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

[David Hildenbrand]

On 24.11.22 10:06, Huang, Kai wrote:
> On Wed, 2022-11-23 at 17:50 -0800, Dan Williams wrote:
> > >    
> > > @@ -968,6 +969,15 @@ int arch_add_memory(int nid, u64 start, u64 size,
> > >    	unsigned long start_pfn = start >> PAGE_SHIFT;
> > >    	unsigned long nr_pages = size >> PAGE_SHIFT;
> > >    
> > > +	/*
> > > +	 * For now if TDX is enabled, all pages in the page allocator
> > > +	 * must be TDX memory, which is a fixed set of memory regions
> > > +	 * that are passed to the TDX module.  Reject the new region
> > > +	 * if it is not TDX memory to guarantee above is true.
> > > +	 */
> > > +	if (!tdx_cc_memory_compatible(start_pfn, start_pfn + nr_pages))
> > > +		return -EINVAL;
> >
> > 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.
>
> Indeed.  Sorry I missed this.
>
> > This check belongs in
> > add_memory_resource() to prevent new memory that violates TDX from being
> > onlined.
>
> This would require adding another 'arch_cc_memory_compatible()' to the common
> add_memory_resource() (I actually long time ago had such patch to work with the
> memremap_pages() you mentioned above).
>
> How about adding a memory_notifier to the TDX code, and reject online of TDX
> incompatible memory (something like below)?  The benefit is this is TDX code
> self contained and won't pollute the common mm code:
>
> +static int tdx_memory_notifier(struct notifier_block *nb,
> +                              unsigned long action, void *v)
> +{
> +       struct memory_notify *mn = v;
> +
> +       if (action != MEM_GOING_ONLINE)
> +               return NOTIFY_OK;
> +
> +       /*
> +        * Not all memory is compatible with TDX.  Reject
> +        * online of any incompatible memory.
> +        */
> +       return tdx_cc_memory_compatible(mn->start_pfn,
> +                       mn->start_pfn + mn->nr_pages) ? NOTIFY_OK : NOTIFY_BAD;
> +}
> +
> +static struct notifier_block tdx_memory_nb = {
> +       .notifier_call = tdx_memory_notifier,
> +};

With mhp_memmap_on_memory() some memory might already be touched during 
add_memory() (because part of the hotplug memory is used for holding the 
memmap), not when actually onlining memory. So in that case, this would 
be too late.

add_memory_resource() sounds better, even though I disgust such TDX 
special handling in common code.

--
Thanks,

David / dhildenb