On Tue, Jan 07, 2025 at 03:42:52PM +0800, Zhenhua Huang wrote:
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index e2739b69e11b..5e0f514de870 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -42,9 +42,11 @@
> #include <asm/pgalloc.h>
> #include <asm/kfence.h>
>
> -#define NO_BLOCK_MAPPINGS BIT(0)
> -#define NO_CONT_MAPPINGS BIT(1)
> -#define NO_EXEC_MAPPINGS BIT(2) /* assumes FEAT_HPDS is not used */
> +#define NO_PMD_BLOCK_MAPPINGS BIT(0)
> +#define NO_PUD_BLOCK_MAPPINGS BIT(1) /* Hotplug case: do not want block mapping for PUD */
> +#define NO_BLOCK_MAPPINGS (NO_PMD_BLOCK_MAPPINGS | NO_PUD_BLOCK_MAPPINGS)
Nit: please use a tab instead of space before (NO_PMD_...)
> +#define NO_CONT_MAPPINGS BIT(2)
> +#define NO_EXEC_MAPPINGS BIT(3) /* assumes FEAT_HPDS is not used */
>
> u64 kimage_voffset __ro_after_init;
> EXPORT_SYMBOL(kimage_voffset);
> @@ -254,7 +256,7 @@ static void init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end,
>
> /* try section mapping first */
> if (((addr | next | phys) & ~PMD_MASK) == 0 &&
> - (flags & NO_BLOCK_MAPPINGS) == 0) {
> + (flags & NO_PMD_BLOCK_MAPPINGS) == 0) {
> pmd_set_huge(pmdp, phys, prot);
>
> /*
> @@ -356,10 +358,11 @@ static void alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end,
>
> /*
> * For 4K granule only, attempt to put down a 1GB block
> + * Hotplug case: do not attempt 1GB block
> */
I don't think we need this comment added here. The hotplug case is a
decision of the caller, so better to have the comment there.
> if (pud_sect_supported() &&
> ((addr | next | phys) & ~PUD_MASK) == 0 &&
> - (flags & NO_BLOCK_MAPPINGS) == 0) {
> + (flags & NO_PUD_BLOCK_MAPPINGS) == 0) {
> pud_set_huge(pudp, phys, prot);
Nit: something wrong with the alignment here. I think the unmodified
line after the 'if' one above was misaligned before your patch.
>
> /*
> @@ -1175,9 +1178,21 @@ int __meminit vmemmap_check_pmd(pmd_t *pmdp, int node,
> int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
> struct vmem_altmap *altmap)
> {
> + unsigned long start_pfn;
> + struct mem_section *ms;
> +
> WARN_ON((start < VMEMMAP_START) || (end > VMEMMAP_END));
>
> - if (!IS_ENABLED(CONFIG_ARM64_4K_PAGES))
> + start_pfn = page_to_pfn((struct page *)start);
> + ms = __pfn_to_section(start_pfn);
Hmm, it would have been better if the core code provided the start pfn
as it does for vmemmap_populate_compound_pages() but I'm fine with
deducting it from 'start'.
> + /*
> + * Hotplugged section does not support hugepages as
> + * PMD_SIZE (hence PUD_SIZE) section mapping covers
> + * struct page range that exceeds a SUBSECTION_SIZE
> + * i.e 2MB - for all available base page sizes.
> + */
> + if (!IS_ENABLED(CONFIG_ARM64_4K_PAGES) || !early_section(ms))
> return vmemmap_populate_basepages(start, end, node, altmap);
> else
> return vmemmap_populate_hugepages(start, end, node, altmap);
> @@ -1339,9 +1354,25 @@ int arch_add_memory(int nid, u64 start, u64 size,
> struct mhp_params *params)
> {
> int ret, flags = NO_EXEC_MAPPINGS;
> + unsigned long start_pfn = page_to_pfn((struct page *)start);
> + struct mem_section *ms = __pfn_to_section(start_pfn);
This looks wrong. 'start' here is a physical address, you want
PFN_DOWN() instead.
>
> VM_BUG_ON(!mhp_range_allowed(start, size, true));
>
> + /* should not be invoked by early section */
> + WARN_ON(early_section(ms));
> +
> + /*
> + * 4K base page's PMD_SIZE matches SUBSECTION_SIZE i.e 2MB. Hence
> + * PMD section mapping can be allowed, but only for 4K base pages.
> + * Where as PMD_SIZE (hence PUD_SIZE) for other page sizes exceed
> + * SUBSECTION_SIZE.
> + */
> + if (IS_ENABLED(CONFIG_ARM64_4K_PAGES))
> + flags |= NO_PUD_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
In theory we can allow contiguous PTE mappings but not PMD. You could
probably do the same as a NO_BLOCK_MAPPINGS and split it into multiple
components - NO_PTE_CONT_MAPPINGS and so on.
> + else
> + flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
Similarly with 16K/64K pages we can allow contiguous PTEs as they all go
up to 2MB blocks.
I think we should write the flags setup in a more readable way than
trying to do mental maths on the possible combinations, something like:
flags = NO_PUD_BLOCK_MAPPINGS | NO_PMD_CONT_MAPPINGS;
if (SUBSECTION_SHIFT < PMD_SHIFT)
flags |= NO_PMD_BLOCK_MAPPINGS;
if (SUBSECTION_SHIFT < CONT_PTE_SHIFT)
flags |= NO_PTE_CONT_MAPPINGS;
This way we don't care about the page size and should cover any changes
to SUBSECTION_SHIFT making it smaller than 2MB.
--
Catalin
