linux-kernel - Re: [PATCH -next v4 2/3] x86/mce: rename MCE_IN_KERNEL_COPYIN to MCE_IN_KERNEL_COPY

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Date: Fri, 2 Feb 2024 14:39:11 +0100
From: Borislav Petkov <bp@...en8.de>
To: Tong Tiangen <tongtiangen@...wei.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	wangkefeng.wang@...wei.com,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Naoya Horiguchi <naoya.horiguchi@....com>,
	linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
	linux-mm@...ck.org, Guohanjun <guohanjun@...wei.com>
Subject: Re: [PATCH -next v4 2/3] x86/mce: rename MCE_IN_KERNEL_COPYIN to
 MCE_IN_KERNEL_COPY_MC

On Fri, Feb 02, 2024 at 03:51:12PM +0800, Tong Tiangen wrote:
> Currently, there are some kernel memory copy scenarios is also mc safe
> which use copy_mc_to_kernel() or copy_mc_user_highpage(), these kernel-
> to-kernel copy use fixup_type EX_TYPE_DEFAULT_MCE_SAFE. In these
> scenarios, posion pages need to be isolated too and the current

So you have, for example:

  unsigned long __must_check copy_mc_to_kernel(void *dst, const void *src, unsigned len)

Now imagine you get a MCE for *dst which is some kernel page which
cannot be poisoned: direct map, kernel text, and so on.

Attempting to poison such a page would not work, to put it mildly.

So, again, what *exactly* are you "fixing" here?

When I read "Currently, there are some kernel memory copy scenarios" and
there's nothing more explaining what those scenarios are, I'm tempted to
ignore this completely until you give a detailed and concrete example
what the problem is:

What exactly are you doing, what goes wrong, why does this need to be
fixed and so on...

If there isn't such a real-life use case you're encountering, then this
all is waste of time.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette