[PATCH v4] RISC-V: KVM: Delegate illegal instruction fault to VS mode

[Anup Patel]

On Mon, Jul 14, 2025 at 3:16 PM Xu Lu <luxu.kernel at bytedance.com> wrote:
>
> Delegate illegal instruction fault to VS mode by default to avoid such
> exceptions being trapped to HS and redirected back to VS.
>
> The delegation of illegal instruction fault is particularly important
> to guest applications that use vector instructions frequently. In such
> cases, an illegal instruction fault will be raised when guest user thread
> uses vector instruction the first time and then guest kernel will enable
> user thread to execute following vector instructions.
>
> The fw pmu event counter remains undeleted so that guest can still query
> illegal instruction events via sbi call. Guest will only see zero count
> on illegal instruction faults and know 'firmware' has delegated it.
>
> Signed-off-by: Xu Lu <luxu.kernel at bytedance.com>

LGTM.

Reviewed-by: Anup Patel <anup at brainfault.org>

Queued this patch for Linux-6.17

Thanks,
Anup

> ---
>  arch/riscv/include/asm/kvm_host.h | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
> index 85cfebc32e4cf..3f6b9270f366a 100644
> --- a/arch/riscv/include/asm/kvm_host.h
> +++ b/arch/riscv/include/asm/kvm_host.h
> @@ -44,6 +44,7 @@
>  #define KVM_REQ_STEAL_UPDATE           KVM_ARCH_REQ(6)
>
>  #define KVM_HEDELEG_DEFAULT            (BIT(EXC_INST_MISALIGNED) | \
> +                                        BIT(EXC_INST_ILLEGAL)     | \
>                                          BIT(EXC_BREAKPOINT)      | \
>                                          BIT(EXC_SYSCALL)         | \
>                                          BIT(EXC_INST_PAGE_FAULT) | \
> --
> 2.20.1
>