Re: [PATCHv3 15/17] x86/mm: Implement sync_direct_mapping()

Dave Hansen
2018-06-18T16:28:32Z

> index 17383f9677fa..032b9a1ba8e1 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -731,6 +731,8 @@ kernel_physical_mapping_init(unsigned long paddr_start,
> pgd_changed = true;
> }
>
> + sync_direct_mapping();
> +
> if (pgd_changed)
> sync_global_pgds(vaddr_start, vaddr_end - 1);
>
> @@ -1142,10 +1144,13 @@ void __ref vmemmap_free(unsigned long start, unsigned long end,
> static void __meminit
> kernel_physical_mapping_remove(unsigned long start, unsigned long end)
> {
> + int ret;
> start = (unsigned long)__va(start);
> end = (unsigned long)__va(end);
>
> remove_pagetable(start, end, true, NULL);
> + ret = sync_direct_mapping();
> + WARN_ON(ret);
> }

I understand why you implemented it this way, I really do. It's
certainly the quickest way to hack something together and make a
standalone piece of code. But, I don't think it's maintainable.

For instance, this call to sync_direct_mapping() could be entirely
replaced by a call to:

for_each_keyid(k)...
remove_pagetable(start + offset_per_keyid * k,
end + offset_per_keyid * k,
true, NULL);

No?

> int __ref arch_remove_memory(u64 start, u64 size, struct vmem_altmap *altmap)
> @@ -1290,6 +1295,7 @@ void mark_rodata_ro(void)
> (unsigned long) __va(__pa_symbol(rodata_end)),
> (unsigned long) __va(__pa_symbol(_sdata)));
>
> + sync_direct_mapping();
> debug_checkwx();

Huh, checking the return code in some cases and not others. Curious.
Why is it that way?