linux-kernel - Re: [PATCH] tdx, memory hotplug: Check whole hot-adding memory range for TDX

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Message-ID: <96fd7bd9-3525-44e0-b797-55d4e82f9c37@redhat.com>
Date: Tue, 1 Oct 2024 09:54:45 +0200
From: David Hildenbrand <david@...hat.com>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, x86@...nel.org,
 Andrew Morton <akpm@...ux-foundation.org>, Oscar Salvador
 <osalvador@...e.de>, linux-coco@...ts.linux.dev, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Dan Williams <dan.j.williams@...el.com>,
 Kai Huang <kai.huang@...el.com>, "H. Peter Anvin" <hpa@...or.com>,
 Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH] tdx, memory hotplug: Check whole hot-adding memory range
 for TDX

> Because only TDX compatible memory can be used for TDX guest.  The buddy
> is used to allocate memory for TDX guest.  While devdax will not be used
> for that.
> 
>>> This also makes the original TDX memory hotplug notifier useless, so
>>> delete it.
>>
>> The online-notifier would even be too late when used with the
>> memmap-on-memory feature I assume, as we might be touching that memory
>> even before being able to call memory online notifiers.
> 
> This should be OK.  Because we will not use the memory for TDX guest in
> this way.

Thanks for the reminder, I keep assuming that we are hotplugging memory 
into the guest, not the hypervisor.

Having that as a comment in tdx_check_hotplug_memory_range() would be 
helpful: we don't allow mixture of TDX and !TDX memory in the buddy so 
we won't run into trouble when launching encrypted VMs that really need 
TDX-capable memory.

-- 
Cheers,

David / dhildenb