On Tue, Mar 11, 2025 at 04:45:26PM +0100, David Woodhouse wrote:
> On Thu, 2025-02-13 at 15:24 +0100, Greg Kroah-Hartman wrote:
> > 6.13-stable review patch. If anyone has any objections, please let me know.
> >
> > ------------------
> >
> > From: David Woodhouse <dwmw@xxxxxxxxxxxx>
> >
> > [ Upstream commit 4b5bc2ec9a239bce261ffeafdd63571134102323 ]
> >
> > Now that the following fix:
> >
> > d0ceea662d45 ("x86/mm: Add _PAGE_NOPTISHADOW bit to avoid updating userspace page tables")
> >
> > stops kernel_ident_mapping_init() from scribbling over the end of a
> > 4KiB PGD by assuming the following 4KiB will be a userspace PGD,
> > there's no good reason for the kexec PGD to be part of a single
> > 8KiB allocation with the control_code_page.
> >
> > ( It's not clear that that was the reason for x86_64 kexec doing it that
> > way in the first place either; there were no comments to that effect and
> > it seems to have been the case even before PTI came along. It looks like
> > it was just a happy accident which prevented memory corruption on kexec. )
> >
> > Either way, it definitely isn't needed now. Just allocate the PGD
> > separately on x86_64, like i386 already does.
>
> No objection (which is just as well given how late I am in replying)
> but I'm just not sure *why*. This doesn't fix a real bug; it's just a
> cleanup.
>
> Does this mean I should have written my original commit message better,
> to make it clearer that this *isn't* a bugfix?
Yes, that's why it was picked up.
