Re: [Xen-devel] [PATCH v2 2/6] xen/arm: Provide macros to help creating workaround helpers

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 27 Jul 2016, Julien Grall wrote:
> Workarounds may require to execute a different path when the platform
> is affected by the associated erratum. Furthermore, this may need to
> be called in the common code.
> 
> To avoid too much intrusion/overhead, the workaround helpers need to
> be a nop on architecture which will never have the workaround and have
> to be quick to check whether the platform requires it.
> 
> The alternative framework is used to transform the check in a single
> instruction. When the framework is not available, the helper will have
> ~6 instructions including 1 instruction load.
> 
> The macro will create a handler called check_workaround_xxxxx with
> xxxx the erratum number.
> 
> For instance, the line bellow will create a workaround helper for
> erratum #424242 which is enabled when the capability
> ARM64_WORKAROUND_424242 is set and only available for ARM64:
> 
> CHECK_WORKAROUND_HELPER(424242, ARM64_WORKAROUND_42424242, CONFIG_ARM64)
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>     Changes in v2:
>         - Add Konrad's reviewed-by
> ---
>  xen/include/asm-arm/cpuerrata.h | 39 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/xen/include/asm-arm/cpuerrata.h b/xen/include/asm-arm/cpuerrata.h
> index c495ee5..2982a92 100644
> --- a/xen/include/asm-arm/cpuerrata.h
> +++ b/xen/include/asm-arm/cpuerrata.h
> @@ -1,8 +1,47 @@
>  #ifndef __ARM_CPUERRATA_H__
>  #define __ARM_CPUERRATA_H__
>  
> +#include <xen/config.h>
> +#include <asm/cpufeature.h>
> +#include <asm/alternative.h>
> +
>  void check_local_cpu_errata(void);
>  
> +#ifdef CONFIG_ALTERNATIVE
> +
> +#define CHECK_WORKAROUND_HELPER(erratum, feature, arch)         \
> +static inline bool_t check_workaround_##erratum(void)           \
> +{                                                               \
> +    if ( !IS_ENABLED(arch) )                                    \
> +        return 0;                                               \
> +    else                                                        \
> +    {                                                           \
> +        bool_t ret;                                             \
> +                                                                \
> +        asm volatile (ALTERNATIVE("mov %0, #0",                 \
> +                                  "mov %0, #1",                 \
> +                                  feature)                      \
> +                      : "=r" (ret));                            \
> +                                                                \
> +        return unlikely(ret);                                   \
> +    }                                                           \
> +}
> +
> +#else /* CONFIG_ALTERNATIVE */
> +
> +#define CHECK_WORKAROUND_HELPER(erratum, feature, arch)         \
> +static inline bool_t check_workaround_##erratum(void)           \
> +{                                                               \
> +    if ( !IS_ENABLED(arch) )                                    \
> +        return 0;                                               \
> +    else                                                        \
> +        return unlikely(cpus_have_cap(feature));                \
> +}
> +
> +#endif
> +
> +#undef CHECK_WORKAROUND_HELPER
> +
>  #endif /* __ARM_CPUERRATA_H__ */
>  /*
>   * Local variables:
> -- 
> 1.9.1
> 

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