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

Mike Rapoport
2024-12-05T07:57:57Z

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()

> + /*
> + * The first 1MB is not reported as TDX convertible memory.
> + * Although the first 1MB is always reserved and won't end up
> + * to the page allocator, it is still in memblock's memory
> + * regions. Skip them manually to exclude them as TDX memory.
> + */
> + start_pfn = max(start_pfn, PHYS_PFN(SZ_1M));
> + if (start_pfn >= end_pfn)
> + continue;
> +
> + /*
> + * Add the memory regions as TDX memory. The regions in
> + * memblock has already guaranteed they are in address
> + * ascending order and don't overlap.
> + */
> + ret = add_tdx_memblock(tmb_list, start_pfn, end_pfn);
> + if (ret)
> + goto err;
> + }
> +
> + return 0;
> +err:
> + free_tdx_memlist(tmb_list);
> + return ret;
> +}
> +
> static int init_tdx_module(void)
> {
> + int ret;
> +
> + /*
> + * To keep things simple, assume that all TDX-protected memory
> + * will come from the page allocator. Make sure all pages in the
> + * page allocator are TDX-usable memory.
> + *
> + * Build the list of "TDX-usable" memory regions which cover all
> + * pages in the page allocator to guarantee that. Do it while
> + * holding mem_hotplug_lock read-lock as the memory hotplug code
> + * path reads the @tdx_memlist to reject any new memory.
> + */
> + get_online_mems();
> +
> + ret = build_tdx_memlist(&tdx_memlist);
> + if (ret)
> + goto out_put_tdxmem;
> +
> /*
> * TODO:
> *
> - * - Build the list of TDX-usable memory regions.
> * - Get TDX module "TD Memory Region" (TDMR) global metadata.
> * - Construct a list of TDMRs to cover all TDX-usable memory
> * regions.
> @@ -168,7 +267,14 @@ static int init_tdx_module(void)
> *
> * Return error before all steps are done.
> */
> - return -EINVAL;
> + ret = -EINVAL;
> +out_put_tdxmem:
> + /*
> + * @tdx_memlist is written here and read at memory hotplug time.
> + * Lock out memory hotplug code while building it.
> + */
> + put_online_mems();
> + return ret;
> }
>
> static int __tdx_enable(void)
> @@ -258,6 +364,56 @@ static int __init record_keyid_partitioning(u32 *tdx_keyid_start,
> return 0;
> }
>
> +static bool is_tdx_memory(unsigned long start_pfn, unsigned long end_pfn)
> +{
> + struct tdx_memblock *tmb;
> +
> + /*
> + * This check assumes that the start_pfn<->end_pfn range does not
> + * cross multiple @tdx_memlist entries. A single memory online
> + * event across multiple memblocks (from which @tdx_memlist
> + * entries are derived at the time of module initialization) is
> + * not possible. This is because memory offline/online is done
> + * on granularity of 'struct memory_block', and the hotpluggable
> + * memory region (one memblock) must be multiple of memory_block.
> + */
> + list_for_each_entry(tmb, &tdx_memlist, list) {
> + if (start_pfn >= tmb->start_pfn && end_pfn <= tmb->end_pfn)
> + return true;
> + }
> + return false;
> +}
> +
> +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;
> +
> + /*
> + * Empty list means TDX isn't enabled. Allow any memory
> + * to go online.
> + */
> + if (list_empty(&tdx_memlist))
> + return NOTIFY_OK;
> +
> + /*
> + * The TDX memory configuration is static and can not be
> + * changed. Reject onlining any memory which is outside of
> + * the static configuration whether it supports TDX or not.
> + */
> + if (is_tdx_memory(mn->start_pfn, mn->start_pfn + mn->nr_pages))
> + return NOTIFY_OK;
> +
> + return NOTIFY_BAD;
> +}
> +
> +static struct notifier_block tdx_memory_nb = {
> + .notifier_call = tdx_memory_notifier,
> +};
> +
> static int __init tdx_init(void)
> {
> u32 tdx_keyid_start, nr_tdx_keyids;
> @@ -281,6 +437,13 @@ static int __init tdx_init(void)
> return -ENODEV;
> }
>
> + err = register_memory_notifier(&tdx_memory_nb);
> + if (err) {
> + pr_err("initialization failed: register_memory_notifier() failed (%d)\n",
> + err);
> + return -ENODEV;
> + }
> +
> /*
> * Just use the first TDX KeyID as the 'global KeyID' and
> * leave the rest for TDX guests.
> diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
> index a3c52270df5b..c11e0a7ca664 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.h
> +++ b/arch/x86/virt/vmx/tdx/tdx.h
> @@ -27,4 +27,10 @@ enum tdx_module_status_t {
> TDX_MODULE_ERROR
> };
>
> +struct tdx_memblock {
> + struct list_head list;
> + unsigned long start_pfn;
> + unsigned long end_pfn;
> +};
> +
> #endif
> --
> 2.41.0
>

--
Sincerely yours,
Mike.