linux-kernel - Re: [PATCH 2/3] x86/mce: Avoid infinite loop for copy from user recovery

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Message-ID: <CAPcxDJ7YsnYtyzSmgfBj-rmALkjigKx2ODB=SCYCzY8FJYg4iA@mail.gmail.com>
Date:   Thu, 22 Jul 2021 06:54:37 -0700
From:   Jue Wang <juew@...gle.com>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Borislav Petkov <bp@...en8.de>, dinghui@...gfor.com.cn,
        huangcun@...gfor.com.cn, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>, Oscar Salvador <osalvador@...e.de>,
        x86 <x86@...nel.org>, "Song, Youquan" <youquan.song@...el.com>
Subject: Re: [PATCH 2/3] x86/mce: Avoid infinite loop for copy from user recovery

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);