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From:   "Luck, Tony" <tony.luck@intel.com>
To:     Peter Zijlstra <peterz@infradead.org>
CC:     Borislav Petkov <bp@alien8.de>, "x86@kernel.org" <x86@kernel.org>,
        "Andrew Morton" <akpm@linux-foundation.org>,
        Darren Hart <dvhart@infradead.org>,
        Andy Lutomirski <luto@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-edac@vger.kernel.org" <linux-edac@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: RE: [PATCH 2/2] futex, x86/mce: Avoid double machine checks
Thread-Topic: [PATCH 2/2] futex, x86/mce: Avoid double machine checks
Thread-Index: AQHW5gzS994+pBz0+EqmRhsWwoX/Iaoe2m6A//9/AZA=
Date:   Fri, 8 Jan 2021 23:08:58 +0000
Message-ID: <4493a015ffcd4d82bbea7d1e5c2e73e4@intel.com>
References: <20210108222251.14391-1-tony.luck@intel.com>
 <20210108222251.14391-3-tony.luck@intel.com>
 <20210108224715.GB2453@worktop.programming.kicks-ass.net>
In-Reply-To: <20210108224715.GB2453@worktop.programming.kicks-ass.net>
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Precedence: bulk

> I think this is horrid; why can't we have it return something different
> then -EFAULT instead?

I did consider this ... but it appears that architectures aren't unified in the
return value from get_user()

Here's another function involved in the futex call chain leading to this:

static int get_futex_value_locked(u32 *dest, u32 __user *from)
{
        int ret;

        pagefault_disable();
        ret = __get_user(*dest, from);
        pagefault_enable();

        return ret ? -EFAULT : 0;
}

It seems like the expectation here is just "zero or not" and we
don't care what the "not" value is ... just turn it into -EFAULT.

-Tony