On Thu, 2022-07-07 at 07:26 -0700, Dave Hansen wrote: > 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 I will explore this option. Thanks! > > > 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(). Yes. I'll explore your suggestion above and I hope this can be avoided. -- Thanks, -Kai
