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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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