Re: [PATCH v5 00/27] arm64: provide pseudo NMI with GICv3
From: Daniel Thompson
Date: Wed Aug 29 2018 - 07:37:43 EST
On Tue, Aug 28, 2018 at 04:51:10PM +0100, Julien Thierry wrote:
> This series is a continuation of the work started by Daniel . The goal
> is to use GICv3 interrupt priorities to simulate an NMI.
> The patches depend on the core API for NMIs patches .
As before... is there a git tree? With the NMI core API I think I might
be able to get some of my old pseudo-NMI demos working.
> To achieve this, set two priorities, one for standard interrupts and
> another, higher priority, for NMIs. Whenever we want to disable interrupts,
> we mask the standard priority instead so NMIs can still be raised. Some
> corner cases though still require to actually mask all interrupts
> effectively disabling the NMI.
> Daniel Thompson ran some benchmarks  on the previous version showing a
> small (<1%) performance drop when using interrupt priorities.
IMHO it is very important to disclose which micro-architecture (in this
case I think I was using C-A53 and GIC-500) the performance drop is
We know from both micro- and macro-benchmarks that the performance delta
is deeply dependant on core implementation. In fact, my own work in this
area stalled largely because the main device that justified my spending
working-hours on pseudo-NMI was too badly impacted to see it enabled by
> Currently, only PPIs and SPIs can be set as NMIs. IPIs being currently
> hardcoded IRQ numbers, there isn't a generic interface to set SGIs as NMI
> for now. LPIs being controlled by the ITS cannot be delivered as NMI.
> When an NMI is active on a CPU, no other NMI can be triggered on the CPU.
> Requirements to use this:
> - Have GICv3
> - SCR_EL3.FIQ is set to 1 when linux runs or have single security state
> - Select Kernel Feature -> Use ICC system registers for IRQ masking
> * Patches 1 to 3 aim at applying some alternatives early in the boot
> * Patches 4 to 7 ensure the logic of daifflags remains valid
> after arch_local_irq flags use ICC_PMR_EL1.
> * Patches 8 and 9 clean up GIC current priority definition to make it
> easier to introduce a new priority
> * Patches 10 to 16 prepare arch code for the use of priorities, saving and
> restoring ICC_PMR_EL1 appropriately
> * Patches 17 to 20 add the support to GICv3 driver to use priority masking
> if required by the architecture
> * Patches 21 to 23 make arm64 code use ICC_PMR_EL1 to enable/disable
> interrupts, leaving PSR.I as often as possible
> * Patches 24 to 27 add the support for NMIs to GICv3 driver
> Changes since V4:
> * Rebased to v4.19-rc1
> * Adapted GIC driver to the core NMI API
> * Added option to disable priority masking on command line
> * Added Daniel's Tested-by on patches related replacing PSR.I toggling with
> PMR masking
> * Fix scope matching for alternative features.
> * Spotted some more places using PSR.I or daif and replaced with generic
> interrupt functions
> Changes since V3:
> * Big refactoring. As suggested by Marc Z., some of the bigger patches
> needed to be split into smaller one.
> * Try to reduce the amount of #ifdef for the new feature by introducing
> an individual cpufeature for priority masking
> * Do not track which alternatives have been applied (was a bit dodgy
> anyway), and use an alternative for VHE cpu_enable callback
> * Fix a build failure with arm by adding the correct RPR accessors
> * Added Suggested-by tags for changes from comming or inspired by Daniel's
> series. Do let me know if you feel I missed something and am not giving
> you due credit.
> Changes since V2:
> * Series rebase to v4.17-rc6
> * Adapt pathces 1 and 2 to the rework of cpufeatures framework
> * Use the group0 detection scheme in the GICv3 driver to identify
> the priority view, and drop the use of a fake interrupt
> * Add the case for a GIC configured in a single security state
> * Use local_daif_restore instead of local_irq_enable the first time
> we enable interrupts after a bp hardening in the handling of a kernel
> entry. Otherwise PRS.I remains set...
> Changes since V1:
> * Series rebased to v4.15-rc8.
> * Check for arm64_early_features in this_cpu_has_cap (spotted by Suzuki).
> * Fix issue where debug exception were not masked when enabling debug in
> Changes since RFC:
> * The series was rebased to v4.15-rc2 which implied some changes mainly
> related to the work on exception entries and daif flags by James Morse.
> - The first patch in the previous series was dropped because no longer
> - With the semantics James introduced of "inheriting" daif flags,
> handling of PMR on exception entry is simplified as PMR is not altered
> by taking an exception and already inherited from previous state.
> - James pointed out that taking a PseudoNMI before reading the FAR_EL1
> register should not be allowed as per the TRM (D10.2.29):
> "FAR_EL1 is made UNKNOWN on an exception return from EL1."
