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

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Date:   Thu, 5 Dec 2019 18:55:45 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-efi@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Michael Weiser <michael@...ser.dinsnail.net>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        kexec@...ts.infradead.org, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/efi: update e820 about reserved EFI boot services
 data to fix kexec breakage

On 12/04/19 at 11:14am, Ingo Molnar wrote:
> 
> * Dave Young <dyoung@...hat.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@...hat.com>
> 
> 
> So I edited this to:
> 
>  From: Dave Young <dyoung@...hat.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.
> 

Thanks for the amending, also thank all for the review and test.

Dave