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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Thu, 22 Sep 2022 23:59:13 +0300
Message-ID: <CAHp75VeVKUxnERF0bA_ivBuvb9JsME3b4MgX=TxHhtvghF1w6A@mail.gmail.com>
Subject: Re: [PATCH v2] x86/platform/uv: Dont use smp_processor_id while preemptible
To:     Mike Travis <mike.travis@hpe.com>
Cc:     Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Steve Wahl <steve.wahl@hpe.com>, x86@kernel.org,
        Dimitri Sivanich <dimitri.sivanich@hpe.com>,
        stable@vger.kernel.org, Andy Shevchenko <andy@infradead.org>,
        Darren Hart <dvhart@infradead.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Russ Anderson <russ.anderson@hpe.com>,
        linux-kernel@vger.kernel.org, platform-driver-x86@vger.kernel.org
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On Thu, Sep 22, 2022 at 11:01 PM Mike Travis <mike.travis@hpe.com> wrote:
>
> To avoid a "BUG: using smp_processor_id() in preemptible" debug warning
> message, disable preemption around use of the processor id.  This code
> sequence merely decides which portal that this CPU uses to read the RTC.
> It does this to avoid thrashing the cache but even if preempted it still
> reads the same time from the single RTC clock.

...

> Signed-off-by: Mike Travis <mike.travis@hpe.com>
> Reviewed-by: Steve Wahl <steve.wahl@hpe.com>
> Reviewed-by: Dimitri Sivanich <dimitri.sivanich@hpe.com>
> Cc: stable@vger.kernel.org

No kernel version? No Fixes tag?

...

> -               offset = (uv_blade_processor_id() * L1_CACHE_BYTES) % PAGE_SIZE;
> +               offset = (uv_cpu_blade_processor_id(cpu) * L1_CACHE_BYTES) % PAGE_SIZE;

Perhaps it can be transformed to use offset_in_page() at the same time.

-- 
With Best Regards,
Andy Shevchenko