> So in this submission PSR.I bit is cleared only after FAR_EL1 is read.
> * For KVM, only deal with PMR unmasking/restoring in common code, and VHE
> specific code makes sure PSR.I bit is set when necessary.
> * When detecting the GIC priority view (patch 5), wait for an actual
> interrupt instead of trying only once.
>  http://www.spinics.net/lists/arm-kernel/msg525077.html
>  https://lkml.org/lkml/2018/8/28/661
>  https://lkml.org/lkml/2018/7/20/803
>  https://lkml.org/lkml/2018/7/24/321
>  https://lkml.org/lkml/2018/5/21/276
>  https://lkml.org/lkml/2018/1/17/335
>  https://www.spinics.net/lists/arm-kernel/msg620763.html
>  https://www.spinics.net/lists/arm-kernel/msg610736.html
> Daniel Thompson (1):
> arm64: alternative: Apply alternatives early in boot process
> Julien Thierry (26):
> arm64: cpufeature: Set SYSREG_GIC_CPUIF as a boot system feature
> arm64: cpufeature: Use alternatives for VHE cpu_enable
> arm64: daifflags: Use irqflags functions for daifflags
> arm64: Use daifflag_restore after bp_hardening
> arm64: Delay daif masking for user return
> arm64: xen: Use existing helper to check interrupt status
> irqchip/gic: Unify GIC priority definitions
> irqchip/gic: Lower priority of GIC interrupts
> arm64: cpufeature: Add cpufeature for IRQ priority masking
> arm64: Make PMR part of task context
> arm64: Unmask PMR before going idle
> arm/arm64: gic-v3: Add helper functions to manage IRQ priorities
> arm64: kvm: Unmask PMR before entering guest
> arm64: irqflags: Use ICC_PMR_EL1 for interrupt masking
> arm64: daifflags: Include PMR in daifflags restore operations
> irqchip/gic-v3: Factor group0 detection into functions
> irqchip/gic-v3: Do not overwrite PMR value
> irqchip/gic-v3: Remove acknowledge loop
> irqchip/gic-v3: Switch to PMR masking after IRQ acknowledge
> arm64: Switch to PMR masking when starting CPUs
> arm64: Add build option for IRQ masking via priority
> arm64: Handle serror in NMI context
> irqchip/gic-v3: Detect current view of GIC priorities
> irqchip/gic-v3: Add base support for pseudo-NMI
> irqchip/gic: Add functions to access irq priorities
> irqchip/gic-v3: Allow interrupts to be set as pseudo-NMI
> Documentation/admin-guide/kernel-parameters.txt | 3 +
> Documentation/arm64/booting.txt | 5 +
> arch/arm/include/asm/arch_gicv3.h | 33 +++
> arch/arm64/Kconfig | 15 ++
> arch/arm64/include/asm/alternative.h | 3 +-
> arch/arm64/include/asm/arch_gicv3.h | 33 +++
> arch/arm64/include/asm/assembler.h | 17 +-
> arch/arm64/include/asm/cpucaps.h | 3 +-
> arch/arm64/include/asm/cpufeature.h | 2 +
> arch/arm64/include/asm/daifflags.h | 29 ++-
> arch/arm64/include/asm/efi.h | 3 +-
> arch/arm64/include/asm/irqflags.h | 100 +++++++--
> arch/arm64/include/asm/kvm_host.h | 12 +
> arch/arm64/include/asm/processor.h | 1 +
> arch/arm64/include/asm/ptrace.h | 13 +-
> arch/arm64/include/asm/xen/events.h | 2 +-
> arch/arm64/kernel/alternative.c | 28 ++-
> arch/arm64/kernel/asm-offsets.c | 1 +
> arch/arm64/kernel/cpufeature.c | 51 ++++-
> arch/arm64/kernel/entry.S | 63 +++++-
> arch/arm64/kernel/head.S | 35 +++
> arch/arm64/kernel/process.c | 2 +
> arch/arm64/kernel/smp.c | 12 +
> arch/arm64/kernel/traps.c | 8 +-
> arch/arm64/kvm/hyp/switch.c | 17 ++
> arch/arm64/mm/fault.c | 5 +-
> arch/arm64/mm/proc.S | 18 ++
> drivers/irqchip/irq-gic-common.c | 10 +
> drivers/irqchip/irq-gic-common.h | 2 +
> drivers/irqchip/irq-gic-v3-its.c | 2 +-
> drivers/irqchip/irq-gic-v3.c | 279 +++++++++++++++++++-----
> include/linux/irqchip/arm-gic-common.h | 6 +
> include/linux/irqchip/arm-gic.h | 5 -
> 33 files changed, 699 insertions(+), 119 deletions(-)