RISC-V: KVM: fix vcpu vector context handling for kernel-mode vector

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Running vector workloads like perf + mcf on KVM can result in an
unexpected termination due to a vtype corruption. This happens because
the kernel-mode vector (KMV) misattributes the guest's vcpu context as
the user's context and source from a wrong status.VS.

The simplified call chain that results in this problem is shown as
follow:

__riscv_sys_ioctl()
    kvm_arch_vcpu_ioctl_run()
      kvm_riscv_vcpu_exit()
        kvm_riscv_vcpu_sbi_ecall()
          kvm_riscv_vcpu_pmu_ctr_stop()
            kvm_vcpu_write_guest()
              __copy_to_user()
                enter_vector_usercopy()
                  kernel_vector_begin()

kernel_vector_begin() should use the sstatus.VS from guest's vcpu
context instead of task_pt_reg(current). Also, it should not save
guest's v-reg into the user's context memory.

To resolve this, the vcpu context must be correctly saved when KMV is
serving a guest. However, invoking KVM functions directly from generic
RISC-V architecture code introduces a reverse dependency, breaking
builds when KVM is configured as N or M.

Address this by registering an RCU-protected callback for context
flushing. KVM registers this callback at module initialization and
unregisters it on exit. When KMV starts a kernel context, it can now
safely flush the vector context via the callback.

Fixes: ecd2ada8a5 ("riscv: Add support for kernel mode vector")
Signed-off-by: Andy Chiu <tchiu@tenstorrent.com>
Reviewed-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260803215250.824417-4-tchiu@tenstorrent.com
Signed-off-by: Anup Patel <anup@brainfault.org>

...

This commit is contained in:

Andy Chiu 2026-08-03 16:52:42 -05:00 • committed by Anup Patel

parent 848a973c5f

commit b5060a4aa3

7 changed files with 120 additions and 14 deletions

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24

arch/riscv/include/asm/kvm_vcpu_vector.h

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8

arch/riscv/include/asm/processor.h

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5

arch/riscv/include/asm/vector.h

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59

arch/riscv/kernel/kernel_mode_vector.c

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4

arch/riscv/kvm/main.c

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12

arch/riscv/kvm/vcpu.c

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22

arch/riscv/kvm/vcpu_vector.c

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