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    SubjectRe: [PATCH v5 12/22] x86/virt/tdx: Convert all memory regions in memblock to TDX memory
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    > > > +/*
    > > > + * Walks over all memblock memory regions that are intended to be
    > > > + * converted to TDX memory. Essentially, it is all memblock memory
    > > > + * regions excluding the low memory below 1MB.
    > > > + *
    > > > + * This is because on some TDX platforms the low memory below 1MB is
    > > > + * not included in CMRs. Excluding the low 1MB can still guarantee
    > > > + * that the pages managed by the page allocator are always TDX memory,
    > > > + * as the low 1MB is reserved during kernel boot and won't end up to
    > > > + * the ZONE_DMA (see reserve_real_mode()).
    > > > + */
    > > > +#define memblock_for_each_tdx_mem_pfn_range(i, p_start, p_end, p_nid) \
    > > > + for_each_mem_pfn_range(i, MAX_NUMNODES, p_start, p_end, p_nid) \
    > > > + if (!pfn_range_skip_lowmem(p_start, p_end))
    > >
    > > Let's summarize where we are at this point:
    > >
    > > 1. All RAM is described in memblocks
    > > 2. Some memblocks are reserved and some are free
    > > 3. The lower 1MB is marked reserved
    > > 4. for_each_mem_pfn_range() walks all reserved and free memblocks, so we
    > > have to exclude the lower 1MB as a special case.
    > >
    > > That seems superficially rather ridiculous. Shouldn't we just pick a
    > > memblock iterator that skips the 1MB? Surely there is such a thing.
    >
    > Perhaps you are suggesting we should always loop the _free_ ranges so we don't
    > need to care about the first 1MB which is reserved?
    >
    > The problem is some reserved memory regions are actually later freed to the page
    > allocator, for example, initrd. So to cover all those 'late-freed-reserved-
    > regions', I used for_each_mem_pfn_range(), instead of for_each_free_mem_range().
    >
    > Btw, I do have a checkpatch warning around this code:
    >
    > ERROR: Macros with complex values should be enclosed in parentheses
    > #109: FILE: arch/x86/virt/vmx/tdx/tdx.c:377:
    > +#define memblock_for_each_tdx_mem_pfn_range(i, p_start, p_end, p_nid) \
    > + for_each_mem_pfn_range(i, MAX_NUMNODES, p_start, p_end, p_nid) \
    > + if (!pfn_range_skip_lowmem(p_start, p_end))
    >
    > But it looks like a false positive to me.

    Hi Dave,

    Sorry to ping. Just double check, any comments around here, ..

    >
    > > Or, should we be doing something different with the 1MB in the memblock
    > > structure?
    >
    > memblock APIs are used by other kernel components. I don't think we should
    > modify memblock code behaviour for TDX. Do you have any specific suggestion?
    >
    > One possible option I can think is explicitly "register" memory regions as TDX
    > memory when they are firstly freed to the page allocator.

    [...]

    >
    > This will require new data structures to represent TDX memblock and the code to
    > create, insert and merge contiguous TDX memblocks, etc. The advantage is we can
    > just iterate those TDX memblocks when constructing TDMRs.
    >
    >

    And here?

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