@@ -271,9 +271,14 @@ static inline pte_t pte_mkdevmap(pte_t pte)
return set_pte_bit(pte, __pgprot(PTE_DEVMAP | PTE_SPECIAL));
}
-static inline void __set_pte(pte_t *ptep, pte_t pte)
+static inline void __set_pte_nosync(pte_t *ptep, pte_t pte)
{
WRITE_ONCE(*ptep, pte);
+}
+
+static inline void __set_pte(pte_t *ptep, pte_t pte)
+{
+ __set_pte_nosync(ptep, pte);
/*
* Only if the new pte is valid and kernel, otherwise TLB maintenance
@@ -178,7 +178,11 @@ static void init_pte(pte_t *ptep, unsigned long addr, unsigned long end,
do {
pte_t old_pte = __ptep_get(ptep);
- __set_pte(ptep, pfn_pte(__phys_to_pfn(phys), prot));
+ /*
+ * Required barriers to make this visible to the table walker
+ * are deferred to the end of alloc_init_cont_pte().
+ */
+ __set_pte_nosync(ptep, pfn_pte(__phys_to_pfn(phys), prot));
/*
* After the PTE entry has been populated once, we
@@ -232,6 +236,11 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
phys += next - addr;
} while (addr = next, addr != end);
+ /*
+ * Note: barriers and maintenance necessary to clear the fixmap slot
+ * ensure that all previous pgtable writes are visible to the table
+ * walker.
+ */
pte_clear_fixmap();
}
After removing uneccessary TLBIs, the next bottleneck when creating the page tables for the linear map is DSB and ISB, which were previously issued per-pte in __set_pte(). Since we are writing multiple ptes in a given pte table, we can elide these barriers and insert them once we have finished writing to the table. Execution time of map_mem(), which creates the kernel linear map page tables, was measured on different machines with different RAM configs: | Apple M2 VM | Ampere Altra| Ampere Altra| Ampere Altra | VM, 16G | VM, 64G | VM, 256G | Metal, 512G ---------------|-------------|-------------|-------------|------------- | ms (%) | ms (%) | ms (%) | ms (%) ---------------|-------------|-------------|-------------|------------- before | 78 (0%) | 435 (0%) | 1723 (0%) | 3779 (0%) after | 11 (-86%) | 161 (-63%) | 656 (-62%) | 1654 (-56%) Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> Tested-by: Itaru Kitayama <itaru.kitayama@fujitsu.com> Tested-by: Eric Chanudet <echanude@redhat.com> --- arch/arm64/include/asm/pgtable.h | 7 ++++++- arch/arm64/mm/mmu.c | 11 ++++++++++- 2 files changed, 16 insertions(+), 2 deletions(-)