Re: [PATCH v2 02/22] x86/mm: Generalize LDT remap into "mm-local region"

[Dave Hansen]

On 3/20/26 11:23, Brendan Jackman wrote:
>  
> +#ifdef CONFIG_MM_LOCAL_REGION
> +static inline void mm_local_region_free(struct mm_struct *mm)
> +{
> +	if (mm_local_region_used(mm)) {
> +		struct mmu_gather tlb;
> +		unsigned long start = MM_LOCAL_BASE_ADDR;
> +		unsigned long end = MM_LOCAL_END_ADDR;
> +
> +		/*
> +		 * Although free_pgd_range() is intended for freeing user
> +		 * page-tables, it also works out for kernel mappings on x86.
> +		 * We use tlb_gather_mmu_fullmm() to avoid confusing the
> +		 * range-tracking logic in __tlb_adjust_range().
> +		 */
> +		tlb_gather_mmu_fullmm(&tlb, mm);

These are superficial nits and I need to go through this series in
actual detail, but here are the nits:

Indentation is bad. What you have here double-indents the whole function.

Do this:

	struct mmu_gather tlb;
	unsigned long start = MM_LOCAL_BASE_ADDR;
	unsigned long end = MM_LOCAL_END_ADDR;

	if (!mm_local_region_used(mm))
		return;

	... rest of code here

> +		 * We use tlb_gather_mmu_fullmm() to avoid confusing the
> +		 * range-tracking logic in __tlb_adjust_range().
> +		 */

Imperative voice, please.

And a meta-comment:

>  Documentation/arch/x86/x86_64/mm.rst    |   4 +-
>  arch/x86/Kconfig                        |   2 +
>  arch/x86/include/asm/mmu_context.h      | 119 ++++++++++++++++++++++++++++-
>  arch/x86/include/asm/page.h             |  32 ++++++++
>  arch/x86/include/asm/pgtable_32_areas.h |   9 ++-
>  arch/x86/include/asm/pgtable_64_types.h |  12 ++-
>  arch/x86/kernel/ldt.c                   | 130 +++++---------------------------

This is too big and there's too much going on here. This is doing a few
logical things like both introducing mm-local regions *and* making the
LDT remap one of them.