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SubjectRe: [PATCH v5 07/22] x86/virt/tdx: Implement SEAMCALL function
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On Tue, 2022-07-26 at 17:50 -0700, Dave Hansen wrote:
> On 7/26/22 17:34, Kai Huang wrote:
> > > This doesn't seem right to me. *If* we get a known-bogus
> > > hot-remove event, we need to reject it. Remember, removal is a
> > > two-step process.
> > If so, we need to reject the (CMR) memory offline. Or we just BUG()
> > in the ACPI memory removal callback?
> >
> > But either way this will requires us to get the CMRs during kernel boot.
>
> I don't get the link there between CMRs at boot and handling hotplug.
>
> We don't need to go to extreme measures just to get a message out of the
> kernel that the BIOS is bad. If we don't have the data to do it
> already, then I don't really see the nee to warn about it.
>
> Think of a system that has TDX enabled in the BIOS, but is running an
> old kernel. It will have *ZERO* idea that hotplug doesn't work. It'll
> run blissfully along. I don't see any reason that a kernel with TDX
> support, but where TDX is disabled should actively go out and try to be
> better than those old pre-TDX kernels.

Agreed, assuming "where TDX is disabled" you mean TDX isn't usable (i.e. when
TDX module isn't loaded, or won't be initialized at all).

>
> Further, there's nothing to stop non-CMR memory from being added to a
> system with TDX enabled in the BIOS but where the kernel is not using
> it. If we actively go out and keep good old DRAM from being added, then
> we unnecessarily addle those systems.
>

OK.

Then for memory hot-add, perhaps we can just go with the "winner-take-all"
approach you mentioned before?

For memory hot-removal, as I replied previously, looks the kernel cannot reject
the removal if it allows memory offline. Any suggestion on this?

--
Thanks,
-Kai


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