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Will Deacon 28b82be094 KVM: arm64: Fix kernel BUG() due to bad backport of FPSIMD/SVE/SME fix Upstream commit `fbc7e61195` ("KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state") relies on interrupts being disabled during fpsimd_save_and_flush_cpu_state() so that a softirq cannot be taken while the host floating point context is being saved and potentially try to use kernel-mode NEON. Unfortunately, stable kernels without `9b19700e62` ("arm64: fpsimd: Drop unneeded 'busy' flag") leave interrupts enabled in fpsimd_save_and_flush_cpu_state() and so the BUG_ON(!may_use_simd()) in kernel_neon_begin() has been observed to trigger in real-world usage: \| kernel BUG at arch/arm64/kernel/fpsimd.c:1904! \| Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP \| \| Call trace: \| kernel_neon_begin+0xdc/0x12c \| ... \| crypto_aead_decrypt+0x5c/0x6c \| seqiv_aead_decrypt+0x88/0x9c \| crypto_aead_decrypt+0x5c/0x6c \| esp_input+0x280/0x364 \| xfrm_input+0x6ac/0x16f8 \| ... \| net_rx_action+0x13c/0x31c \| handle_softirqs+0x124/0x3d0 \| __do_softirq+0x14/0x20 \| ____do_softirq+0x10/0x20 \| call_on_irq_stack+0x3c/0x74 \| do_softirq_own_stack+0x1c/0x2c \| __irq_exit_rcu+0x54/0xb4 \| irq_exit_rcu+0x10/0x1c \| el1_interrupt+0x38/0x58 \| el1h_64_irq_handler+0x18/0x24 \| el1h_64_irq+0x68/0x6c \| fpsimd_save+0xe4/0x130 \| kvm_arch_vcpu_load_fp+0x2c/0x58 \| kvm_arch_vcpu_load+0x88/0x26c \| kvm_sched_in+0x2c/0x3c Given that `9b19700e62` ("arm64: fpsimd: Drop unneeded 'busy' flag") is not a fix in its own right, has non-trivial dependencies and is a reasonably invasive change to the in-kernel use of fpsimd, opt instead for a simple fix to use the softirq-safe {get,put}_cpu_fpsimd_context() helpers in fpsimd_save_and_flush_cpu_state(). Cc: Ard Biesheuvel <ardb@kernel.org> Cc: Lee Jones <lee@kernel.org> Cc: Sasha Levin <sashal@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Fuad Tabba <tabba@google.com> Cc: Marc Zyngier <maz@kernel.org> Cc: <stable@vger.kernel.org> # 5.15.y, 6.1.y and 6.6.y Fixes: `806d5c1e1d` ("KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state") # 6.6.y Fixes: `04c50cc23a` ("KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state") # 6.1.y Fixes: `5289ac43b6` ("KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state") # 5.15.y Signed-off-by: Will Deacon <will@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2025-08-28 16:28:43 +02:00
arch	KVM: arm64: Fix kernel BUG() due to bad backport of FPSIMD/SVE/SME fix	2025-08-28 16:28:43 +02:00
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drivers	topology: Set capacity_freq_ref in all cases	2025-08-28 16:28:42 +02:00
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include	arm64/amu: Use capacity_ref_freq() to set AMU ratio	2025-08-28 16:28:42 +02:00
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kernel	sched/fair: Fix frequency selection for non-invariant case	2025-08-28 16:28:43 +02:00
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Makefile	kbuild: userprogs: use correct linker when mixing clang and GNU ld	2025-08-28 16:28:42 +02:00
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README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.