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

[Eduardo Habkost]

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?


> 
> Add a cmdline option "tsx=fake" to not clear CPUID bits even when the
> hardware always aborts TSX transactions.
> 
> Suggested-by: Tony Luck <tony.luck@xxxxxxxxx>
> Suggested-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
> Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
> Tested-by: Neelima Krishnan <neelima.krishnan@xxxxxxxxx>
[...]

-- 
Eduardo