On 1/8/25 00:52, Catalin Marinas wrote:
> 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.
Agreed.
>
>> 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'.
Right, that will require changing arguments in generic vmemmap_populate().
>
>> + /*
>> + * 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.
Agreed.
>
>>
>> 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.
That's a good idea.
>
>> + 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;
Just wondering why not start with PUD level itself ? Although SUBSECTION_SHIFT
might never reach the PUD level but this will help keep the flags calculations
bit simple and ready for all future changes.
flags = 0;
if (SUBSECTION_SHIFT < PUD_SHIFT)
flags |= NO_PUD_BLOCK_MAPPINGS;
if (SUBSECTION_SHIFT < CONT_PMD_SHIFT)
flags |= NO_PMD_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.
>
Agreed.
