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Subject[Regression v5.19-rc1] crash kexec fails to boot the 2nd kernel (Re: [PATCH v12 38/46] x86/sev: Add SEV-SNP feature detection/setup)
Date
I found crash kexec fails to boot the 2nd kernel since v5.19-rc1 and
git bisect points to this as a bad commit:

commit b190a043c49af4587f5e157053f909192820522a
Author: Michael Roth <michael.roth@amd.com>
Date: Thu Feb 24 10:56:18 2022 -0600

x86/sev: Add SEV-SNP feature detection/setup

Initial/preliminary detection of SEV-SNP is done via the Confidential
Computing blob. Check for it prior to the normal SEV/SME feature
initialization, and add some sanity checks to confirm it agrees with
SEV-SNP CPUID/MSR bits.

The problem seems to occur when find_cc_blob_setup_data() walks setup_data
chain. If the code is modified to do nothing in find_cc_blob_setup_data(),
the 2nd kernel boots fine.

On my system, the chain of setup_data looks like following on regular boot:
setup_data: type=0x3 addr=0x9e9e5018 next=0x9e9dc018
setup_data: type=0x3 addr=0x9e9dc018 next=0x9e9d2018
setup_data: type=0x3 addr=0x9e9d2018 next=0x8a27b018
setup_data: type=0x3 addr=0x8a27b018 next=0x8a218018
setup_data: type=0x3 addr=0x8a218018 next=0x9e9a0018
setup_data: type=0x3 addr=0x9e9a0018 next=0x8a1e6018
setup_data: type=0x3 addr=0x8a1e6018 next=0x8a1b4018
setup_data: type=0x3 addr=0x8a1b4018 next=0x8a182018
setup_data: type=0x3 addr=0x8a182018 next=0x8a056018
setup_data: type=0x3 addr=0x8a056018 next=0x8a020018
setup_data: type=0x3 addr=0x8a020018 next=0x89fea018
setup_data: type=0x3 addr=0x89fea018 next=0x0

OTOH, it looks like following on crash kexec boot:
setup_data: type=0x4 addr=0x2e000000 next=0x0

Other places that parses setup_data uses early_memremap() before
accessing the data (e.g. parse_setup_data()). I wonder if the lack of
remapping causes the problem but find_cc_blob is too early in the
boot process for early_memremap to work.

--
Jun'ichi Nomura, NEC Corporation / NEC Solution Innovators, Ltd.

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