On the arm64 platform with 4K base page config, SECTION_SIZE_BITS is set to 27, making one section 128M. The related page struct which vmemmap points to is 2M then. Commit c1cc1552616d ("arm64: MMU initialisation") optimizes the vmemmap to populate at the PMD section level which was suitable initially since hot plug granule is always one section(128M). However, commit ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") introduced a 2M(SUBSECTION_SIZE) hot plug granule, which disrupted the existing arm64 assumptions.
Considering the vmemmap_free -> unmap_hotplug_pmd_range path, when pmd_sect() is true, the entire PMD section is cleared, even if there is other effective subsection. For example page_struct_map1 and page_strcut_map2 are part of a single PMD entry and they are hot-added sequentially. Then page_struct_map1 is removed, vmemmap_free() will clear the entire PMD entry freeing the struct page map for the whole section, even though page_struct_map2 is still active. Similar problem exists with linear mapping as well, for 16K base page(PMD size = 32M) or 64K base page(PMD = 512M), their block mappings exceed SUBSECTION_SIZE. Tearing down the entire PMD mapping too will leave other subsections unmapped in the linear mapping.
To address the issue, we need to prevent PMD/PUD/CONT mappings for both linear and vmemmap for non-boot sections if corresponding size on the given base page exceeds SUBSECTION_SIZE(2MB now).
Cc: stable@vger.kernel.org # v5.4+ Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") Signed-off-by: Zhenhua Huang quic_zhenhuah@quicinc.com --- Hi Catalin and Anshuman, I have addressed comments so far, please help review. One outstanding point which not finalized is in vmemmap_populate(): how to judge hotplug section. Currently I am using system_state, discussion: https://lore.kernel.org/linux-mm/1515dae4-cb53-4645-8c72-d33b27ede7eb@quicin... arch/arm64/mm/mmu.c | 46 ++++++++++++++++++++++++++++++++++++--------- 1 file changed, 37 insertions(+), 9 deletions(-)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index e2739b69e11b..8718d6e454c5 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -42,9 +42,13 @@ #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) +#define NO_PTE_CONT_MAPPINGS BIT(2) +#define NO_PMD_CONT_MAPPINGS BIT(3) /* Hotplug case: do not want cont mapping for PMD */ +#define NO_CONT_MAPPINGS (NO_PTE_CONT_MAPPINGS | NO_PMD_CONT_MAPPINGS) +#define NO_EXEC_MAPPINGS BIT(4) /* assumes FEAT_HPDS is not used */
u64 kimage_voffset __ro_after_init; EXPORT_SYMBOL(kimage_voffset); @@ -224,7 +228,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
/* use a contiguous mapping if the range is suitably aligned */ if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) && - (flags & NO_CONT_MAPPINGS) == 0) + (flags & NO_PTE_CONT_MAPPINGS) == 0) __prot = __pgprot(pgprot_val(prot) | PTE_CONT);
init_pte(ptep, addr, next, phys, __prot); @@ -254,7 +258,7 @@ 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);
/* @@ -311,7 +315,7 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr,
/* use a contiguous mapping if the range is suitably aligned */ if ((((addr | next | phys) & ~CONT_PMD_MASK) == 0) && - (flags & NO_CONT_MAPPINGS) == 0) + (flags & NO_PMD_CONT_MAPPINGS) == 0) __prot = __pgprot(pgprot_val(prot) | PTE_CONT);
init_pmd(pmdp, addr, next, phys, __prot, pgtable_alloc, flags); @@ -358,8 +362,8 @@ 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 */ if (pud_sect_supported() && - ((addr | next | phys) & ~PUD_MASK) == 0 && - (flags & NO_BLOCK_MAPPINGS) == 0) { + ((addr | next | phys) & ~PUD_MASK) == 0 && + (flags & NO_PUD_BLOCK_MAPPINGS) == 0) { pud_set_huge(pudp, phys, prot);
/* @@ -1177,7 +1181,13 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, { WARN_ON((start < VMEMMAP_START) || (end > VMEMMAP_END));
- if (!IS_ENABLED(CONFIG_ARM64_4K_PAGES)) + /* + * 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) || system_state != SYSTEM_BOOTING) return vmemmap_populate_basepages(start, end, node, altmap); else return vmemmap_populate_hugepages(start, end, node, altmap); @@ -1339,9 +1349,27 @@ int arch_add_memory(int nid, u64 start, u64 size, struct mhp_params *params) { int ret, flags = NO_EXEC_MAPPINGS; + unsigned long start_pfn = PFN_DOWN(start); + struct mem_section *ms = __pfn_to_section(start_pfn);
VM_BUG_ON(!mhp_range_allowed(start, size, true));
+ /* should not be invoked by early section */ + WARN_ON(early_section(ms)); + + /* + * Disallow BlOCK/CONT mappings if the corresponding size exceeds + * SUBSECTION_SIZE which now is 2MB. + * + * PUD_BLOCK or PMD_CONT should consistently exceed SUBSECTION_SIZE + * across all variable page size configurations, so add them directly + */ + 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; + if (can_set_direct_map()) flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
On Thu, Jan 09, 2025 at 05:38:24PM +0800, Zhenhua Huang wrote:
The patch looks fine to me, apart from one nit and a question below:
I don't remember the discussion, do we still need this warning here if the sections are not marked as early? I guess we can keep it if one does an arch_add_memory() on an early section.
I think I suggested to use a WARN_ON_ONCE(!present_section()) but I completely forgot the memory hotplug code paths.
Nit: capital L in BlOCK.
Either way,
Reviewed-by: Catalin Marinas catalin.marinas@arm.com
On 2025/2/13 2:28, Catalin Marinas wrote:
Dear Catalin,
The previous discussion can be found at https://lore.kernel.org/lkml/aedbbc4f-8f6c-46d8-a8d7-53103675a816@quicinc.co..., I highlighted the key points from conversation between me and Anshuman for your reference: "
BTW, shall we remove the check for !early_section since
arch_add_memory is only called during hotplugging case? Correct me please if I'm mistaken :)
While this is true, still might be a good idea to keep the
early_section()
check in place just to be extra careful here. Otherwise an WARN_ON()
might
be needed.
Make sense. I would like to add some comments and WARN_ON() if early_section(). " Regarding your suggestion, I believed it was intended for the vmemmap_populate() function ?(Discussion: https://lore.kernel.org/linux-mm/Z3_d59kp4CuHQp97@arm.com/), but as workflow below indicates: Hot plug: 1. section_activate -> vmemmap_populate 2. mark PRESENT
In contrast, the early flow: 1. memblocks_present -> mark PRESENT 2. __populate_section_memmap -> vmemmap_populate
Could this result in a false warning during hotplugging? I replied with the doubt in above link before but seems you missed :) Could you please share your thoughts if you have a different idea ?
I will include your tags, correct capitalization nit and post one new version.
linux-stable-mirror@lists.linaro.org
-
Catalin Marinas -
Zhenhua Huang