Messages in this thread | | | Date | Sat, 25 Mar 2023 09:25:36 -0700 | Subject | Re: [PATCH] x86: Disable kexec for TDX guests | From | Dave Hansen <> |
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On 3/25/23 09:01, Kirill A. Shutemov wrote: > The last item is tricky. TDX guests use ACPI MADT MPWK to bring up > secondary CPUs. The mechanism doesn't allow to put a CPU back offline if > it has woken up. ... > +int arch_kexec_load(void) > +{ > + if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) { > + pr_warn_once("Disable kexec: not yet supported in TDX guest\n"); > + return -EOPNOTSUPP; > + } > + > + return 0; > +}
So, let's put all this together:
1. TDX implementations use MADT for wakeup exclusively right now (but are not necessarily _required_ to do so forever) 2. MADT doesn't support CPU offlining 3. kexec() requires offlining
Thus, current TDX implementations can't support TDX guests. This *doesn't* say that TDX will always use the MADT for wakeups.
Yet, the check you have here is for TDX and *not* for the MADT.
That seems wrong.
Let's say SEV or arm64 comes along and uses the MADT for their guests. They'll add another arch_kexec_load(), with a check for *their* feature.
This all seems like you should be disabling kexec() the moment the MADT CPU wakeup is used instead of making it based on TDX.
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