linux-kernel - Re: [PATCH v5 07/22] x86/virt/tdx: Implement SEAMCALL function

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Date:   Tue, 26 Jul 2022 17:50:43 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     seanjc@...gle.com, pbonzini@...hat.com, len.brown@...el.com,
        tony.luck@...el.com, rafael.j.wysocki@...el.com,
        reinette.chatre@...el.com, dan.j.williams@...el.com,
        peterz@...radead.org, ak@...ux.intel.com,
        kirill.shutemov@...ux.intel.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        isaku.yamahata@...el.com
Subject: Re: [PATCH v5 07/22] x86/virt/tdx: Implement SEAMCALL function

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.

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.