On Thu, 17 Dec 2020, Bertrand Marquis wrote:
> Create a cpuinfo structure for guest and mask into it the features that
> we do not support in Xen or that we do not want to publish to guests.
>
> Modify some values in the cpuinfo structure for guests to mask some
> features which we do not want to allow to guests (like AMU) or we do not
> support (like SVE).
> Modify some values in the guest cpuinfo structure to guests to hide some
> processor features:
> - SVE as this is not supported by Xen and guest are not allowed to use
> this features (ZEN is set to 0 in CPTR_EL2).
> - AMU as HCPTR_TAM is set in CPTR_EL2 so AMU cannot be used by guests
> All other bits are left untouched.
> - RAS as this is not supported by Xen.
>
> The code is trying to group together registers modifications for the
> same feature to be able in the long term to easily enable/disable a
> feature depending on user parameters or add other registers modification
> in the same place (like enabling/disabling HCR bits).
>
> Signed-off-by: Bertrand Marquis <bertrand.marq...@arm.com>
Reviewed-by: Stefano Stabellini <sstabell...@kernel.org>
> ---
> Changes in V2: Rebase
> Changes in V3:
> Use current_cpu_data info instead of recalling identify_cpu
> Changes in V4:
> Use boot_cpu_data instead of current_cpu_data
> Use "hide XX support" instead of disable as this part of the code is
> actually only hidding feature to guests but not disabling them (this
> is done through the HCR register).
> Modify commit message to be more clear about what is done in
> guest_cpuinfo.
>
> ---
> xen/arch/arm/cpufeature.c | 51 ++++++++++++++++++++++++++++++++
> xen/include/asm-arm/cpufeature.h | 2 ++
> 2 files changed, 53 insertions(+)
>
> diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
> index 86b99ee960..1f6a85aafe 100644
> --- a/xen/arch/arm/cpufeature.c
> +++ b/xen/arch/arm/cpufeature.c
> @@ -24,6 +24,8 @@
>
> DECLARE_BITMAP(cpu_hwcaps, ARM_NCAPS);
>
> +struct cpuinfo_arm __read_mostly guest_cpuinfo;
> +
> void update_cpu_capabilities(const struct arm_cpu_capabilities *caps,
> const char *info)
> {
> @@ -151,6 +153,55 @@ void identify_cpu(struct cpuinfo_arm *c)
> c->mvfr.bits[2] = READ_SYSREG(MVFR2_EL1);
> }
>
> +/*
> + * This function is creating a cpuinfo structure with values modified to mask
> + * all cpu features that should not be published to guest.
> + * The created structure is then used to provide ID registers values to
> guests.
> + */
> +static int __init create_guest_cpuinfo(void)
> +{
> + /*
> + * TODO: The code is currently using only the features detected on the
> boot
> + * core. In the long term we should try to compute values containing only
> + * features supported by all cores.
> + */
> + guest_cpuinfo = boot_cpu_data;
> +
> +#ifdef CONFIG_ARM_64
> + /* Hide MPAM support as xen does not support it */
> + guest_cpuinfo.pfr64.mpam = 0;
> + guest_cpuinfo.pfr64.mpam_frac = 0;
> +
> + /* Hide SVE as Xen does not support it */
> + guest_cpuinfo.pfr64.sve = 0;
> + guest_cpuinfo.zfr64.bits[0] = 0;
> +
> + /* Hide MTE support as Xen does not support it */
> + guest_cpuinfo.pfr64.mte = 0;
> +#endif
> +
> + /* Hide AMU support */
> +#ifdef CONFIG_ARM_64
> + guest_cpuinfo.pfr64.amu = 0;
> +#endif
> + guest_cpuinfo.pfr32.amu = 0;
> +
> + /* Hide RAS support as Xen does not support it */
> +#ifdef CONFIG_ARM_64
> + guest_cpuinfo.pfr64.ras = 0;
> + guest_cpuinfo.pfr64.ras_frac = 0;
> +#endif
> + guest_cpuinfo.pfr32.ras = 0;
> + guest_cpuinfo.pfr32.ras_frac = 0;
> +
> + return 0;
> +}
> +/*
> + * This function needs to be run after all smp are started to have
> + * cpuinfo structures for all cores.
> + */
> +__initcall(create_guest_cpuinfo);
> +
> /*
> * Local variables:
> * mode: C
> diff --git a/xen/include/asm-arm/cpufeature.h
> b/xen/include/asm-arm/cpufeature.h
> index 74139be1cc..6058744c18 100644
> --- a/xen/include/asm-arm/cpufeature.h
> +++ b/xen/include/asm-arm/cpufeature.h
> @@ -283,6 +283,8 @@ extern void identify_cpu(struct cpuinfo_arm *);
> extern struct cpuinfo_arm cpu_data[];
> #define current_cpu_data cpu_data[smp_processor_id()]
>
> +extern struct cpuinfo_arm guest_cpuinfo;
> +
> #endif /* __ASSEMBLY__ */
>
> #endif
> --
> 2.17.1
>
