lkml.org 
[lkml]   [2020]   [Feb]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 48/61] KVM: x86: Do host CPUID at load time to mask KVM cpu caps
On Tue, Feb 25, 2020 at 01:08:43PM -0800, Sean Christopherson wrote:
> On Tue, Feb 25, 2020 at 04:18:12PM +0100, Paolo Bonzini wrote:
> > On 01/02/20 19:52, Sean Christopherson wrote:
> > > +#ifdef CONFIG_KVM_CPUID_AUDIT
> > > + /* Entry needs to be fully populated when auditing is enabled. */
> > > + entry.function = cpuid.function;
> > > + entry.index = cpuid.index;
> > > +#endif
> >
> > This shows that the audit case is prone to bitrot, which is good reason
> > to enable it by default.
>
> I have no argument against that, especially since I missed this case during
> development and only caught it when running on a different system that I
> had happened to configure with CONFIG_KVM_CPUID_AUDIT=y. :-)

I ended up dropping the audit code altogether. The uops overhead wasn't
bad, but the code bloat was pretty rough, ~16 bytes per instance. The
final nail in the coffin was that the auditing would trigger false
positives if userspace configured CPUID leafs with a non-signficant index
to have a non-zero index, e.g. is_matching_cpuid_entry() ignores the index
if KVM_CPUID_FLAG_SIGNIFCANT_INDEX isn't set.

\
 
 \ /
  Last update: 2020-02-29 19:39    [W:0.117 / U:2.908 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site