Re: [PATCH] arm64: Add KRYO{3,4}XX CPU cores to spectre-v2 safe list

[Doug Anderson]

Hi,

On Thu, Jan 16, 2020 at 8:11 AM Sai Prakash Ranjan
<saiprakash.ranjan@xxxxxxxxxxxxxx> wrote:
>
> Hi Will,
>
> On 2020-01-16 21:02, Will Deacon wrote:
> > [+Jeffrey]
> >
> > On Thu, Jan 16, 2020 at 07:49:12PM +0530, Sai Prakash Ranjan wrote:
> >> KRYO3XX silver CPU cores and KRYO4XX silver, gold CPU cores
> >> are not affected by Spectre variant 2. Add them to spectre_v2
> >> safe list to correct ARM_SMCCC_ARCH_WORKAROUND_1 warning and
> >> vulnerability sysfs value.
> >>
> >> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> >> ---
> >>  arch/arm64/include/asm/cputype.h | 6 ++++++
> >>  arch/arm64/kernel/cpu_errata.c   | 3 +++
> >>  2 files changed, 9 insertions(+)
> >>
> >> diff --git a/arch/arm64/include/asm/cputype.h
> >> b/arch/arm64/include/asm/cputype.h
> >> index aca07c2f6e6e..7219cddeba66 100644
> >> --- a/arch/arm64/include/asm/cputype.h
> >> +++ b/arch/arm64/include/asm/cputype.h
> >> @@ -85,6 +85,9 @@
> >>  #define QCOM_CPU_PART_FALKOR_V1             0x800
> >>  #define QCOM_CPU_PART_FALKOR                0xC00
> >>  #define QCOM_CPU_PART_KRYO          0x200
> >> +#define QCOM_CPU_PART_KRYO_3XX_SILVER       0x803
> >> +#define QCOM_CPU_PART_KRYO_4XX_GOLD 0x804
> >> +#define QCOM_CPU_PART_KRYO_4XX_SILVER       0x805
> >
> > Jeffrey is the only person I know who understands the CPU naming here,
> > so
> > I've added him in case this needs either renaming or extending to cover
> > other CPUs. I wouldn't be at all surprised if we need a function call
> > rather than a bunch of table entries...
> >
> > That said, the internet claims that KRYO4XX gold is based on
> > Cortex-A76,
> > and so CSV2 should be set...
> >
>
> Yes the internet claims are true and CSV2 is set. SANITY check logs in
> here show ID_PFR0_EL1 - https://lore.kernel.org/patchwork/patch/1138457/

I'm probably just being a noob here and am confused, but if CSV2 is
set then why do you need your patch at all?  The code I see says that
if CSV2 is set then we don't even check the spectre_v2_safe_list().

-Doug