From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eduardo Habkost <ehabkost@redhat.com>
Subject: Re: [PATCH 1/3] target-i386: kvm: Abort if MCE bank
 count is not supported by host
Date: Wed, 25 Nov 2015 15:26:17 -0200
Message-ID: <20151125172617.GS23717@thinpad.lan.raisama.net>
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Cc: kvm@vger.kernel.org, Marcelo Tosatti <mtosatti@redhat.com>,
	qemu-devel@nongnu.org, Borislav Petkov <bp@alien8.de>,
	ying.huang@intel.com, Andreas =?iso-8859-1?Q?F=E4rber?= <afaerber@suse.de>,
	Richard Henderson <rth@twiddle.net>
To: Paolo Bonzini <pbonzini@redhat.com>
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On Wed, Nov 25, 2015 at 05:46:38PM +0100, Paolo Bonzini wrote:
> 
> 
> 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 <ehabkost@redhat.com>
> > ---
> >  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);

This was on purpose, because MCE_BANKS_DEF is replaced by
(env->mcg_caps & MCG_CAPS_COUNT_MASK) in the next patch.

-- 
Eduardo