Re: [PATCH v2 6/6] x86: vmx: virtualize split lock detection

[Andy Lutomirski]

On Mon, Feb 3, 2020 at 7:21 AM Xiaoyao Li <xiaoyao.li@xxxxxxxxx> wrote:
>
> Due to the fact that MSR_TEST_CTRL is per-core scope, i.e., the sibling
> threads in the same physical CPU core share the same MSR, only
> advertising feature split lock detection to guest when SMT is disabled
> or unsupported for simplicitly.
>
> Only when host is sld_off, can guest control the hardware value of
> MSR_TEST_CTL, i.e., KVM loads guest's value into hardware when vcpu is
> running.
>
> The vmx->disable_split_lock_detect can be set to true after unhandled
> split_lock #AC in guest only when host is sld_warn mode. It's for not
> burnning old guest, of course malicous guest can exploit it for DoS
> attack.

Is this actually worthwhile?  This only applies to the host having
sld=off or warn and the host having HT off.  I suspect that
deployments supporting migration will not want to use this, and
multi-tenant deployments won't want to use it for SLD-aware guests doe
to DoS risk.

--Andy