Re: [PATCH 4/4] powerpc/powernv: Remove POWER9 PVR version check for entry and uaccess flushes

On Tue, 4 May 2021 at 09:16, Nicholas Piggin [off-list ref] wrote:

Excerpts from Joel Stanley's message of May 4, 2021 10:51 am:

quoted

On Mon, 3 May 2021 at 13:04, Nicholas Piggin [off-list ref] wrote:

quoted

These aren't necessarily POWER9 only, and it's not to say some new
vulnerability may not get discovered on other processors for which
we would like the flexibility of having the workaround enabled by
firmware.

Remove the restriction that they only apply to POWER9.

I was wondering how these worked which led me to reviewing your patch.
From what I could see, these are enabled by default (SEC_FTR_DEFAULT
in arch/powerpc/include/asm/security_features.h), so unless all
non-POWER9 machines have set the "please don't" bit in their firmware
this patch will enable the feature for those machines. Is that what
you wanted?

Yes. POWER7/8 should be affected (it's similar mechanism that requires
the meltdown RFI flush, which those processors need).

POWER10 we haven't released a bare metal firmware with the right bits
yet. Not urgent at the moment but wouldn't hurt to specify them and
add the Linux code for them.

Thanks for the explanation. This could go in the commit message if you re-spin.

Reviewed-by: Joel Stanley <joel@jms.id.au>