xen/arch/x86: fix TXT AP gate placement and MONITOR/MWAIT race#27
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accek-itl wants to merge 2 commits intoTrenchBoot:aem-staging-2026-03-13from
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xen/arch/x86: fix TXT AP gate placement and MONITOR/MWAIT race#27accek-itl wants to merge 2 commits intoTrenchBoot:aem-staging-2026-03-13from
accek-itl wants to merge 2 commits intoTrenchBoot:aem-staging-2026-03-13from
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The gate needs to be before non-target APs attempt to access (uninitialized) per-cpu data, which is a save to cpu_info.cr4 field in .L_after_stack_setup. Signed-off-by: Szymon Acedański <accek@invisiblethingslab.com> Assisted-by: Claude:claude-opus-4-6
The wait condition needs to be re-checked after MONITOR and before MWAIT to avoid the deadlock when the trigger happens between an earlier condition check and the MONITOR instruction. Signed-off-by: Szymon Acedański <accek@invisiblethingslab.com> Assisted-by: Claude:claude-opus-4-6
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Tested on DELL Optiplex 7010 (UEFI), Xen + Trenchboot works and boots, PCRs 17 and 18 are extended |
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I think for upstreaming these changes could be squashed into this commit: 8b76786, though this commit message part will no longer hold: |
| * __high_start in parallel, so we gate non-target APs. | ||
| * | ||
| * In non-TXT boot APs wake one-by-one via SIPI. | ||
| */ |
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I would explain that this serializes APs initialization to force them waking up in accordance with the order in which BSP expects them to wake up. Could also mention STACK_CPUINFO_FIELD() below which necessitates doing it here.
| cpu_relax(); | ||
| } | ||
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| unsigned int txt_booting_apicid; |
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This data is int in other places and I think it can be static.
Suggested change
| unsigned int txt_booting_apicid; | |
| static int txt_booting_apicid; |
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Two fixes for the TXT AP gate needed after upstream changes:
Tested by booting Trenchboot-XEN on Asus LCL laptop (aem-staging-2026-03-13-accek branch which included these commits) and verifying PCRs 17, 18 are non-zero.
Related issue: TrenchBoot/trenchboot-issues#82