[PATCH v5 3/4] arm64: Implement page table free interfaces
From: Will Deacon <hidden>
Date: 2018-03-27 18:00:48
Also in:
linux-arch, lkml
Hi Chintan, On Tue, Mar 27, 2018 at 06:54:59PM +0530, Chintan Pandya wrote:
quoted hunk ↗ jump to hunk
Implement pud_free_pmd_page() and pmd_free_pte_page(). Implementation requires, 1) Freeing of the un-used next level page tables 2) Clearing off the current pud/pmd entry 3) Invalidate TLB which could have previously valid but not stale entry Signed-off-by: Chintan Pandya <redacted> --- V4->V5: - Using __flush_tlb_kernel_pgtable instead of flush_tlb_kernel_range arch/arm64/mm/mmu.c | 33 +++++++++++++++++++++++++++++++-- 1 file changed, 31 insertions(+), 2 deletions(-)diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index da98828..3552c7a 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c@@ -45,6 +45,7 @@ #include <asm/memblock.h> #include <asm/mmu_context.h> #include <asm/ptdump.h> +#include <asm/tlbflush.h> #define NO_BLOCK_MAPPINGS BIT(0) #define NO_CONT_MAPPINGS BIT(1)@@ -973,12 +974,40 @@ int pmd_clear_huge(pmd_t *pmdp) return 1; } +static int __pmd_free_pte_page(pmd_t *pmd, unsigned long addr, bool tlb_inv) +{ + pmd_t *table; + + if (pmd_val(*pmd)) {
Please can you follow what I did in 20a004e7b017 ("arm64: mm: Use
READ_ONCE/WRITE_ONCE when accessing page tables") and:
1. Use consistent naming, so pmd_t * pmdp.
2. Use READ_ONCE to dereference the entry once into a local.
Similarly for the pud code below.
+ table = __va(pmd_val(*pmd)); + pmd_clear(pmd); + if (tlb_inv) + __flush_tlb_kernel_pgtable(addr); + + free_page((unsigned long) table);
Hmm. Surely it's only safe to call free_page if !tlb_inv in situations when the page table is already disconnected at a higher level? That doesn't appear to be the case with the function below, which still has the pud installed. What am I missing?
+ }
+ return 1;
+}
+
int pud_free_pmd_page(pud_t *pud, unsigned long addr)
{
- return pud_none(*pud);
+ pmd_t *table;
+ int i;
+
+ if (pud_val(*pud)) {
+ table = __va(pud_val(*pud));
+ for (i = 0; i < PTRS_PER_PMD; i++)
+ __pmd_free_pte_page(&table[i], addr + (i * PMD_SIZE),
+ false);
+
+ pud_clear(pud);
+ flush_tlb_kernel_range(addr, addr + PUD_SIZE);Why aren't you using __flush_tlb_kernel_pgtable here? Will