On 6/26/22 23:16, Kai Huang wrote: > On Fri, 2022-06-24 at 12:40 -0700, Dave Hansen wrote: >>> +/* >>> + * 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(). Why not just entirely remove the lower 1MB from the memblock structure on TDX systems? Do something equivalent to adding this on the kernel command line: memmap=1M$0x0 > 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. I think it doesn't like the if().
