[PATCH v2 3/3] KVM: arm64: Limit clearing of ID_{AA64PFR0,PFR1}_EL1.GIC to userspace irqchip

[Mark Brown]

On Thu, Oct 30, 2025 at 12:27:07PM +0000, Marc Zyngier wrote:
> Now that the idreg's GIC field is in sync with the irqchip, limit
> the runtime clearing of these fields to the pathological case where
> we do not have an in-kernel GIC.
> 
> While we're at it, use the existing API instead of open-coded
> accessors to access the ID regs.

Today's next/pending-fixes is showing regressions on a range of physical
arm64 platforms (including at least a bunch of A53 systems, an A55 one
and an A72 one) in the steal_time selftest which bisect to this patch.
We get asserts in the kernel on ID register sets:

[  150.872407] WARNING: CPU: 0 PID: 2865 at arch/arm64/kvm/sys_regs.c:2353 kvm_set_vm_id_reg+0x9c/0xf4

...

[  151.045312] Call trace:
[  151.047780]  kvm_set_vm_id_reg+0x9c/0xf4 (P)
[  151.052098]  kvm_finalize_sys_regs+0x88/0x240
[  151.056504]  kvm_arch_vcpu_run_pid_change+0xb4/0x438
[  151.061527]  kvm_vcpu_ioctl+0x92c/0x9d0

which generate errors to userspace, causing the test to fail.  Full log
from one of the failing runs:

   https://lava.sirena.org.uk/scheduler/job/2065669#L2863

Bisect log:

