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| author | David Hendricks <dhendrix@chromium.org> | 2019-11-19 19:29:26 -0800 |
|---|---|---|
| committer | Nico Huber <nico.h@gmx.de> | 2019-12-14 15:50:36 +0000 |
| commit | a9d6d1a817ce20e834fe7c354629976e3e5f1108 (patch) | |
| tree | 657071019f73d3b3070be348a73949544e6312b4 /Documentation | |
| parent | 34d07f00b2990bec4a2ce12852acd42c08ddf217 (diff) | |
| download | flashrom-a9d6d1a817ce20e834fe7c354629976e3e5f1108.tar.gz flashrom-a9d6d1a817ce20e834fe7c354629976e3e5f1108.tar.bz2 flashrom-a9d6d1a817ce20e834fe7c354629976e3e5f1108.zip | |
mysteries_intel: Add a section about SMM_BWP
Something to point users to when SMM_BWP might be causing problems.
Change-Id: I394c033e8d4ff96433162f86aefb428d8acf6349
Signed-off-by: David Hendricks <david.hendricks@gmail.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/36986
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/mysteries_intel.txt | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/Documentation/mysteries_intel.txt b/Documentation/mysteries_intel.txt index 10cb37d22..60ad21a76 100644 --- a/Documentation/mysteries_intel.txt +++ b/Documentation/mysteries_intel.txt @@ -5,6 +5,27 @@ A0h), so we have no clue if or where it is on ICH8. Out current policy is to not touch it at all and assume/hope it is 0. += SMM BIOS Write Protection = +Sometimes a hardware vendor will enable "SMM BIOS Write Protect" (SMM_BWP) +in the firmware during boot time. The bits that control SMM_BWP are in the +BIOS_CNTL register in the LPC interface. + +When enabled, the SPI flash can only be written when the system is operating in +in System Management Mode (SMM). In other words, only certain code that was +installed by the BIOS can write to the flash chip. Programs that run in OS +context such as flashrom can still read the flash chip, but cannot write to the +flash chip. + +Flashrom will attempt to detect this and print a warning such as the following: +"Warning: BIOS region SMM protection is enabled!" + +Many vendor-supplied firmware update utilities do not actually write to the ROM; +instead they transfer data to/from memory which is read/written by a routine +running in SMM and is responsible for writing to the firmware ROM. This causes +severe system performance degradataion since all processors must be in SMM +context (ring -2) instead of OS context (ring 0) while the firmware ROM is being +written. + = Accesses beyond region bounds in descriptor mode = Intel's flash image tool will always expand the last region so that it covers the whole flash chip, but some boards ship with a different configuration. |