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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Mon, 30 Dec 2019 01:42:10 -0800
Message-ID: <CAPcyv4hT9HXN2CqZw96zqgdNaapc=9oqSYvGrnEbeqSmx0t5xw@mail.gmail.com>
Subject: Re: [PATCH] x86/efi: update e820 about reserved EFI boot services
 data to fix kexec breakage
To:     Dan Williams <dan.j.williams.korg@gmail.com>
Cc:     Dave Young <dyoung@redhat.com>,
        linux-efi <linux-efi@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Michael Weiser <michael@weiser.dinsnail.net>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        kexec@lists.infradead.org, Ingo Molnar <mingo@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>
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On Sat, Dec 28, 2019 at 10:13 PM Dan Williams <dan.j.williams@intel.com> wrote:
>
> On Sat, Dec 28, 2019 at 12:54 PM Dan Williams
> <dan.j.williams.korg@gmail.com> wrote:
> >
> > On Tue, Dec 3, 2019 at 11:53 PM Dave Young <dyoung@redhat.com> 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.
> > >
> > > 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>
> > > ---
> > >  arch/x86/platform/efi/quirks.c |    6 ++----
> > >  1 file changed, 2 insertions(+), 4 deletions(-)
> > >
> > > --- linux-x86.orig/arch/x86/platform/efi/quirks.c
> > > +++ linux-x86/arch/x86/platform/efi/quirks.c
> > > @@ -260,10 +260,6 @@ void __init efi_arch_mem_reserve(phys_ad
> > >                 return;
> > >         }
> > >
> > > -       /* No need to reserve regions that will never be freed. */
> > > -       if (md.attribute & EFI_MEMORY_RUNTIME)
> > > -               return;
> > > -
> > >         size += addr % EFI_PAGE_SIZE;
> > >         size = round_up(size, EFI_PAGE_SIZE);
> > >         addr = round_down(addr, EFI_PAGE_SIZE);
> > > @@ -293,6 +289,8 @@ void __init efi_arch_mem_reserve(phys_ad
> > >         early_memunmap(new, new_size);
> > >
> > >         efi_memmap_install(new_phys, num_entries);
> > > +       e820__range_update(addr, size, E820_TYPE_RAM, E820_TYPE_RESERVED);
> > > +       e820__update_table(e820_table);
> > >  }
> > >
> > >  /*
> > >
> >
> > Bisect says this change (commit af1648984828) is triggering a
> > regression, likely not urgent, in my testing of the new efi_fake_mem=
> > facility to allow memory to be marked "soft reserved" via the kernel
> > command line (commit 199c84717612 x86/efi: Add efi_fake_mem support
> > for EFI_MEMORY_SP). The following command line triggers the crash
> > signature below:
> >
> >     efi_fake_mem=4G@9G:0x40000,4G@13G:0x40000
> >
> > However, this command line works ok:
> >
> >     efi_fake_mem=8G@9G:0x40000
> >
> > So, something about multiple efi_fake_mem statements interacts badly
> > with this change. Nothing obvious occurs to me at the moment, I'll
> > keep debugging, but wanted to highlight this in the meantime in case
> > someone else sees a deeper issue or the root cause.
>
> Still looking, but this failure does not seem to be specific to the
> "soft reservation" changes. Any update to the efi memmap that pushes
> it over a page boundary triggers this failure. I.e. I can fix the
> problem by over-allocating the efi memmap and then page aligning the
> result. __early_ioremap "should" be handling this case, but it appears
> something else is messing this up.

Found it. Neither this patch nor the soft reservation changes are at
fault, they are just helping to trigger a long standing bug in
efi_fake_memmap(). Its usage of efi_memmap_split_count() can over
count the number of splits needed for new entries. Consider the case
of 2 contiguous fake entries intersecting the end of a single entry.
The first call to efi_memmap_split_count() determines the resulting
split will be (old1, new1, old2), the second call determines (old1,
new2). The result is 2 splits when only 1 is needed to get a result of
(old1, new1, new2) and the new map ends up with an empty entry.
efi_memmap_install() interprets an empty entry as start = 0 end =
0xffffffffffffffff and attempts an extra split / copy past the end of
the new map.

I'll send a patch to fix up efi_fake_memmap().