Re: SPI Flash Corruption

[Laszlo Ersek <lersek@redhat.com>]

On 09/19/18 16:26, Samah Mansour wrote:
> Hello,
> 
> 
> Our product uses a Baytrail with Minnowboard Max bios firmware ( version
> 0.93). Every now and then we see SPI flash corruption due to power cuts
> while the unit is booting which causes the unit not to boot anymore. After
> investigation we noticed that the VPD area is all FFs (address
> 44000->47DFF0).
> 
> 
> We have noticed that the Bios while booting writes to the flash from
> several places in the code, which is if interrupted most probably is
> causing the corruption.
> 
> 
> Why is the bios writing all these configurations to flash while booting, is
> it to optimize boot time? is it ok if we disable the bios writing to flash
> completely to protect ourselves from corruption?

The firmware is at liberty to write various non-volatile UEFI variables
during boot. Some of those variables are standardized, some others may
be specific to UEFI drivers (with correspondingly private namespace
GUIDs for the variables).

Power loss during flash write (and resultant flash corruption) is
expected. My understanding is that the Fault Tolerant Write protocol /
driver, sitting between the FVB (firmware volume block, i.e. flash)
protocol / driver, and the variable write protocol / driver, implements
a kind of journaling. It is described in the Intel whitepaper

  A Tour Beyond BIOS
  Implementing UEFI Authenticated Variables in SMM with EDKII
  September 2015

My expectation has been that the platform should recover from
interrupted writes. That is, for a single given UEFI variable, you
should either see "before" or "after" status, never "middle". (The
whitepaper says that "Individual variable atomicity" is maintained even
through a failed "reclaim", with the help of FTW.)

If multiple variables should be in sync with each other, that's a
different question. If the variables are not in sync, I think "failure
to boot" may be a reasonable outcome. But, "failure to boot" means a lot
of things, and I hope one should be at least dropped to the setup
utility or the shell. Are you seeing an actual crash?

Laszlo