[PATCH] kvm: powerpc: book3s: Disable preemption while accessing paca xics_phys filed

[Michael Ellerman]

Denis Kirjanov <kda at linux-powerpc.org> writes:

> With CONFIG_DEBUG_PREEMPT enabled we see the following trace:
>
> [  129.314426] BUG: using smp_processor_id() in preemptible [00000000]
> code: modprobe/5459
> [  129.314580] caller is .kvmppc_book3s_init_hv+0x184/0x350 [kvm_hv]
> [  129.314697] CPU: 11 PID: 5459 Comm: modprobe Not tainted
> 4.11.0-rc3-00022-gc7e790c #1
> [  129.314848] Call Trace:
> [  129.314915] [c0000007d624b810] [c0000000023eef10] .dump_stack+0xe4/0x150 (unreliable)
> [  129.315065] [c0000007d624b8a0] [c000000001f6ec04] .check_preemption_disabled+0x134/0x150
> [  129.315210] [c0000007d624b940] [d00000000a010274] .kvmppc_book3s_init_hv+0x184/0x350 [kvm_hv]
> [  129.315339] [c0000007d624ba00] [c00000000191d5cc] .do_one_initcall+0x5c/0x1c0
> [  129.315416] [c0000007d624bad0] [c0000000023e9494] .do_init_module+0x84/0x240
> [  129.315492] [c0000007d624bb70] [c000000001aade18] .load_module+0x1f68/0x2a10
> [  129.315568] [c0000007d624bd20] [c000000001aaeb30] .SyS_finit_module+0xc0/0xf0
> [  129.315645] [c0000007d624be30] [c00000000191baec] system_call+0x38/0xfc
>
> Disable preemption while accessing paca struct to avoid inconsistent state
>
> Fixes: f725758 ("KVM: PPC: Book3S HV: Use OPAL XICS emulation on POWER9")
> Signed-off-by: Denis Kirjanov <kda at linux-powerpc.org>
> ---
>  arch/powerpc/kvm/book3s_hv.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 1ec86d9..8e96bab 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -3913,6 +3913,10 @@ static int kvmppc_radix_possible(void)
>  static int kvmppc_book3s_init_hv(void)
>  {
>  	int r;
> +#ifdef CONFIG_SMP
> +	unsigned long xics_phys;
> +#endif
> +
>  	/*
>  	 * FIXME!! Do we need to check on all cpus ?
>  	 */
> @@ -3930,7 +3934,11 @@ static int kvmppc_book3s_init_hv(void)
>  	 * indirectly, via OPAL.
>  	 */
>  #ifdef CONFIG_SMP
> -	if (!get_paca()->kvm_hstate.xics_phys) {
> +	preempt_disable();
> +	xics_phys = get_paca()->kvm_hstate.xics_phys;
> +	preempt_enable();
> +
> +	if (!xics_phys) {
>  		struct device_node *np;
  
Can you tell me what actual problem (other than the warning) this is
fixing?

cheers