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From:   Jue Wang <juew@google.com>
Date:   Thu, 22 Jul 2021 06:54:37 -0700
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Subject: Re: [PATCH 2/3] x86/mce: Avoid infinite loop for copy from user recovery
To:     "Luck, Tony" <tony.luck@intel.com>
Cc:     Borislav Petkov <bp@alien8.de>, dinghui@sangfor.com.cn,
        huangcun@sangfor.com.cn, linux-edac@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= 
        <naoya.horiguchi@nec.com>, Oscar Salvador <osalvador@suse.de>,
        x86 <x86@kernel.org>, "Song, Youquan" <youquan.song@intel.com>
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This patch assumes the UC error consumed in kernel is always the same UC.

Yet it's possible two UCs on different pages are consumed in a row.
The patch below will panic on the 2nd MCE. How can we make the code works
on multiple UC errors?


> + int count = ++current->mce_count;
> +
> + /* First call, save all the details */
> + if (count == 1) {
> + current->mce_addr = m->addr;
> + current->mce_kflags = m->kflags;
> + current->mce_ripv = !!(m->mcgstatus & MCG_STATUS_RIPV);
> + current->mce_whole_page = whole_page(m);
> + current->mce_kill_me.func = func;
> + }
> ......
> + /* Second or later call, make sure page address matches the one from first call */
> + if (count > 1 && (current->mce_addr >> PAGE_SHIFT) != (m->addr >> PAGE_SHIFT))
> + mce_panic("Machine checks to different user pages", m, msg);