Re: [Xen-devel] [PATCH 1/5] xen/arm: Introduce enable callback to enable a capabilities on each online CPU

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 16 Jan 2018, Julien Grall wrote:
> Once Xen knows what features/workarounds present on the platform, it
> might be necessary to configure each online CPU.
> 
> Introduce a new callback "enable" that will be called on each online CPU to
> configure the "capability".
> 
> The code is based on Linux v4.14 (where cpufeature.c comes from), the
> explanation of why using stop_machine_run is kept as we have similar
> problem in the future.
> 
> Lastly introduce enable_errata_workaround that will be called once CPUs
> have booted and before the hardware domain is created.
> 
> This is part of XSA-254.
> 
> Signed-of-by: Julien Grall <julien.grall@xxxxxxxxxx>

If you took the code from Linux, you need to add the original
Signed-off-by from the Linux commit. Aside from that:

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>  xen/arch/arm/cpuerrata.c         |  6 ++++++
>  xen/arch/arm/cpufeature.c        | 29 +++++++++++++++++++++++++++++
>  xen/arch/arm/setup.c             |  1 +
>  xen/include/asm-arm/cpuerrata.h  |  1 +
>  xen/include/asm-arm/cpufeature.h |  3 +++
>  5 files changed, 40 insertions(+)
> 
> diff --git a/xen/arch/arm/cpuerrata.c b/xen/arch/arm/cpuerrata.c
> index fe9e9facbe..772587c05a 100644
> --- a/xen/arch/arm/cpuerrata.c
> +++ b/xen/arch/arm/cpuerrata.c
> @@ -64,6 +64,12 @@ void check_local_cpu_errata(void)
>  {
>      update_cpu_capabilities(arm_errata, "enabled workaround for");
>  }
> +
> +void __init enable_errata_workarounds(void)
> +{
> +    enable_cpu_capabilities(arm_errata);
> +}
> +
>  /*
>   * Local variables:
>   * mode: C
> diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
> index 479c9fb011..525b45e22f 100644
> --- a/xen/arch/arm/cpufeature.c
> +++ b/xen/arch/arm/cpufeature.c
> @@ -19,6 +19,7 @@
>  #include <xen/types.h>
>  #include <xen/init.h>
>  #include <xen/smp.h>
> +#include <xen/stop_machine.h>
>  #include <asm/cpufeature.h>
>  
>  DECLARE_BITMAP(cpu_hwcaps, ARM_NCAPS);
> @@ -40,6 +41,34 @@ void update_cpu_capabilities(const struct 
> arm_cpu_capabilities *caps,
>  }
>  
>  /*
> + * Run through the enabled capabilities and enable() it on all active
> + * CPUs.
> + */
> +void __init enable_cpu_capabilities(const struct arm_cpu_capabilities *caps)
> +{
> +    for ( ; caps->matches; caps++ )
> +    {
> +        if ( !cpus_have_cap(caps->capability) )
> +            continue;
> +
> +        if ( caps->enable )
> +        {
> +            int ret;
> +
> +            /*
> +             * Use stop_machine_run() as it schedules the work allowing
> +             * us to modify PSTATE, instead of on_each_cpu() which uses
> +             * an IPI, giving us a PSTATE that disappears when we
> +             * return.
> +             */
> +            ret = stop_machine_run(caps->enable, (void *)caps, NR_CPUS);
> +            /* stop_machine_run should never fail at this stage of the boot. 
> */
> +            BUG_ON(ret);
> +        }
> +    }
> +}
> +
> +/*
>   * Local variables:
>   * mode: C
>   * c-file-style: "BSD"
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index 16a3b1be8e..032a6a882d 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -849,6 +849,7 @@ void __init start_xen(unsigned long boot_phys_offset,
>       * stop_machine (tasklets initialized via an initcall).
>       */
>      apply_alternatives_all();
> +    enable_errata_workarounds();
>  
>      /* Create initial domain 0. */
>      /* The vGIC for DOM0 is exactly emulating the hardware GIC */
> diff --git a/xen/include/asm-arm/cpuerrata.h b/xen/include/asm-arm/cpuerrata.h
> index 8b158429c7..7de68361ff 100644
> --- a/xen/include/asm-arm/cpuerrata.h
> +++ b/xen/include/asm-arm/cpuerrata.h
> @@ -5,6 +5,7 @@
>  #include <asm/alternative.h>
>  
>  void check_local_cpu_errata(void);
> +void enable_errata_workarounds(void);
>  
>  #ifdef CONFIG_HAS_ALTERNATIVE
>  
> diff --git a/xen/include/asm-arm/cpufeature.h 
> b/xen/include/asm-arm/cpufeature.h
> index f00b6dbd39..21c65e198c 100644
> --- a/xen/include/asm-arm/cpufeature.h
> +++ b/xen/include/asm-arm/cpufeature.h
> @@ -74,6 +74,7 @@ struct arm_cpu_capabilities {
>      const char *desc;
>      u16 capability;
>      bool (*matches)(const struct arm_cpu_capabilities *);
> +    int (*enable)(void *); /* Called on every active CPUs */
>      union {
>          struct {    /* To be used for eratum handling only */
>              u32 midr_model;
> @@ -85,6 +86,8 @@ struct arm_cpu_capabilities {
>  void update_cpu_capabilities(const struct arm_cpu_capabilities *caps,
>                               const char *info);
>  
> +void enable_cpu_capabilities(const struct arm_cpu_capabilities *caps);
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif
> -- 
> 2.11.0
> 

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