linux-kernel - Re: [PATCH v2 2/2] x86, kexec_file_load: make it work with efi=noruntime or efi=old

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Date:   Thu, 17 Jan 2019 16:20:00 +0800
From:   Kairui Song <kasong@...hat.com>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
Cc:     Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, Dave Young <dyoung@...hat.com>,
        Baoquan He <bhe@...hat.com>, kexec@...ts.infradead.org,
        akpm@...ux-foundation.org, robert.moore@...el.com,
        erik.schmauss@...el.com, rafael.j.wysocki@...el.com,
        Len Brown <lenb@...nel.org>
Subject: Re: [PATCH v2 2/2] x86, kexec_file_load: make it work with
 efi=noruntime or efi=old_map

On Thu, Jan 17, 2019 at 3:51 PM Chao Fan <fanc.fnst@...fujitsu.com> wrote:
>
> On Thu, Jan 17, 2019 at 03:41:13PM +0800, Kairui Song wrote:
> >On Wed, Jan 16, 2019 at 5:46 PM Borislav Petkov <bp@...en8.de> wrote:
> >>
> >> On Wed, Jan 16, 2019 at 03:08:42PM +0800, Kairui Song wrote:
> >> > I didn't see a way to reuse things in that patch series, situation is
> >> > different, in that patch it needs to get RSDP in very early boot stage
> >> > so it did everything from scratch, in this patch kexec_file_load need
> >> > to get RSDP too, but everything is well setup so things are a lot
> >> > easier, just read from current boot_prams, efi and fallback to
> >> > acpi_find_root_pointer should be good.
> >>
> >> No no. Early code should find out that venerable RSDP thing once and
> >> will save it somewhere for further use. No gazillion parsings of it.
> >> Just once and share it with the rest of the code that needs it.
> >>
> >
> >How about we refill the boot_params.acpi_rsdp_addr if it is not valid
> >in early code, so it could be used as a reliable RSDP address source?
> >That should make things easier.
>
> I think it's OK.
> Try to read it, if get RSDP, use it.
> If not, search in EFI/BIOS/... and refill the RSDP to
> boot_params.acpi_rsdp_addr.
> By the way, I search kernel code, I didn't find other code fill and
> use it, only you(KEXEC) are trying to fill it.
> If I miss something, please let me know.

Yes, kexec would read RSDP again to pass it to second kernel, and only
if EFI is disabled (efi=noruntime/old_map, else second kernel will get
rsdp just fine). Not sure if any other component would use it.

>
> Thanks,
> Chao Fan

>

--
Best Regards,
Kairui Song