@@ -15,24 +15,6 @@
#define __HAVE_ARCH_PUD_FREE
#include <asm-generic/pgalloc.h>
-/*
- * While riscv platforms with riscv_ipi_for_rfence as true require an IPI to
- * perform TLB shootdown, some platforms with riscv_ipi_for_rfence as false use
- * SBI to perform TLB shootdown. To keep software pagetable walkers safe in this
- * case we switch to RCU based table free (MMU_GATHER_RCU_TABLE_FREE). See the
- * comment below 'ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE' in include/asm-generic/tlb.h
- * for more details.
- */
-static inline void riscv_tlb_remove_ptdesc(struct mmu_gather *tlb, void *pt)
-{
- if (riscv_use_sbi_for_rfence()) {
- tlb_remove_ptdesc(tlb, pt);
- } else {
- pagetable_dtor(pt);
- tlb_remove_page_ptdesc(tlb, pt);
- }
-}
-
static inline void pmd_populate_kernel(struct mm_struct *mm,
pmd_t *pmd, pte_t *pte)
{
@@ -108,14 +90,14 @@ static inline void __pud_free_tlb(struct mmu_gather *tlb, pud_t *pud,
unsigned long addr)
{
if (pgtable_l4_enabled)
- riscv_tlb_remove_ptdesc(tlb, virt_to_ptdesc(pud));
+ tlb_remove_ptdesc(tlb, virt_to_ptdesc(pud));
}
static inline void __p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d,
unsigned long addr)
{
if (pgtable_l5_enabled)
- riscv_tlb_remove_ptdesc(tlb, virt_to_ptdesc(p4d));
+ tlb_remove_ptdesc(tlb, virt_to_ptdesc(p4d));
}
#endif /* __PAGETABLE_PMD_FOLDED */
@@ -143,7 +125,7 @@ static inline pgd_t *pgd_alloc(struct mm_struct *mm)
static inline void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
unsigned long addr)
{
- riscv_tlb_remove_ptdesc(tlb, virt_to_ptdesc(pmd));
+ tlb_remove_ptdesc(tlb, virt_to_ptdesc(pmd));
}
#endif /* __PAGETABLE_PMD_FOLDED */
@@ -151,7 +133,7 @@ static inline void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
static inline void __pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte,
unsigned long addr)
{
- riscv_tlb_remove_ptdesc(tlb, page_ptdesc(pte));
+ tlb_remove_ptdesc(tlb, page_ptdesc(pte));
}
#endif /* CONFIG_MMU */
To support fast gup, the commit 69be3fb111e7 ("riscv: enable MMU_GATHER_RCU_TABLE_FREE for SMP && MMU") did the following: 1) use tlb_remove_page_ptdesc() for those platforms which use IPI to perform TLB shootdown 2) use tlb_remove_ptdesc() for those platforms which use SBI to perform TLB shootdown The tlb_remove_page_ptdesc() is the wrapper of the tlb_remove_page(). By design, the tlb_remove_page() should be used to remove a normal page from a page table entry, and should not be used for page table pages. The tlb_remove_ptdesc() is the wrapper of the tlb_remove_table(), which is designed specifically for freeing page table pages. If the CONFIG_MMU_GATHER_TABLE_FREE is enabled, the tlb_remove_table() will use semi RCU to free page table pages, that is: - batch table freeing: asynchronous free by RCU - single table freeing: IPI + synchronous free If the CONFIG_MMU_GATHER_TABLE_FREE is disabled, the tlb_remove_table() will fall back to pagetable_dtor() + tlb_remove_page(). For case 1), since we need to perform TLB shootdown before freeing the page table page, the local_irq_save() in fast gup can block the freeing and protect the fast gup page walker. Therefore we can ensure safety by just using tlb_remove_page_ptdesc(). In addition, we can also the tlb_remove_ptdesc()/tlb_remove_table() to achieve it, and it doesn't matter whether CONFIG_MMU_GATHER_RCU_TABLE_FREE is selected. And in theory, the performance of freeing pages asynchronously via RCU will not be lower than synchronous free. For case 2), since local_irq_save() only disable S-privilege IPI irq but not M-privilege's, which is used by the SBI implementation to perform TLB shootdown, so we must select CONFIG_MMU_GATHER_RCU_TABLE_FREE and use tlb_remove_ptdesc() to ensure safety. The riscv selects this config for SMP && MMU, the CONFIG_RISCV_SBI is dependent on MMU. Therefore, only the UP system may have the situation where CONFIG_MMU_GATHER_RCU_TABLE_FREE is disabled but CONFIG_RISCV_SBI is enabled. But there is no freeing vs fast gup race in the UP system. So, in summary, we can use tlb_remove_ptdesc() to support fast gup in all cases, and this interface is specifically designed for page table pages. So let's use it unconditionally. Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- arch/riscv/include/asm/pgalloc.h | 26 ++++---------------------- 1 file changed, 4 insertions(+), 22 deletions(-)