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SubjectRe: [PATCH v5 02/27] arm64: cpufeature: Use alternatives for VHE cpu_enable
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Hi Julien,

On 28/08/18 16:51, Julien Thierry wrote:
> The cpu_enable callback for VHE feature requires all alternatives to have
> been applied. This prevents applying VHE alternative separately from the
> rest.
>
> Use an alternative depending on VHE feature to know whether VHE
> alternatives have already been applied.

> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 1e433ac..3bc1c8b 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1022,8 +1024,15 @@ static void cpu_copy_el2regs(const struct arm64_cpu_capabilities *__unused)
> * that, freshly-onlined CPUs will set tpidr_el2, so we don't need to
> * do anything here.
> */
> - if (!alternatives_applied)
> - write_sysreg(read_sysreg(tpidr_el1), tpidr_el2);
> + asm volatile(ALTERNATIVE(
> + "mrs %0, tpidr_el1\n"
> + "msr tpidr_el2, %0",
> + "nop\n"
> + "nop",
> + ARM64_HAS_VIRT_HOST_EXTN)
> + : "+r" (tmp)
> + :
> + : "memory");
> }
> #endif

Catalin's preference was to keep this all in C:
https://patchwork.kernel.org/patch/10007977/
, for which we need to know if 'the' alternative has been applied.

I suspect there may be more registers in this list if we have to switch to
another EL2 register using alternatives. (but I don't have an example).

Could we make 'alternatives_applied' a macro that takes the cap as an argument?


Thanks,

James

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