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SubjectRe: [PATCH 2/7] x86, xsave: introduce xstate enable functions
On 21.07.10 17:53:31, H. Peter Anvin wrote:

> From 55b936c7a359a14d72bcba6c3fceba4cfbe3fedf Mon Sep 17 00:00:00 2001
> From: H. Peter Anvin <hpa@linux.intel.com>
> Date: Wed, 21 Jul 2010 14:23:10 -0700
> Subject: [PATCH] x86, xsave: Make xstate_enable_boot_cpu() __init, protect on CPU 0
>
> xstate_enable_boot_cpu() is, as the name implies, only used on the
> boot CPU; furthermore, it invokes alloc_bootmem(), which is __init;
> hence it needs to be tagged __init rather than __cpuinit.
>
> Furthermore, it is *not* safe in the long run to rely on CPU 0 only
> coming online during the early boot -- at some point we're going to
> support offlining (and re-onlining) the boot CPU, and at that point we
> must not call xstate_enable_boot_cpu() again.
>
> The code is a fair bit more obscure than one would like, because the
> __ref overrides aren't quite powerful enough.
>
> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
> Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>
> Cc: Robert Richter <robert.richter@amd.com>
> LKML-Reference: <4C476236.1020302@zytor.com>

I am fine with your changes.

> void __cpuinit xsave_init(void)
> {
> + static __refdata void (*next_func)(void) = xstate_enable_boot_cpu;
> + void (*this_func)(void);
> +
> if (!cpu_has_xsave)
> return;
>
> - /*
> - * Boot processor to setup the FP and extended state context info.
> - */
> - if (!smp_processor_id())
> - xstate_enable_boot_cpu();
> - else
> - xstate_enable(pcntxt_mask);
> + this_func = next_func;
> + next_func = xstate_enable;
> + this_func();
> }

Just wondering why you are using this_func()? Instead, you could
simply do:

next_func();
next_func = xstate_enable;

Do you see races when bringing up multiple cpus in parallel?

Thanks.

-Robert

--
Advanced Micro Devices, Inc.
Operating System Research Center



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