[PATCH v4 00/40] Optimize KVM/ARM for VHE systems

Christoffer Dall christoffer.dall at linaro.org
Thu Feb 15 13:02:52 PST 2018

This series redesigns parts of KVM/ARM to optimize the performance on
VHE systems.  The general approach is to try to do as little work as
possible when transitioning between the VM and the hypervisor.  This has
the benefit of lower latency when waiting for interrupts and delivering
virtual interrupts, and reduces the overhead of emulating behavior and
I/O in the host kernel.

Patches 01 through 06 are not VHE specific, but rework parts of KVM/ARM
that can be generally improved.  We then add infrastructure to move more
logic into vcpu_load and vcpu_put, we improve handling of VFP and debug

We then introduce a new world-switch function for VHE systems, which we
can tweak and optimize for VHE systems.  To do that, we rework a lot of
the system register save/restore handling and emulation code that may
need access to system registers, so that we can defer as many system
register save/restore operations to vcpu_load and vcpu_put, and move
this logic out of the VHE world switch function.

We then optimize the configuration of traps.  On non-VHE systems, both
the host and VM kernels run in EL1, but because the host kernel should
have full access to the underlying hardware, but the VM kernel should
not, we essentially make the host kernel more privileged than the VM
kernel despite them both running at the same privilege level by enabling
VE traps when entering the VM and disabling those traps when exiting the
VM.  On VHE systems, the host kernel runs in EL2 and has full access to
the hardware (as much as allowed by secure side software), and is
unaffected by the trap configuration.  That means we can configure the
traps for VMs running in EL1 once, and don't have to switch them on and
off for every entry/exit to/from the VM.

Finally, we improve our VGIC handling by moving all save/restore logic
out of the VHE world-switch, and we make it possible to truly only
evaluate if the AP list is empty and not do *any* VGIC work if that is
the case, and only do the minimal amount of work required in the course
of the VGIC processing when we have virtual interrupts in flight.

The patches are based on v4.16-rc1 with a fix for userspace irqchips and a
patch from Dave Martin that moves CPU ID register traps out of the world

I've given the patches a fair amount of testing on Thunder-X, Mustang,
Seattle, and TC2 (32-bit) for non-VHE testing, and tested VHE
functionality on TX2.

The patches are also available in the vhe-optimize-v4 branch on my
kernel.org repository [1].  The vhe-optimize-v4-base branch contains
prerequisites of this series.

Changes since v3:
 - Rebased on v4.16-rc1 (fun!)
 - Removed VFP optimizations because it was discovered that the deferred
   approach taken in v3 was buggy
   This causes a fair amount of changes throughout and I've removed
   affected reviewed-by and other tags as best I could to take this into
 - Used a switch-statement to handle deferred system registers instead
   of the macro approach taken in v3.
 - Addressed other review coments (tried to keep track of this with logs
   of changes in individual patches).
 - I ran Yury's IPI benchark test and other tests on TX2 and could not
   observe a performance regression, but rather an improvement of around
   65%.  I suspect the previous regression was due to the timer WFI
   problem solved for v4.16-rc1.
 - I haven't included Tomasz' reviewed-by, because I figured too much of
   the series has changed since v3.

Changes since v2:
 - Rebased on v4.15-rc3.
 - Includes two additional patches that only does vcpu_load after
   kvm_vcpu_first_run_init and only for KVM_RUN.
 - Addressed review comments from v2 (detailed changelogs are in the
   individual patches).


[1]: git://git.kernel.org/pub/scm/linux/kernel/git/cdall/linux.git vhe-optimize-v4

