linux-kernel - RE: [PATCH] x86/mce: deal with UCE when copy clean pagecache to user space

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Message-ID: <SJ1PR11MB6083DAD269C3ACBE663AF67DFC1EA@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Fri, 26 Sep 2025 16:07:05 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "Wang, Chuanguo" <wangchuanguo@...pur.com>, "bp@...en8.de" <bp@...en8.de>
CC: "tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...hat.com"
	<mingo@...hat.com>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>, "x86@...nel.org" <x86@...nel.org>,
	"hpa@...or.com" <hpa@...or.com>, "linux-edac@...r.kernel.org"
	<linux-edac@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Wang, Chuanguo" <wangchuanguo@...pur.com>
Subject: RE: [PATCH] x86/mce: deal with UCE when copy clean pagecache to user
 space

> Based on copy_from_user, extending the goal to unmap,discard,
> and remap when errors occur in clean pagecache.

This looks to be covering the case where an application does:

	n = read(fd, buf, size);

and the kernel gets a machine check because the data in the page
cache has an uncorrected error, which the kernel consumes while
copying out to user space.

I think this patch solves the immediate problem by avoiding a system
crash from that machine check.

But shouldn't the kernel be able to do better? The page is clean, so
the kernel could drop it from the page cache, allocate a new page,
fill the page by reading from filesystem, and then let the read(2)
syscall resume, copying the freshly acquired copy of the page.

-Tony