MPIDR register.
Also add an accessor to later allow easier access to a vCPU with a
given MPIDR. Use this new accessor in the PSCI emulation.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
When a vcpu calls SYSTEM_OFF or SYSTEM_RESET with PSCI v0.2, the vcpus
should really be turned off for the VM adhering to the suggestions in
the PSCI spec, and it's the sane thing to do.
Also, clarify the behavior and expectations for exits to user space with
the KVM_EXIT_SYSTEM_EVENT case.
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
This patch adds emulation of PSCI v0.2 CPU_SUSPEND function call for
KVM ARM/ARM64. This is a CPU-level function call which can suspend
current CPU or current CPU cluster. We don't have VCPU clusters in
KVM so we only suspend the current VCPU.
The CPU_SUSPEND emulation is not tested much because currently there
is no CPUIDLE driver in Linux kernel that uses PSCI CPU_SUSPEND. The
PSCI CPU_SUSPEND implementation in ARM64 kernel was tested using a
Simple CPUIDLE driver which is not published due to unstable DT-bindings
for PSCI.
(For more info, http://lwn.net/Articles/574950/)
For simplicity, we implement CPU_SUSPEND emulation similar to WFI
(Wait-for-interrupt) emulation and we also treat power-down request
to be same as stand-by request. This is consistent with section
5.4.1 and section 5.4.2 of PSCI v0.2 specification.
Signed-off-by: Anup Patel <anup.patel@linaro.org>
Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
As-per PSCI v0.2, the source CPU provides physical address of
"entry point" and "context id" for starting a target CPU. Also,
if target CPU is already running then we should return ALREADY_ON.
Current emulation of CPU_ON function does not consider physical
address of "context id" and returns INVALID_PARAMETERS if target
CPU is already running.
This patch updates kvm_psci_vcpu_on() such that it works for both
PSCI v0.1 and PSCI v0.2.
Signed-off-by: Anup Patel <anup.patel@linaro.org>
Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
This patch adds emulation of PSCI v0.2 MIGRATE, MIGRATE_INFO_TYPE, and
MIGRATE_INFO_UP_CPU function calls for KVM ARM/ARM64.
KVM ARM/ARM64 being a hypervisor (and not a Trusted OS), we cannot provide
this functions hence we emulate these functions in following way:
1. MIGRATE - Returns "Not Supported"
2. MIGRATE_INFO_TYPE - Return 2 i.e. Trusted OS is not present
3. MIGRATE_INFO_UP_CPU - Returns "Not Supported"
Signed-off-by: Anup Patel <anup.patel@linaro.org>
Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
This patch adds emulation of PSCI v0.2 AFFINITY_INFO function call
for KVM ARM/ARM64. This is a VCPU-level function call which will be
used to determine current state of given affinity level.
Signed-off-by: Anup Patel <anup.patel@linaro.org>
Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
The PSCI v0.2 SYSTEM_OFF and SYSTEM_RESET functions are system-level
functions hence cannot be fully emulated by in-kernel PSCI emulation code.
To tackle this, we forward PSCI v0.2 SYSTEM_OFF and SYSTEM_RESET function
calls from vcpu to user space (i.e. QEMU or KVMTOOL) via kvm_run structure
using KVM_EXIT_SYSTEM_EVENT exit reasons.
Signed-off-by: Anup Patel <anup.patel@linaro.org>
Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Currently, the kvm_psci_call() returns 'true' or 'false' based on whether
the PSCI function call was handled successfully or not. This does not help
us emulate system-level PSCI functions where the actual emulation work will
be done by user space (QEMU or KVMTOOL). Examples of such system-level PSCI
functions are: PSCI v0.2 SYSTEM_OFF and SYSTEM_RESET.
This patch updates kvm_psci_call() to return three types of values:
1) > 0 (success)
2) = 0 (success but exit to user space)
3) < 0 (errors)
Signed-off-by: Anup Patel <anup.patel@linaro.org>
Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Currently, the in-kernel PSCI emulation provides PSCI v0.1 interface to
VCPUs. This patch extends current in-kernel PSCI emulation to provide
PSCI v0.2 interface to VCPUs.
By default, ARM/ARM64 KVM will always provide PSCI v0.1 interface for
keeping the ABI backward-compatible.
To select PSCI v0.2 interface for VCPUs, the user space (i.e. QEMU or
KVMTOOL) will have to set KVM_ARM_VCPU_PSCI_0_2 feature when doing VCPU
init using KVM_ARM_VCPU_INIT ioctl.
Signed-off-by: Anup Patel <anup.patel@linaro.org>
Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
The current KVM implementation of PSCI returns INVALID_PARAMETERS if the
waitqueue for the corresponding CPU is not active. This does not seem
correct, since KVM should not care what the specific thread is doing,
for example, user space may not have called KVM_RUN on this VCPU yet or
the thread may be busy looping to user space because it received a
signal; this is really up to the user space implementation. Instead we
should check specifically that the CPU is marked as being turned off,
regardless of the VCPU thread state, and if it is, we shall
simply clear the pause flag on the CPU and wake up the thread if it
happens to be blocked for us.
Further, the implementation seems to be racy when executing multiple
VCPU threads. There really isn't a reasonable user space programming
scheme to ensure all secondary CPUs have reached kvm_vcpu_first_run_init
before turning on the boot CPU.
Therefore, set the pause flag on the vcpu at VCPU init time (which can
reasonably be expected to be completed for all CPUs by user space before
running any VCPUs) and clear both this flag and the feature (in case the
feature can somehow get set again in the future) and ping the waitqueue
on turning on a VCPU using PSCI.
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
- A couple a basic fixes for running BE guests on a LE host
- A performance improvement for overcommitted VMs (same as the equivalent
patch for ARM)
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Merge tag 'kvm-arm64/for-3.13-1' of git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms into kvm-next
A handful of fixes for KVM/arm64:
- A couple a basic fixes for running BE guests on a LE host
- A performance improvement for overcommitted VMs (same as the equivalent
patch for ARM)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Conflicts:
arch/arm/include/asm/kvm_emulate.h
arch/arm64/include/asm/kvm_emulate.h
When booting a vcpu using PSCI, make sure we start it with the
endianness of the caller. Otherwise, secondaries can be pretty
unhappy to execute a BE kernel in LE mode...
This conforms to PSCI spec Rev B, 5.13.3.
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
The KVM PSCI code blindly assumes that vcpu_id and MPIDR are
the same thing. This is true when vcpus are organized as a flat
topology, but is wrong when trying to emulate any other topology
(such as A15 clusters).
Change the KVM PSCI CPU_ON code to look at the MPIDR instead
of the vcpu_id to pick a target CPU.
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Currently, kvmtool unconditionally declares that HVC should be used
to call PSCI, so the function numbers in the DT tell the guest
nothing about the function ID namespace or calling convention for
SMC.
We already assume that the guest will examine and honour the DT,
since there is no way it could possibly guess the KVM-specific PSCI
function IDs otherwise. So let's not encourage guests to violate
what's specified in the DT by using SMC to make the call.
[ Modified to apply to top of kvm/arm tree - Christoffer ]
Signed-off-by: Dave P Martin <Dave.Martin@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@cs.columbia.edu>
Implement the PSCI specification (ARM DEN 0022A) to control
virtual CPUs being "powered" on or off.
PSCI/KVM is detected using the KVM_CAP_ARM_PSCI capability.
A virtual CPU can now be initialized in a "powered off" state,
using the KVM_ARM_VCPU_POWER_OFF feature flag.
The guest can use either SMC or HVC to execute a PSCI function.
Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <c.dall@virtualopensystems.com>
