Re: [PATCH v15 08/23] x86/virt/tdx: Use all system memory when initializing TDX module as TDX memory

[Nikolay Borisov]

On 5.12.24 г. 9:57 ч., Mike Rapoport wrote:
> Hi,
>
> I've been auditing for_each_mem_pfn_range() users and it's usage in TDX is
> dubious for me.
>
> On Fri, Nov 10, 2023 at 12:55:45AM +1300, Kai Huang wrote:
> > As TDX-usable memory is a fixed configuration, take a snapshot of the
> > memory configuration from memblocks at the time of module initialization
> > (memblocks are modified on memory hotplug).  This snapshot is used to
>
> AFAUI this could happen long after free_initmem() which discards all
> memblock data on x86.
> >> enable TDX support for *this* memory configuration only.  Use a memory
> > hotplug notifier to ensure that no other RAM can be added outside of
> > this configuration.
>   
> ...
>
> > +/*
> > + * Ensure that all memblock memory regions are convertible to TDX
> > + * memory.  Once this has been established, stash the memblock
> > + * ranges off in a secondary structure because memblock is modified
> > + * in memory hotplug while TDX memory regions are fixed.
> > + */
> > +static int build_tdx_memlist(struct list_head *tmb_list)
> > +{
> > +	unsigned long start_pfn, end_pfn;
> > +	int i, ret;
> > +
> > +	for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, NULL) {
>
> Unles ARCH_KEEP_MEMBLOCK is defined this won't work after free_initmem()

TDX_HOST actually selects ARCH_KEEP_MEMBLOCK:

  6 config INTEL_TDX_HOST 

   5         bool "Intel Trust Domain Extensions (TDX) host support" 

   4         depends on CPU_SUP_INTEL 

   3         depends on X86_64 

   2         depends on KVM_INTEL 

   1         depends on X86_X2APIC 

1980         select ARCH_KEEP_MEMBLOCK 

   1         depends on CONTIG_ALLOC 

   2         depends on !KEXEC_CORE 

   3         depends on X86_MCE


<snip>