lkml.org 
[lkml]   [2022]   [Oct]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH 8/8] efi: pstore: Add module parameter for setting the record size
    On Fri, 7 Oct 2022 at 15:00, Guilherme G. Piccoli <gpiccoli@igalia.com> wrote:
    >
    > First of all, thanks Ard for the historical explanation!
    >
    >
    > On 07/10/2022 06:11, Ard Biesheuvel wrote:
    > > [...]
    > >> I think it'd be great to make it configurable! Ard, do you have any
    > >> sense of what the max/min, etc, should be here?
    > >>
    > >
    > > Given that dbx on an arbitrary EFI system with secure boot enabled is
    > > already almost 4k, that seems like a reasonable default. As for the
    > > upper bound, there is no way to know what weird firmware bugs you
    > > might tickle by choosing highly unusual values here.
    > >
    > > If you need to store lots of data, you might want to look at [0] for
    > > some work done in the past on using capsule update for preserving data
    > > across a reboot. In the general case, this is not as useful, as the
    > > capsule is only delivered to the firmware after invoking the
    > > ResetSystem() EFI runtime service (as opposed to SetVariable() calls
    > > taking effect immediately). However, if you need to capture large
    > > amounts of data, and can tolerate the uncertainty involved in the
    > > capsule approach, it might be a reasonable option.
    > >
    > > [0] https://lore.kernel.org/all/20200312011335.70750-1-qiuxu.zhuo@intel.com/
    >
    > So, you mean 4K as the default? I can change, but I would try to not
    > mess with the current users, is there a case you can imagine something
    > like 4k would fail? Maybe 2K is safer?
    >

    Reducing the number of writes 4x on systems that can support this has
    its own advantages, so I am willing to risk it.

    > As for the maximum, I've tested with many values, and when it's larger
    > than ~30000 for edk2/ovmf, it fails with EFI_OUT_OF_RESOURCES and
    > doesn't collect the log; other than that, no issues observed.
    >

    OVMF has

    OvmfPkg/OvmfPkgX64.dsc:
    gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000
    OvmfPkg/OvmfPkgX64.dsc:
    gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x8400

    where the first one is without secure boot and the second with secure boot.

    Interestingly, the default is

    gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x400

    so this is probably where this 1k number comes from. So perhaps it is
    better to leave it at 1k after all :-(

    > When set to ~24000, the interesting is that we have fewer big logs in
    > /sys/fs/pstore, so it's nice to see compared to the bunch of 1K files heheh
    >
    > Anyway, let's agree on the default and then I can resubmit that, I'm
    > glad you both consider that it's a good idea =)
    >
    > Thanks,
    >
    >
    > Guilherme

    \
     
     \ /
      Last update: 2022-10-07 15:20    [W:2.631 / U:0.044 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site