Re: [PATCH v4 09/18] KVM: arm64: Introduce __pkvm_vcpu_{load,put}()

[Mark Brown <broonie@kernel.org>]

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On Wed, Dec 18, 2024 at 07:40:50PM +0000, Quentin Perret wrote:
> From: Marc Zyngier <maz@kernel.org>
> 
> Rather than look-up the hyp vCPU on every run hypercall at EL2,
> introduce a per-CPU 'loaded_hyp_vcpu' tracking variable which is updated
> by a pair of load/put hypercalls called directly from
> kvm_arch_vcpu_{load,put}() when pKVM is enabled.

Current mainline crashes when running the arch_timer_edge_cases selftest
in pKVM mode on a LibreTech Le Potato board, with a bisection pointing
at this change.  The system dies like this:

# selftests: kvm: arch_timer_edge_cases
[  130.599140] kvm [4518]: nVHE hyp panic at: [<ffff800081102b58>] __kvm_nvhe___vgic_v3_restore_vmcr_aprs+0x8/0x84!
[  130.603685] kvm [4518]: Cannot dump pKVM nVHE stacktrace: !CONFIG_PROTECTED_NVHE_STACKTRACE
[  130.611962] kvm [4518]: Hyp Offset: 0xfffeca95ed000000
[  130.617053] Kernel panic - not syncing: HYP panic:

Full log:

   https://lava.sirena.org.uk/scheduler/job/1092083

Bisection log:

git bisect start
# status: waiting for both good and bad commits
# bad: [2014c95afecee3e76ca4a56956a936e23283f05b] Linux 6.14-rc1
git bisect bad 2014c95afecee3e76ca4a56956a936e23283f05b
# status: waiting for good commit(s), bad commit known
# good: [ffd294d346d185b70e28b1a28abe367bbfe53c04] Linux 6.13
git bisect good ffd294d346d185b70e28b1a28abe367bbfe53c04
# good: [6250ebe666e425e173df5e11e8a612d57921f48d] i2c: Fix core-managed per-client debugfs handling
git bisect good 6250ebe666e425e173df5e11e8a612d57921f48d
# good: [647d69605c70368d54fc012fce8a43e8e5955b04] Merge tag 'pci-v6.14-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/pci/pci
git bisect good 647d69605c70368d54fc012fce8a43e8e5955b04
# good: [13845bdc869f136f92ad3d40ea09b867bb4ce467] Merge tag 'char-misc-6.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc
git bisect good 13845bdc869f136f92ad3d40ea09b867bb4ce467
# bad: [9f10e7fb6a06bce4f81de5fd0f2f0390f99e89e4] Merge tag 'phy-for-6.14' of git://git.kernel.org/pub/scm/linux/kernel/git/phy/linux-phy
git bisect bad 9f10e7fb6a06bce4f81de5fd0f2f0390f99e89e4
# bad: [58f504efcda54a9079a38203acc088c3354aaa60] Merge tag 'tty-6.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty
git bisect bad 58f504efcda54a9079a38203acc088c3354aaa60
# good: [a37eea94f775132866ecdd466fd88027d7125515] Merge tag 'sparc-for-6.14-tag1' of git://git.kernel.org/pub/scm/linux/kernel/git/alarsson/linux-sparc
git bisect good a37eea94f775132866ecdd466fd88027d7125515
# bad: [5e68d2eeac70978a06406c5b156815ceb00437f9] Merge branch kvm-arm64/pkvm-memshare-declutter into kvmarm-master/next
git bisect bad 5e68d2eeac70978a06406c5b156815ceb00437f9
# bad: [d0670128d42fa170bf8ba878cd23504c5c5cccc7] Merge branch kvm-arm64/pkvm-np-guest into kvmarm-master/next
git bisect bad d0670128d42fa170bf8ba878cd23504c5c5cccc7
# good: [c4a6ed85455979ef3fbadc2f1bdf18734b0ecea6] KVM: arm64: Promote guest ownership for DBGxVR/DBGxCR reads
git bisect good c4a6ed85455979ef3fbadc2f1bdf18734b0ecea6
# bad: [d0bd3e6570aee42766e7bd884734ae078667ea1e] KVM: arm64: Introduce __pkvm_host_share_guest()
git bisect bad d0bd3e6570aee42766e7bd884734ae078667ea1e
# good: [5398ddc5c90bd418b90d859e9267aa39399021af] KVM: arm64: Pass walk flags to kvm_pgtable_stage2_mkyoung
git bisect good 5398ddc5c90bd418b90d859e9267aa39399021af
# good: [c77e5181fed54b25d489eb7d2ccb5c1c72a1063c] KVM: arm64: Make kvm_pgtable_stage2_init() a static inline function
git bisect good c77e5181fed54b25d489eb7d2ccb5c1c72a1063c
# bad: [f7d03fcbf1f482069e9afac55b17de3bd323b8f6] KVM: arm64: Introduce __pkvm_vcpu_{load,put}()
git bisect bad f7d03fcbf1f482069e9afac55b17de3bd323b8f6
# good: [99996d575ee69d4327bad98a0148729b73dde23a] KVM: arm64: Add {get,put}_pkvm_hyp_vm() helpers
git bisect good 99996d575ee69d4327bad98a0148729b73dde23a
# first bad commit: [f7d03fcbf1f482069e9afac55b17de3bd323b8f6] KVM: arm64: Introduce __pkvm_vcpu_{load,put}()

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