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

Nikolay Borisov
2024-12-05T09:06:21Z

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>