Received-SPF: pass (google.com: domain of linux-kernel+bounces-49913-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Date: Fri, 2 Feb 2024 14:39:11 +0100
From: Borislav Petkov <bp@alien8.de>
To: Tong Tiangen <tongtiangen@huawei.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
	wangkefeng.wang@huawei.com,
	Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
	"H. Peter Anvin" <hpa@zytor.com>, Tony Luck <tony.luck@intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Naoya Horiguchi <naoya.horiguchi@nec.com>,
	linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org,
	linux-mm@kvack.org, Guohanjun <guohanjun@huawei.com>
Subject: Re: [PATCH -next v4 2/3] x86/mce: rename MCE_IN_KERNEL_COPYIN to
 MCE_IN_KERNEL_COPY_MC
Message-ID: <20240202133911.GBZbzwf-M37M-J3EJX@fat_crate.local>
References: <20240111135548.3207437-1-tongtiangen@huawei.com>
 <20240111135548.3207437-3-tongtiangen@huawei.com>
 <20240131070258.GGZbnwov0g918F-FGz@fat_crate.local>
 <3009aadd-69d6-c797-20b4-95cf926b6dd9@huawei.com>
 <20240201142016.GFZbuooG9CRoK90U2C@fat_crate.local>
 <39c1e4d2-b1d0-91ae-595e-1add4698dd7f@huawei.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <39c1e4d2-b1d0-91ae-595e-1add4698dd7f@huawei.com>

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