On 15/10/25 9:35 pm, Kevin Brodsky wrote:
On 15/10/2025 13:27, Linu Cherian wrote:
From: Chaitanya S Prakash chaitanyas.prakash@arm.com
arch_add_memory() is used to hotplug memory into a system but as a part of its implementation it calls __create_pgd_mapping(), which uses pgtable_alloc() in order to build intermediate page tables. As this path was initally only used during early boot pgtable_alloc() is designed to BUG_ON() on failure. However, in the event that memory hotplug is attempted when the system's memory is extremely tight and the allocation were to fail, it would lead to panicking the system, which is not desirable. Hence update __create_pgd_mapping and all it's callers to be non void and propagate -ENOMEM on allocation failure to allow system to fail gracefully.
But during early boot if there is an allocation failure, we want the system to panic, hence create a wrapper around __create_pgd_mapping() called early_create_pgd_mapping() which is designed to panic, if ret is non zero value. All the init calls are updated to use this wrapper rather than the modified __create_pgd_mapping() to restore functionality.
Fixes: 4ab215061554 ("arm64: Add memory hotplug support") Cc: stable@vger.kernel.org Signed-off-by: Chaitanya S Prakash chaitanyas.prakash@arm.com Signed-off-by: Linu Cherian linu.cherian@arm.com
A couple more nits below (sorry I didn't catch them earlier), but otherwise:
Reviewed-by: Kevin Brodsky kevin.brodsky@arm.com
Changelog:
v3:
Fixed a maybe-uninitialized case in alloc_init_pud
Added Fixes tag and CCed stable
Few other trivial cleanups
arch/arm64/mm/mmu.c | 210 ++++++++++++++++++++++++++++---------------- 1 file changed, 132 insertions(+), 78 deletions(-)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index b8d37eb037fc..638cb4df31a9 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -49,6 +49,8 @@ #define NO_CONT_MAPPINGS BIT(1) #define NO_EXEC_MAPPINGS BIT(2) /* assumes FEAT_HPDS is not used */ +#define INVALID_PHYS_ADDR (-1ULL)
- DEFINE_STATIC_KEY_FALSE(arm64_ptdump_lock_key);
u64 kimage_voffset __ro_after_init; @@ -194,11 +196,11 @@ static void init_pte(pte_t *ptep, unsigned long addr, unsigned long end, } while (ptep++, addr += PAGE_SIZE, addr != end); } -static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
unsigned long end, phys_addr_t phys,pgprot_t prot,phys_addr_t (*pgtable_alloc)(enum pgtable_type),int flags)+static int alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
unsigned long end, phys_addr_t phys,pgprot_t prot,phys_addr_t (*pgtable_alloc)(enum pgtable_type),int flags)@@ -213,6 +215,8 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr, pmdval |= PMD_TABLE_PXN; BUG_ON(!pgtable_alloc); pte_phys = pgtable_alloc(TABLE_PTE);
if (pte_phys == INVALID_PHYS_ADDR)return -ENOMEM;@@ -244,12 +248,15 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr, * walker. */ pte_clear_fixmap();
- return 0; }
-static void init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end,
phys_addr_t phys, pgprot_t prot,phys_addr_t (*pgtable_alloc)(enum pgtable_type), int flags)+static int init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end,
phys_addr_t phys, pgprot_t prot,phys_addr_t (*pgtable_alloc)(enum pgtable_type), int flags)- int ret;
Nit: that could be added to the else block instead (makes it clearer it's not used for the final return, that got me confused when re-reading this patch).
+1.
Reviewed-by: Dev Jain dev.jain@arm.com
[...]