Re: [PATCH 4/8] KVM: PPC: Book3S HV: Ratelimit machine check messages coming from guests

[Michael Ellerman]

Nicholas Piggin <npig...@gmail.com> writes:
> A number of machine check exceptions are triggerable by the guest.
> Ratelimit these to avoid a guest flooding the host console and logs.
>
> Signed-off-by: Nicholas Piggin <npig...@gmail.com>
> ---
>  arch/powerpc/kvm/book3s_hv.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index e3b1839fc251..c94f9595133d 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -1328,8 +1328,12 @@ static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
>               r = RESUME_GUEST;
>               break;
>       case BOOK3S_INTERRUPT_MACHINE_CHECK:
> -             /* Print the MCE event to host console. */
> -             machine_check_print_event_info(&vcpu->arch.mce_evt, false, 
> true);
> +             /*
> +              * Print the MCE event to host console. Ratelimit so the guest
> +              * can't flood the host log.
> +              */
> +             if (printk_ratelimit())
> +                     
> machine_check_print_event_info(&vcpu->arch.mce_evt,false, true);

You're not supposed to use printk_ratelimit(), because there's a single
rate limit state for all printks. ie. some other noisty printk() can
cause this one to never be printed.

I folded this in:

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index cbbc4f0a26fe..cfaa91b27112 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1327,12 +1327,14 @@ static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
        case BOOK3S_INTERRUPT_SYSTEM_RESET:
                r = RESUME_GUEST;
                break;
-       case BOOK3S_INTERRUPT_MACHINE_CHECK:
+       case BOOK3S_INTERRUPT_MACHINE_CHECK: {
+               static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL,
+                                             DEFAULT_RATELIMIT_BURST);
                /*
                 * Print the MCE event to host console. Ratelimit so the guest
                 * can't flood the host log.
                 */
-               if (printk_ratelimit())
+               if (__ratelimit(&rs))
                        
machine_check_print_event_info(&vcpu->arch.mce_evt,false, true);
 
                /*
@@ -1361,6 +1363,7 @@ static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
 
                r = RESUME_HOST;
                break;
+       }
        case BOOK3S_INTERRUPT_PROGRAM:
        {
                ulong flags;
@@ -1520,12 +1523,16 @@ static int kvmppc_handle_nested_exit(struct kvm_vcpu 
*vcpu)
                r = RESUME_GUEST;
                break;
        case BOOK3S_INTERRUPT_MACHINE_CHECK:
+       {
+               static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL,
+                                             DEFAULT_RATELIMIT_BURST);
                /* Pass the machine check to the L1 guest */
                r = RESUME_HOST;
                /* Print the MCE event to host console. */
-               if (printk_ratelimit())
+               if (__ratelimit(&rs))
                        machine_check_print_event_info(&vcpu->arch.mce_evt, 
false, true);
                break;
+       }
        /*
         * We get these next two if the guest accesses a page which it thinks
         * it has mapped but which is not actually present, either because


cheers