Excerpts from Andrew Morton's message of August 22, 2020 6:14 am:

On Sat, 22 Aug 2020 01:12:09 +1000 Nicholas Piggin [off-list ref] wrote:

quoted

This changes the awkward approach where architectures provide init
functions to determine which levels they can provide large mappings for,
to one where the arch is queried for each call.

This removes code and indirection, and allows constant-folding of dead
code for unsupported levels.

This also adds a prot argument to the arch query. This is unused
currently but could help with some architectures (e.g., some powerpc
processors can't map uncacheable memory with large pages).

--- a/arch/arm64/include/asm/vmalloc.h
+++ b/arch/arm64/include/asm/vmalloc.h

@@ -1,4 +1,12 @@
 #ifndef _ASM_ARM64_VMALLOC_H
 #define _ASM_ARM64_VMALLOC_H
 
+#include <asm/page.h>
+
+#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
+bool arch_vmap_p4d_supported(pgprot_t prot);
+bool arch_vmap_pud_supported(pgprot_t prot);
+bool arch_vmap_pmd_supported(pgprot_t prot);
+#endif

Moving these out of generic code and into multiple arch headers is
unfortunate.  Can we leave them in include/linux/somewhere?  And remove
the ifdefs, if so inclined - they just move the build error from
link-time to compile-time, and such an error shouldn't occur!

Yeah this was just an intermediate step as you saw. It's a bit 
unfortunate, but I thought it made the arch changes clearer.

Thanks,
Nick


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