Re: [Qemu-devel] [PATCH 1/3] target-i386: kvm: Abort if MCE bank count is not supported by host

[Paolo Bonzini]

On 25/11/2015 16:49, Eduardo Habkost wrote:
> Instead of silently changing the number of banks in mcg_cap based
> on kvm_get_mce_cap_supported(), abort initialization if the host
> doesn't support MCE_BANKS_DEF banks.
> 
> Note that MCE_BANKS_DEF was always 10 since it was introduced in
> QEMU, and Linux always returned 32 at KVM_CAP_MCE since
> KVM_CAP_MCE was introduced, so no behavior is being changed and
> the error can't be triggered by any Linux version. The point of
> the new check is to ensure we won't silently change the bank
> count if we change MCE_BANKS_DEF or make the bank count
> configurable in the future.
> 
> Signed-off-by: Eduardo Habkost <address@hidden>
> ---
>  target-i386/kvm.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index 2a9953b..ee7bc69 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -784,11 +784,14 @@ int kvm_arch_init_vcpu(CPUState *cs)
>              return ret;
>          }
>  
> -        if (banks > MCE_BANKS_DEF) {
> -            banks = MCE_BANKS_DEF;
> +        if (MCE_BANKS_DEF > banks) {
> +            error_report("kvm: Unsupported MCE bank count: %d > %d\n",
> +                         MCE_BANKS_DEF, banks);

Yoda conditions?

        if (banks < MCE_BANKS_DEF) {
            error_report("kvm: Unsupported MCE bank count (QEMU = %d, KVM = 
%d)",
                         MCE_BANKS_DEF, banks);

Paolo

> +            return -ENOTSUP;
>          }
> +
>          mcg_cap &= MCE_CAP_DEF;
> -        mcg_cap |= banks;
> +        mcg_cap |= MCE_BANKS_DEF;
>          ret = kvm_vcpu_ioctl(cs, KVM_X86_SETUP_MCE, &mcg_cap);
>          if (ret < 0) {
>              fprintf(stderr, "KVM_X86_SETUP_MCE: %s", strerror(-ret));
>