Messages in this thread | | | Date | Tue, 04 Jun 2013 13:29:41 +0800 | From | Lingzhu Xiang <> | Subject | Re: [PATCH] Modify UEFI anti-bricking code |
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On 06/02/2013 04:06 AM, Matthew Garrett wrote: > This patch reworks the UEFI anti-bricking code, including an effective > reversion of cc5a080c and 31ff2f20. It turns out that calling > QueryVariableInfo() from boot services results in some firmware > implementations jumping to physical addresses even after entering virtual > mode, so until we have 1:1 mappings for UEFI runtime space this isn't > going to work so well. > > Reverting these gets us back to the situation where we'd refuse to create > variables on some systems because they classify deleted variables as "used" > until the firmware triggers a garbage collection run, which they won't do > until they reach a lower threshold. This results in it being impossible to > install a bootloader, which is unhelpful. > > Feedback from Samsung indicates that the firmware doesn't need more than > 5KB of storage space for its own purposes, so that seems like a reasonable > threshold. However, there's still no guarantee that a platform will attempt > garbage collection merely because it drops below this threshold. It seems > that this is often only triggered if an attempt to write generates a > genuine EFI_OUT_OF_RESOURCES error. We can force that by attempting to > create a variable larger than the remaining space. This should fail, but if > it somehow succeeds we can then immediately delete it. > > I've tested this on the UEFI machines I have available, but I don't have > a Samsung and so can't verify that it avoids the bricking problem.
This patch works well on my Dell Windows 8 logo machine.
This Dell machine will use up ~2K nvram space on each reboot and do garbage collection at boot time when full. With the new 5K threshold, it is only a few reboots away from boot time garbage collection anyway.
Run time garbage collection also works. But the write takes 5 seconds.
Lingzhu Xiang
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