Re: [PATCH] RISC-V: KVM: Teardown riscv specific bits after kvm_exit

[Sean Christopherson]

On Mon, Mar 17, 2025, Atish Patra wrote:
> During a module removal, kvm_exit invokes arch specific disable
> call which disables AIA. However, we invoke aia_exit before kvm_exit
> resulting in the following warning. KVM kernel module can't be inserted
> afterwards due to inconsistent state of IRQ.
> 
> [25469.031389] percpu IRQ 31 still enabled on CPU0!
> [25469.031732] WARNING: CPU: 3 PID: 943 at kernel/irq/manage.c:2476 __free_percpu_irq+0xa2/0x150
> [25469.031804] Modules linked in: kvm(-)
> [25469.031848] CPU: 3 UID: 0 PID: 943 Comm: rmmod Not tainted 6.14.0-rc5-06947-g91c763118f47-dirty #2
> [25469.031905] Hardware name: riscv-virtio,qemu (DT)
> [25469.031928] epc : __free_percpu_irq+0xa2/0x150
> [25469.031976]  ra : __free_percpu_irq+0xa2/0x150
> [25469.032197] epc : ffffffff8007db1e ra : ffffffff8007db1e sp : ff2000000088bd50
> [25469.032241]  gp : ffffffff8131cef8 tp : ff60000080b96400 t0 : ff2000000088baf8
> [25469.032285]  t1 : fffffffffffffffc t2 : 5249207570637265 s0 : ff2000000088bd90
> [25469.032329]  s1 : ff60000098b21080 a0 : 037d527a15eb4f00 a1 : 037d527a15eb4f00
> [25469.032372]  a2 : 0000000000000023 a3 : 0000000000000001 a4 : ffffffff8122dbf8
> [25469.032410]  a5 : 0000000000000fff a6 : 0000000000000000 a7 : ffffffff8122dc10
> [25469.032448]  s2 : ff60000080c22eb0 s3 : 0000000200000022 s4 : 000000000000001f
> [25469.032488]  s5 : ff60000080c22e00 s6 : ffffffff80c351c0 s7 : 0000000000000000
> [25469.032582]  s8 : 0000000000000003 s9 : 000055556b7fb490 s10: 00007ffff0e12fa0
> [25469.032621]  s11: 00007ffff0e13e9a t3 : ffffffff81354ac7 t4 : ffffffff81354ac7
> [25469.032664]  t5 : ffffffff81354ac8 t6 : ffffffff81354ac7
> [25469.032698] status: 0000000200000100 badaddr: ffffffff8007db1e cause: 0000000000000003
> [25469.032738] [<ffffffff8007db1e>] __free_percpu_irq+0xa2/0x150
> [25469.032797] [<ffffffff8007dbfc>] free_percpu_irq+0x30/0x5e
> [25469.032856] [<ffffffff013a57dc>] kvm_riscv_aia_exit+0x40/0x42 [kvm]
> [25469.033947] [<ffffffff013b4e82>] cleanup_module+0x10/0x32 [kvm]
> [25469.035300] [<ffffffff8009b150>] __riscv_sys_delete_module+0x18e/0x1fc
> [25469.035374] [<ffffffff8000c1ca>] syscall_handler+0x3a/0x46
> [25469.035456] [<ffffffff809ec9a4>] do_trap_ecall_u+0x72/0x134
> [25469.035536] [<ffffffff809f5e18>] handle_exception+0x148/0x156
> 
> Invoke aia_exit and other arch specific cleanup functions after kvm_exit
> so that disable gets a chance to be called first before exit.
> 
> Fixes: 54e43320c2ba ("RISC-V: KVM: Initial skeletal support for AIA")
> 
> Signed-off-by: Atish Patra <atishp@xxxxxxxxxxxx>
> ---

FWIW,

Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>

>  arch/riscv/kvm/main.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/kvm/main.c b/arch/riscv/kvm/main.c
> index 1fa8be5ee509..4b24705dc63a 100644
> --- a/arch/riscv/kvm/main.c
> +++ b/arch/riscv/kvm/main.c
> @@ -172,8 +172,8 @@ module_init(riscv_kvm_init);
>  
>  static void __exit riscv_kvm_exit(void)
>  {
> -	kvm_riscv_teardown();
> -
>  	kvm_exit();
> +
> +	kvm_riscv_teardown();

I wonder if there's a way we can guard against kvm_init()/kvm_exit() being called
too early/late.  x86 had similar bugs for a very long time, e.g. see commit
e32b120071ea ("KVM: VMX: Do _all_ initialization before exposing /dev/kvm to userspace").

E.g. maybe we do something like create+destroy a VM at the end of kvm_init() and
the beginning of kvm_exit()?  Not sure if that would work for kvm_exit(), but it
should definitely be fine for kvm_init().

It wouldn't prevent bugs, but maybe it would help detect them during development?