[PATCH RFC 0/4] crash_dump: recover from machine checks in copy_oldmem_page()

[Christian Brauner]

On Thu, Nov 12, 2026 at 05:37:06PM +0100, Christian Brauner wrote:
> A capture kernel reads the memory of the crashed kernel. That memory
> may have uncorrectable errors in it. Which is likely also what murdered
> the first kernel.
> 
> On x86 a machine check in the copy that /proc/vmcore does out of an old
> page panics the capture kernel. On book3s64 the read() comes up short
> and splice() panics. Breno has observed that on a fleet iiuc. The first
> kernel dies of a machine check and then there's no vmcore either.
> 
> I had the powerpc half of this as a fix in part 1 of the procfs series
> because Chris ran into it there. Breno pointed out that x86 has the same
> hole.
> 
> I think that likely makes this a kdump problem and not a procfs problem.
> So I moved this out together with the ioremap_cache() fix.

So I'm not super familiar with the machine check stuff. I know that
@Linus has some familiarity with this. So I guess a yay or nay would be
nice. Not sure if really a localized fix for the architectures that have
mc support makes more sense. A common helper seems less fragile to me.