Re: [PATCH] x86/efi: update e820 about reserved EFI boot services data to fix kexec breakage

Ard Biesheuvel
2019-12-04T10:24:08Z

On Wed, 4 Dec 2019 at 10:14, Ingo Molnar <mingo@kernel.org> wrote:
>
>
> * Dave Young <dyoung@redhat.com> wrote:
>
> > On 12/04/19 at 03:52pm, Dave Young wrote:
> > > Michael Weiser reported he got below error during a kexec rebooting:
> > > esrt: Unsupported ESRT version 2904149718861218184.
> > >
> > > The ESRT memory stays in EFI boot services data, and it was reserved
> > > in kernel via efi_mem_reserve(). The initial purpose of the reservation
> > > is to reuse the EFI boot services data across kexec reboot. For example
> > > the BGRT image data and some ESRT memory like Michael reported.
> > >
> > > But although the memory is reserved it is not updated in X86 e820 table.
> > > And kexec_file_load iterate system ram in io resource list to find places
> > > for kernel, initramfs and other stuff. In Michael's case the kexec loaded
> > > initramfs overwritten the ESRT memory and then the failure happened.
> >
> > s/overwritten/overwrote :) If need a repost please let me know..
> >
> > >
> > > Since kexec_file_load depends on the e820 to be updated, just fix this
> > > by updating the reserved EFI boot services memory as reserved type in e820.
> > >
> > > Originally any memory descriptors with EFI_MEMORY_RUNTIME attribute are
> > > bypassed in the reservation code path because they are assumed as reserved.
> > > But the reservation is still needed for multiple kexec reboot.
> > > And it is the only possible case we come here thus just drop the code
> > > chunk then everything works without side effects.
> > >
> > > On my machine the ESRT memory sits in an EFI runtime data range, it does
> > > not trigger the problem, but I successfully tested with BGRT instead.
> > > both kexec_load and kexec_file_load work and kdump works as well.
> > >
> > > Signed-off-by: Dave Young <dyoung@redhat.com>
>
>
> So I edited this to:
>
> From: Dave Young <dyoung@redhat.com>
>
> Michael Weiser reported he got this error during a kexec rebooting:
>
> esrt: Unsupported ESRT version 2904149718861218184.
>
> The ESRT memory stays in EFI boot services data, and it was reserved
> in kernel via efi_mem_reserve(). The initial purpose of the reservation
> is to reuse the EFI boot services data across kexec reboot. For example
> the BGRT image data and some ESRT memory like Michael reported.
>
> But although the memory is reserved it is not updated in the X86 E820 table,
> and kexec_file_load() iterates system RAM in the IO resource list to find places
> for kernel, initramfs and other stuff. In Michael's case the kexec loaded
> initramfs overwrote the ESRT memory and then the failure happened.
>
> Since kexec_file_load() depends on the E820 table being updated, just fix this
> by updating the reserved EFI boot services memory as reserved type in E820.
>
> Originally any memory descriptors with EFI_MEMORY_RUNTIME attribute are
> bypassed in the reservation code path because they are assumed as reserved.
>
> But the reservation is still needed for multiple kexec reboots,
> and it is the only possible case we come here thus just drop the code
> chunk, then everything works without side effects.
>
> On my machine the ESRT memory sits in an EFI runtime data range, it does
> not trigger the problem, but I successfully tested with BGRT instead.
> both kexec_load() and kexec_file_load() work and kdump works as well.
>

Acked-by: Ard Biesheuvel <ardb@kernel.org>