# bad: [55f97faf872612ac604ae72eb1968e6619cc41be] Merge branch 'for-linux-next-fixes' of https://gitlab.freedesktop.org/drm/misc/kernel.git
# good: [f850568efe3a7a9ec4df357cfad1f997f0058924] Merge tag 'i2c-for-6.18-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux
# good: [636f4618b1cd96f6b5a2b8c7c4f665c8533ecf13] regulator: fixed: fix GPIO descriptor leak on register failure
# good: [86d57d9c07d54e8cb385ffe800930816ccdba0c1] spi: imx: keep dma request disabled before dma transfer setup
# good: [939edfaa10f1d22e6af6a84bf4bd96dc49c67302] spi: xilinx: increase number of retries before declaring stall
# good: [3cd2018e15b3d66d2187d92867e265f45ad79e6f] spi: Try to get ACPI GPIO IRQ earlier
# good: [29528c8e643bb0c54da01237a35010c6438423d2] ASoC: tas2781: fix getting the wrong device number
# good: [3dc8c73365d3ca25c99e7e1a0f493039d7291df5] ASoC: codecs: va-macro: fix resource leak in probe error path
# good: [84f5526e4dce0a44d050ceb1b1bf21d43016d91b] ASoC: tas2783A: Fix issues in firmware parsing
# good: [8da0efc3da9312b65f5cbf06e57d284f69222b2e] ASoC: doc: cs35l56: Update firmware filename description for B0 silicon
# good: [249d96b492efb7a773296ab2c62179918301c146] ASoC: da7213: Use component driver suspend/resume
git bisect start '55f97faf872612ac604ae72eb1968e6619cc41be' 'f850568efe3a7a9ec4df357cfad1f997f0058924' '636f4618b1cd96f6b5a2b8c7c4f665c8533ecf13' '86d57d9c07d54e8cb385ffe800930816ccdba0c1' '939edfaa10f1d22e6af6a84bf4bd96dc49c67302' '3cd2018e15b3d66d2187d92867e265f45ad79e6f' '29528c8e643bb0c54da01237a35010c6438423d2' '3dc8c73365d3ca25c99e7e1a0f493039d7291df5' '84f5526e4dce0a44d050ceb1b1bf21d43016d91b' '8da0efc3da9312b65f5cbf06e57d284f69222b2e' '249d96b492efb7a773296ab2c62179918301c146'
# test job: [636f4618b1cd96f6b5a2b8c7c4f665c8533ecf13] https://lava.sirena.org.uk/scheduler/job/2048731
# test job: [86d57d9c07d54e8cb385ffe800930816ccdba0c1] https://lava.sirena.org.uk/scheduler/job/2053555
# test job: [939edfaa10f1d22e6af6a84bf4bd96dc49c67302] https://lava.sirena.org.uk/scheduler/job/2057909
# test job: [3cd2018e15b3d66d2187d92867e265f45ad79e6f] https://lava.sirena.org.uk/scheduler/job/2049140
# test job: [29528c8e643bb0c54da01237a35010c6438423d2] https://lava.sirena.org.uk/scheduler/job/2057927
# test job: [3dc8c73365d3ca25c99e7e1a0f493039d7291df5] https://lava.sirena.org.uk/scheduler/job/2054782
# test job: [84f5526e4dce0a44d050ceb1b1bf21d43016d91b] https://lava.sirena.org.uk/scheduler/job/2053642
# test job: [8da0efc3da9312b65f5cbf06e57d284f69222b2e] https://lava.sirena.org.uk/scheduler/job/2038272
# test job: [249d96b492efb7a773296ab2c62179918301c146] https://lava.sirena.org.uk/scheduler/job/2043898
# test job: [55f97faf872612ac604ae72eb1968e6619cc41be] https://lava.sirena.org.uk/scheduler/job/2065669
# bad: [55f97faf872612ac604ae72eb1968e6619cc41be] Merge branch 'for-linux-next-fixes' of https://gitlab.freedesktop.org/drm/misc/kernel.git
git bisect bad 55f97faf872612ac604ae72eb1968e6619cc41be
# test job: [1f007059d445f5a1904328b3d34ad462329ba314] https://lava.sirena.org.uk/scheduler/job/2065857
# good: [1f007059d445f5a1904328b3d34ad462329ba314] Merge branch 'usb-linus' of https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
git bisect good 1f007059d445f5a1904328b3d34ad462329ba314
# test job: [0319e334a50bdc96486bca1f44828c55ea9d3008] https://lava.sirena.org.uk/scheduler/job/2066320
# good: [0319e334a50bdc96486bca1f44828c55ea9d3008] Merge branch 'reset/fixes' of https://git.pengutronix.de/git/pza/linux
git bisect good 0319e334a50bdc96486bca1f44828c55ea9d3008
# test job: [4fc9ec35871028dc4db558d1bb74f18075544a61] https://lava.sirena.org.uk/scheduler/job/2066361
# bad: [4fc9ec35871028dc4db558d1bb74f18075544a61] Merge branch 'dma-mapping-fixes' of https://git.kernel.org/pub/scm/linux/kernel/git/mszyprowski/linux.git
git bisect bad 4fc9ec35871028dc4db558d1bb74f18075544a61
# test job: [0e5ba55750c1f7fb194a0022b8c887e6413da9b1] https://lava.sirena.org.uk/scheduler/job/2066403
# good: [0e5ba55750c1f7fb194a0022b8c887e6413da9b1] Merge tag 'kvm-x86-fixes-6.18-rc5' of https://github.com/kvm-x86/linux into HEAD
git bisect good 0e5ba55750c1f7fb194a0022b8c887e6413da9b1
# test job: [ca00c3af8ede65d16097d322be330146d9231bd2] https://lava.sirena.org.uk/scheduler/job/2066412
# bad: [ca00c3af8ede65d16097d322be330146d9231bd2] Merge tag 'kvmarm-fixes-6.18-2' of git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEAD
git bisect bad ca00c3af8ede65d16097d322be330146d9231bd2
# test job: [103e17aac09cdd358133f9e00998b75d6c1f1518] https://lava.sirena.org.uk/scheduler/job/2066443
# good: [103e17aac09cdd358133f9e00998b75d6c1f1518] KVM: arm64: Check the untrusted offset in FF-A memory share
git bisect good 103e17aac09cdd358133f9e00998b75d6c1f1518
# test job: [50e7cce81b9b2fbd6f0104c1698959d45ce3cf58] https://lava.sirena.org.uk/scheduler/job/2066695
# bad: [50e7cce81b9b2fbd6f0104c1698959d45ce3cf58] KVM: arm64: Limit clearing of ID_{AA64PFR0,PFR1}_EL1.GIC to userspace irqchip
git bisect bad 50e7cce81b9b2fbd6f0104c1698959d45ce3cf58
# test job: [8a9866ff860052efc5f9766f3f87fae30c983156] https://lava.sirena.org.uk/scheduler/job/2067273
# good: [8a9866ff860052efc5f9766f3f87fae30c983156] KVM: arm64: Set ID_{AA64PFR0,PFR1}_EL1.GIC when GICv3 is configured
git bisect good 8a9866ff860052efc5f9766f3f87fae30c983156
# first bad commit: [50e7cce81b9b2fbd6f0104c1698959d45ce3cf58] KVM: arm64: Limit clearing of ID_{AA64PFR0,PFR1}_EL1.GIC to userspace irqchip
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