On 03/24/17 at 09:08am, Ingo Molnar wrote:
> > Cc: <[email protected]> #4.8+
> > Signed-off-by: Baoquan He <[email protected]>
> > Acked-by: Dave Young <[email protected]>
> > Reviewed-by: Bhupesh Sharma <[email protected]>
> > Acked-by: Thomas Garnier <[email protected]>
> > Cc: Thomas Gleixner <[email protected]>
> > Cc: Ingo Molnar <[email protected]>
> > Cc: "H. Peter Anvin" <[email protected]>
> > Cc: [email protected]
> > Cc: [email protected]
> > Cc: Thomas Garnier <[email protected]>
> > Cc: Kees Cook <[email protected]>
> > Cc: Borislav Petkov <[email protected]>
> > Cc: Andrew Morton <[email protected]>
> > Cc: Masahiro Yamada <[email protected]>
> > Cc: Dave Young <[email protected]>
> > Cc: Bhupesh Sharma <[email protected]>
>
> So I applied this kexec fix and extended the changelog to clearly show why
> this
> fix matters in practice.
I thought it only impacts kexec, but Dave thought it will impact 1st
kenrel either.
>
> Also, to make sure I understood it correctly: these addresses are all dynamic
> on
> 64-bit kernels, i.e. we are establishing and then tearing down these page
> tables
> around EFI calls, and they are 'normally' not present at all, right?
The EFI region is reserved for EFI runtime services virtual mapping, the
original purpose is to preserve this region so that they can be reused
by kexec-ed kernel. This was introduced by Boris in commit d2f7cbe7b26a7
("x86/efi: Runtime services virtual mapping").
So it will be establishing and stay there. According to Dave's telling,
efi will still fetch efi variables or time/date by runtime service by
switching the efi pgd and entering into efi mode. And then switch back
to normal OS. Not sure if I am right for efi part in 1st kernel. For 2nd
kernel, if want to reuse the them, the efi region has to be kept.
Thanks
Baoquan
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