[PATCH v4 0/3] RISC-V: KVM: fix vcpu vector context handling

This series fixes a vtype corruption encountered when running perf +
vector workload on KVM.

The root cause of the bug is that the kernel-mode vector (KMV)
misattributes the guest's vcpu context as the user's context. To solve
this, we need to correctly save the vcpu context when the kernel-mode
vector is serving a guest.

However, calling directly into KVM from RISC-V generic architecture code
creates a reverse dependency, which is problematic when KVM is built as
a module. To address this, we introduce an RCU-protected callback for
context flushing, which KVM registers during module init.

Patch 1 is a preparatory cleanup that refactors
riscv_v_start_kernel_context().
Patch 2 prepares get/put_cpu_vector_context() for gaurding the use of
vector in kvm_arch_vcpu_load/put()
Patch 3 implements the callback mechanism and fixes the context handling.

Patch summary:
 - unchanged patch: 1, 3
 - new patch: none
 - modified patch: 2

Changelog v4:
 - Include a header to solve a mid-series build fail (patchwork ci)
 - Drop preempt_v_started test in may_use_simd (Sashiko)
 - Link to v3: https://lore.kernel.org/all/[email protected]/

Changelog v3:
 - Limit the export scope for {get,put}_cpu_vector_context()
 - clears RISCV_V_VCPU_NEED_RESTORE flag in host restore to prevent
   leaking
 - consolidates guest vector restore at returning to guest to prevent
   unnecessary save/restore between the preemptible window from
   vcpu_load to vcpu_enter_exit
 - Document flags added to riscv_v_flags
 - Link to v2: https://lore.kernel.org/all/[email protected]/

Changelog v2:
 - Address issues pointed out by sashiko (2, 3)
 - Link to v1: https://lore.kernel.org/all/[email protected]/

Andy Chiu (3):
  riscv: vector: refactor riscv_v_start_kernel_context
  riscv: vector: allow non-preemptible kernel-mode vector with IRQs off
  RISC-V: KVM: fix vcpu vector context handling for kernel-mode vector

 arch/riscv/include/asm/kvm_vcpu_vector.h | 24 +++++++
 arch/riscv/include/asm/processor.h       |  8 +++
 arch/riscv/include/asm/simd.h            | 16 +----
 arch/riscv/include/asm/vector.h          |  5 ++
 arch/riscv/kernel/kernel_mode_vector.c   | 80 ++++++++++++++++--------
 arch/riscv/kvm/main.c                    |  4 ++
 arch/riscv/kvm/vcpu.c                    | 12 ++++
 arch/riscv/kvm/vcpu_vector.c             | 22 ++++++-
 8 files changed, 131 insertions(+), 40 deletions(-)

-- 
2.43.0


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