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    SubjectRe: [PATCH v7 10/20] x86/virt/tdx: Use all system memory when initializing TDX module as TDX memory
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    On 28.11.22 09:38, Huang, Kai wrote:
    > On Fri, 2022-11-25 at 10:28 +0100, David Hildenbrand wrote:
    >> 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.
    >
    > Hi David,
    >
    > Thanks for the review!
    >
    > Right. The memmap pages are added to the zone before online_pages(), but IIUC
    > those memmap pages will never be free pages thus won't be allocated by the page
    > allocator, correct? Therefore in practice there won't be problem even they are
    > not TDX compatible memory.

    But that memory will be read/written. Isn't that an issue, for example,
    if memory doesn't get accepted etc?

    --
    Thanks,

    David / dhildenb

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