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Date:   Fri, 25 May 2018 11:16:32 +0100
From:   Daniel Thompson <daniel.thompson@linaro.org>
To:     Julien Thierry <julien.thierry@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        joel@joelfernandes.org, marc.zyngier@arm.com, mark.rutland@arm.com,
        christoffer.dall@arm.com, james.morse@arm.com,
        catalin.marinas@arm.com, will.deacon@arm.com
Subject: Re: [PATCH v4 00/26] arm64: provide pseudo NMI with GICv3
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On Fri, May 25, 2018 at 10:49:06AM +0100, Julien Thierry wrote:
> This series is a continuation of the work started by Daniel [1]. The goal
> is to use GICv3 interrupt priorities to simulate an NMI.
> 
> 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.
> 
> 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. I don't think there is any reason LPIs should be allowed to be set
> as NMI as they do not have an active state.
> When an NMI is active on a CPU, no other NMI can be triggered on the CPU.
> 
> After the big refactoring I get performances similar to the ones I had
> in v3[2], reposting old results here:
> 
> - "hackbench 200 process 1000" (average over 20 runs)
> +-----------+----------+------------+------------------+
> |           | native   | PMR guest  | v4.17-rc6 guest  |
> +-----------+----------+------------+------------------+
> | PMR host  | 40.0336s |   39.3039s |         39.2044s |
> | v4.17-rc6 | 40.4040s |   39.6011s |         39.1147s |
> +-----------+----------+------------+------------------+
> 
> - Kernel build from defconfig:
> PMR host:  13m45.743s
> v4.17-rc6: 13m40.400s
> 
> I'll try to post more detailed benchmarks later if I find notable
> differences with the previous version.

Do you have a public git tree anywhere... I *can* apply 26 patches from
e-mail but I'd rather pull them!


Daniel.

> 
> 
> 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 4 aim at applying some alternatives early in the boot
>   process, including the feature for priority masking.
> 
> * Patches 5 to 7 and 17 lightly refactor bits of GIC driver to make things
>   nicer for the rest of the series.
> 
> * Patches 8 to 10 and 16 ensure the logic of daifflags remains valid
>   after arch_local_irq flags use ICC_PMR_EL1.
> 
> * Patches 11 to 14 do some required PMR treatement in order for things to
>   work when the system uses priority masking.
> 
> * Patches 15, 18, 19, 20 and 21 actually make the changes to use
>   ICC_PMR_EL1 for priority masking/unmasking when disabling/enabling
>   interrupts.
> 
> * Patches 22 to 26 provide support for pseudo-NMI in the GICv3 driver
>   when priority masking is enabled.
> 
> 
> Changes since V3[2]:
> * 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[3]:
> * 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[4]:
> * 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
>   mdscr_el1.
> 
> Changes since RFC[5]:
> * 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
>     applicable.
> 
>   - 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.
> 
> 
> [1] http://www.spinics.net/lists/arm-kernel/msg525077.html
> [2] https://lkml.org/lkml/2018/5/21/276
> [3] https://lkml.org/lkml/2018/1/17/335
> [4] https://www.spinics.net/lists/arm-kernel/msg620763.html
> [5] https://www.spinics.net/lists/arm-kernel/msg610736.html
> 
> Cheers,
> 
> Julien
> 
> -->
> 
> Daniel Thompson (1):
>   arm64: alternative: Apply alternatives early in boot process
> 
> Julien Thierry (25):
>   arm64: cpufeature: Set SYSREG_GIC_CPUIF as a boot system feature
>   arm64: cpufeature: Add cpufeature for IRQ priority masking
>   arm64: cpufeature: Use alternatives for VHE cpu_enable
>   irqchip/gic: Unify GIC priority definitions
>   irqchip/gic: Lower priority of GIC interrupts
>   irqchip/gic-v3: Remove acknowledge loop
>   arm64: daifflags: Use irqflags functions for daifflags
>   arm64: Use daifflag_restore after bp_hardening
>   arm64: Delay daif masking for user return
>   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: 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: Detect current view of GIC priorities
>   irqchip/gic: Add functions to access irq priorities
>   irqchip/gic-v3: Add base support for pseudo-NMI
>   irqchip/gic-v3: Provide NMI handlers
>   irqchip/gic-v3: Allow interrupts to be set as pseudo-NMI
> 
>  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    |  32 ++++
>  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     |  32 ++--
>  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/kernel/alternative.c        |  30 +++-
>  arch/arm64/kernel/asm-offsets.c        |   1 +
>  arch/arm64/kernel/cpufeature.c         |  35 +++-
>  arch/arm64/kernel/entry.S              |  67 ++++++-
>  arch/arm64/kernel/head.S               |  35 ++++
>  arch/arm64/kernel/process.c            |   2 +
>  arch/arm64/kernel/smp.c                |  12 ++
>  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           | 318 +++++++++++++++++++++++++++------
>  include/linux/interrupt.h              |   1 +
>  include/linux/irqchip/arm-gic-common.h |   6 +
>  include/linux/irqchip/arm-gic.h        |   5 -
>  31 files changed, 719 insertions(+), 118 deletions(-)
> 
> --
> 1.9.1