Re: [PATCH 4/4] x86/tsx: Add cmdline tsx=fake to not clear CPUID bits RTM and HLE

[Pawan Gupta]

On 06.07.2021 17:19, Eduardo Habkost wrote:
> On Tue, Jul 6, 2021 at 5:15 PM Pawan Gupta
> <pawan.kumar.gupta@xxxxxxxxxxxxxxx> wrote:
> > On 06.07.2021 15:52, Eduardo Habkost wrote:
> > >On Wed, Jun 09, 2021 at 02:14:39PM -0700, Pawan Gupta wrote:
> > >> On CPUs that deprecated TSX, clearing the enumeration bits CPUID.RTM and
> > >> CPUID.HLE may not be desirable in some corner cases. Like a saved guest
> > >> would refuse to resume if it was saved before the microcode update
> > >> that deprecated TSX.
> > >
> > >Why is a global option necessary to allow those guests to be
> > >resumed?  Why can't KVM_GET_SUPPORTED_CPUID always return the HLE
> > >and RTM bits as supported when the host CPU has them?
> >
> > Yes, the global option is unnecessary and this patch was dropped in v2.
>
> Was the behaviour this patch originally tried to fix changed in v2 as
> well? Is it going to be possible to resume a HLE=1,RTM=1 VM on a
> TSX_FORCE_ABORT=1 host with no extra kernel command line options
> needed?

The problem it tried to solve is still present, but the global switch
was thought to be unnecessary. I see that Paolo has some suggestions to
fix this in the userspace.

Thanks,
Pawan