Christoffer Dall (39):
  KVM: arm/arm64: Avoid vcpu_load for other vcpu ioctls than KVM_RUN
  KVM: arm/arm64: Move vcpu_load call after kvm_vcpu_first_run_init
  KVM: arm64: Avoid storing the vcpu pointer on the stack
  KVM: arm64: Rework hyp_panic for VHE and non-VHE
  KVM: arm/arm64: Get rid of vcpu->arch.irq_lines
  KVM: arm/arm64: Add kvm_vcpu_load_sysregs and kvm_vcpu_put_sysregs
  KVM: arm/arm64: Introduce vcpu_el1_is_32bit
  KVM: arm64: Move debug dirty flag calculation out of world switch
  KVM: arm64: Slightly improve debug save/restore functions
  KVM: arm64: Improve debug register save/restore flow
  KVM: arm64: Factor out fault info population and gic workarounds
  KVM: arm64: Introduce VHE-specific kvm_vcpu_run
  KVM: arm64: Remove kern_hyp_va() use in VHE switch function
  KVM: arm64: Don't deactivate VM on VHE systems
  KVM: arm64: Remove noop calls to timer save/restore from VHE switch
  KVM: arm64: Move userspace system registers into separate function
  KVM: arm64: Rewrite sysreg alternatives to static keys
  KVM: arm64: Introduce separate VHE/non-VHE sysreg save/restore
  KVM: arm/arm64: Remove leftover comment from kvm_vcpu_run_vhe
  KVM: arm64: Unify non-VHE host/guest sysreg save and restore functions
  KVM: arm64: Don't save the host ELR_EL2 and SPSR_EL2 on VHE systems
  KVM: arm64: Change 32-bit handling of VM system registers
  KVM: arm64: Rewrite system register accessors to read/write functions
  KVM: arm64: Introduce framework for accessing deferred sysregs
  KVM: arm/arm64: Prepare to handle deferred save/restore of SPSR_EL1
  KVM: arm64: Prepare to handle deferred save/restore of ELR_EL1
  KVM: arm64: Defer saving/restoring 64-bit sysregs to vcpu load/put on
  KVM: arm64: Prepare to handle deferred save/restore of 32-bit
  KVM: arm64: Defer saving/restoring 32-bit sysregs to vcpu load/put
  KVM: arm64: Move common VHE/non-VHE trap config in separate functions
  KVM: arm64: Directly call VHE and non-VHE FPSIMD enabled functions
  KVM: arm64: Configure c15, PMU, and debug register traps on cpu
    load/put for VHE
  KVM: arm64: Cleanup __activate_traps and __deactive_traps for VHE and
  KVM: arm/arm64: Get rid of vgic_elrsr
  KVM: arm/arm64: Handle VGICv2 save/restore from the main VGIC code
  KVM: arm/arm64: Move arm64-only vgic-v2-sr.c file to arm64
  KVM: arm/arm64: Handle VGICv3 save/restore from the main VGIC code on
  KVM: arm/arm64: Move VGIC APR save/restore to vgic put/load
  KVM: arm/arm64: Avoid VGICv3 save/restore on VHE with no IRQs

Shih-Wei Li (1):
  KVM: arm64: Move HCR_INT_OVERRIDE to default HCR_EL2 guest flag

 arch/arm/include/asm/kvm_asm.h                    |   5 +-
 arch/arm/include/asm/kvm_emulate.h                |  21 +-
 arch/arm/include/asm/kvm_host.h                   |   6 +-
 arch/arm/include/asm/kvm_hyp.h                    |   4 +
 arch/arm/kvm/emulate.c                            |   4 +-
 arch/arm/kvm/hyp/Makefile                         |   1 -
 arch/arm/kvm/hyp/switch.c                         |  16 +-
 arch/arm64/include/asm/kvm_arm.h                  |   4 +-
 arch/arm64/include/asm/kvm_asm.h                  |  18 +-
 arch/arm64/include/asm/kvm_emulate.h              |  74 +++--
 arch/arm64/include/asm/kvm_host.h                 |  46 ++-
 arch/arm64/include/asm/kvm_hyp.h                  |  29 +-
 arch/arm64/include/asm/kvm_mmu.h                  |   2 +-
 arch/arm64/kernel/asm-offsets.c                   |   1 +
 arch/arm64/kvm/debug.c                            |  28 +-
 arch/arm64/kvm/guest.c                            |   3 -
 arch/arm64/kvm/hyp/Makefile                       |   2 +-
 arch/arm64/kvm/hyp/debug-sr.c                     |  88 ++---
 arch/arm64/kvm/hyp/entry.S                        |   6 +-
 arch/arm64/kvm/hyp/hyp-entry.S                    |  31 +-
 arch/arm64/kvm/hyp/switch.c                       | 373 +++++++++++++---------
 arch/arm64/kvm/hyp/sysreg-sr.c                    | 172 ++++++++--
 {virt/kvm/arm => arch/arm64/kvm}/hyp/vgic-v2-sr.c |  81 -----
 arch/arm64/kvm/inject_fault.c                     |  24 +-
 arch/arm64/kvm/regmap.c                           |  67 +++-
 arch/arm64/kvm/sys_regs.c                         | 166 +++++++---
 arch/arm64/kvm/sys_regs.h                         |   4 +-
 arch/arm64/kvm/sys_regs_generic_v8.c              |   4 +-
 include/kvm/arm_vgic.h                            |   2 -
 virt/kvm/arm/aarch32.c                            |   2 +-
 virt/kvm/arm/arch_timer.c                         |   4 -
 virt/kvm/arm/arm.c                                |  50 ++-
 virt/kvm/arm/hyp/timer-sr.c                       |  44 +--
 virt/kvm/arm/hyp/vgic-v3-sr.c                     | 244 ++++++++------
 virt/kvm/arm/mmu.c                                |   6 +-
 virt/kvm/arm/pmu.c                                |  37 +--
 virt/kvm/arm/vgic/vgic-init.c                     |  11 -
 virt/kvm/arm/vgic/vgic-v2.c                       |  61 +++-
 virt/kvm/arm/vgic/vgic-v3.c                       |  12 +-
 virt/kvm/arm/vgic/vgic.c                          |  21 ++
 virt/kvm/arm/vgic/vgic.h                          |   3 +
 41 files changed, 1104 insertions(+), 673 deletions(-)
 rename {virt/kvm/arm => arch/arm64/kvm}/hyp/vgic-v2-sr.c (51%)


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