Re: [PATCH v7 10/20] x86/virt/tdx: Use all system memory when initializing TDX module as TDX memory

[Huang, Kai]

On Thu, 2022-11-24 at 10:26 +0100, Peter Zijlstra wrote:
> On Wed, Nov 23, 2022 at 05:50:37PM -0800, Dan Williams wrote:
> 
> > arch_add_memory() does not add memory to the page allocator.  For
> > example, memremap_pages() uses arch_add_memory() and explicitly does not
> > release the memory to the page allocator. This check belongs in
> > add_memory_resource() to prevent new memory that violates TDX from being
> > onlined. Hopefully there is also an option to disable TDX from the
> > kernel boot command line to recover memory-hotplug without needing to
> > boot into the BIOS to toggle TDX.
> 
> So I've been pushing for all this to either require: tdx=force on the
> cmdline to boot-time enable, or delay all the memory allocation to the
> first KVM/TDX instance being created.
> 
> That is, by default, none of this crud should ever trigger and consume
> memory if you're not using TDX (most of us really).
> 
> (every machine I have loads kvm.ko unconditionally -- even if I never
> user KVM, so kvm.ko load time is not a valid point in time to do TDX
> enablement).
> 

Thanks for input.  I am fine with 'tdx=force'.

Although, I'd like to point out KVM will have a module parameter 'enable_tdx'.

Hi Dave, Sean, do you have any comments?