On Mon, 5 Oct 2020 18:51:44 +0200
Cédric Le Goater <c...@kaod.org> wrote:
> StoreEOI on POWER9 CPUs is racy because load-after-store ordering is
> not enforced.
>
> Signed-off-by: Cédric Le Goater <c...@kaod.org>
> ---
> hw/ppc/spapr_caps.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
> index b0a9d0227db2..9251badbdc27 100644
> --- a/hw/ppc/spapr_caps.c
> +++ b/hw/ppc/spapr_caps.c
> @@ -549,6 +549,15 @@ static void cap_storeeoi_apply(SpaprMachineState *spapr,
> uint8_t val,
> error_setg(errp, "StoreEOI not supported by KVM");
> return;
> }
> +
> + /*
> + * load-after-store ordering is not enforced on POWER9 CPUs
> + * and StoreEOI can be racy.
> + */
> + if (!ppc_type_check_compat(machine->cpu_type,
> CPU_POWERPC_LOGICAL_3_10,
> + 0, spapr->max_compat_pvr)) {
> + warn_report("StoreEOI on a POWER9 CPU is unsafe on KVM.");
It all boils down to what "unsafe" really means here... if the outcome is
"very likely hang the guest" as soon as it starts doing I/O, shouldn't
we error out instead ? What is the motivation to use StoreEOI if the
processor doesn't really support it ?
> + }
> }
> }
>
