Hello,
On Wed, Jul 01, 2020 at 12:52:29PM +0530, Aneesh Kumar K.V wrote:
> The PAPR based virtualized persistent memory devices are only supported on
> POWER9 and above. In the followup patch, the kernel will switch the persistent
> memory cache flush functions to use a new `dcbf` variant instruction. The new
> instructions even though added in ISA 3.1 works even on P8 and P9 because
> these
> are implemented as a variant of existing `dcbf` and `hwsync` and on P8 and
> P9 behaves as such.
>
> Considering these devices are only supported on P8 and above, update the
> driver
> to prevent a P7-compat guest from using persistent memory devices.
>
> We don't update of_pmem driver with the same condition, because, on
> bare-metal,
> the firmware enables pmem support only on P9 and above. There the kernel
> depends
> on OPAL firmware to restrict exposing persistent memory related device tree
> entries on older hardware. of_pmem.ko is written without any arch dependency
> and
> we don't want to add ppc64 specific cpu feature check in of_pmem driver.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
> ---
> arch/powerpc/platforms/pseries/pmem.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/arch/powerpc/platforms/pseries/pmem.c
> b/arch/powerpc/platforms/pseries/pmem.c
> index f860a897a9e0..2347e1038f58 100644
> --- a/arch/powerpc/platforms/pseries/pmem.c
> +++ b/arch/powerpc/platforms/pseries/pmem.c
> @@ -147,6 +147,12 @@ const struct of_device_id drc_pmem_match[] = {
>
> static int pseries_pmem_init(void)
> {
> + /*
> + * Only supported on POWER8 and above.
> + */
> + if (!cpu_has_feature(CPU_FTR_ARCH_207S))
> + return 0;
> +
This looks superfluous.
The hypervisor is responsible for publishing the pmem in devicetree when
present, kernel is responsible for using it when supported by the
kernel.
Or is there a problem that the flush instruction is not available in P7
compat mode?
Even then volatile regions should still work.
Thanks
Michal
