[ipxe-devel] [ipxe/ipxe] [efi] Claim SNP devices early in efi_download_start() (#120)

[Michael Brown]

Claiming the SNP devices has the side effect of raising the TPL to
iPXE's normal operating level of TPL_CALLBACK (see the commit message
for c89a446 ("[efi] Run at TPL_CALLBACK to protect against UEFI
timers") for details).  This must happen before executing any code
that relies upon the TPL having been raised to TPL_CALLBACK.

The call to efi_snp_claim() in efi_download_start() currently happens
only after the call to xfer_open().  Calling xfer_open() will
typically result in a retry timer being started, which will result in
a call to currticks() in order to initialise the timer.  The call to
currticks() will drop to TPL_APPLICATION and restore to TPL_CALLBACK
in order to allow a timer tick to occur.  Since this call happened
before the call to efi_snp_claim(), the restored TPL is incorrect.

This in turn results in efi_snp_claim() recording the incorrect
original TPL, causing efi_snp_release() to eventually restore the
incorrect TPL, causing the system to lock up when ExitBootServices()
is called at TPL_CALLBACK.

Fix by moving the call to efi_snp_claim() to the start of
efi_download_start().

Debugged-by: Jarrod Johnson <jjohnson2 at lenovo.com>
Debugged-by: He He4 Huang <huanghe4 at lenovo.com>
Signed-off-by: Michael Brown <mcb30 at ipxe.org>
You can view, comment on, or merge this pull request online at:

  https://github.com/ipxe/ipxe/pull/120

-- Commit Summary --

  * [efi] Claim SNP devices early in efi_download_start()

-- File Changes --

    M src/interface/efi/efi_download.c (5)

-- Patch Links --

https://github.com/ipxe/ipxe/pull/120.patch
https://github.com/ipxe/ipxe/pull/120.diff

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