Re: [Xen-devel] [PATCH 5/5] xen/arm64: Implement branch predictor hardening for affected Cortex-A CPUs

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Stefano,

On 17/01/18 00:42, Stefano Stabellini wrote:
> On Tue, 16 Jan 2018, Julien Grall wrote:
> >   #define MIDR_RANGE(model, min, max)     \
> > @@ -205,6 +232,28 @@ static const struct arm_cpu_capabilities arm_errata[] = {
> >                      (1 << MIDR_VARIANT_SHIFT) | 2),
> >       },
> >   #endif
> > +#ifdef CONFIG_ARM64_HARDEN_BRANCH_PREDICTOR
> > +    {
> > +        .capability = ARM_HARDEN_BRANCH_PREDICTOR,
> > +        MIDR_ALL_VERSIONS(MIDR_CORTEX_A57),
> > +        .enable = enable_psci_bp_hardening,
> > +    },
> > +    {
> > +        .capability = ARM_HARDEN_BRANCH_PREDICTOR,
> > +        MIDR_ALL_VERSIONS(MIDR_CORTEX_A72),
> > +        .enable = enable_psci_bp_hardening,
> > +    },
> > +    {
> > +        .capability = ARM_HARDEN_BRANCH_PREDICTOR,
> > +        MIDR_ALL_VERSIONS(MIDR_CORTEX_A73),
> > +        .enable = enable_psci_bp_hardening,
> > +    },
> > +    {
> > +        .capability = ARM_HARDEN_BRANCH_PREDICTOR,
> > +        MIDR_ALL_VERSIONS(MIDR_CORTEX_A75),
> > +        .enable = enable_psci_bp_hardening,
> > +    },
> We need to add a basic description in the desc field as it is printed by
> update_cpu_capabilities.
desc field is not mandatory, and in that case I think the print would be 
confusing. At the difference of the other errata, we have more check in 
install_bp_hardening_vec that may result to skip the hardening.
The errata here is covering all variant/revision of A75 models for 
safety reason. Arm has introduced a new field ID_AA64PFR0_EL1.CSV2 to 
tell whether a branch predictor trained in one context will affect 
speculative execution in another context. This field is checked in 
install_bp_hardening_vec so you avoid to harden the vector tables and 
small performance hit.
IHMO, it would be better to have a per-CPU message in 
install_bp_hardening_vec announcing whether the vector tables has been 
harden and the kind of hardening.
What do you think?

Cheers,

> > +#endif
> >       {},
> >   };
> >   
> > --
> > 2.11.0
--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel