[PATCH v5 13/20] x86/kexec: Mark relocate_kernel page as ROX instead of RWX

[David Woodhouse]

On Thu, 2024-12-12 at 10:42 -0700, Nathan Chancellor wrote:
>  
> > What CPU is this? Shouldn't loading %cr3 have caused the existing TLB
> > entry to be flushed?
> 
> The machine I have mainly been reproducing and testing this issue on is
> an Intel Xeon Gold 6314U but I initially noticed this problem on a few
> consumer AMD and Intel chips that I have locally.
> 
Not on my Haswell Xeon box though, it seems.

Dave Hansen points out that it's probably the _PAGE_GLOBAL bit; that
TLB entry *won't* get flushed.

> > Can you tell me what happens if we don't write through *that* virtual
> > mapping of the page, but instead do it a few instructions later through
> > the identity mapping of the same page (which surely *won't* have an
> > older, non-writeable TLB entry already...)?
> 
> Applying that diff on top of 5a82223e0743 makes the issue go away for
> me.

Thanks. It actually seems to break the preserve_context mode for me, so
I'll give it a bit more thought and probably come back to you with
another version to test.
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