[PATCH v7 01/12] x86/mm: make MMU_GATHER_RCU_TABLE_FREE unconditional

Rik van Riel
2025-01-23T04:27:24Z

Currently x86 uses CONFIG_MMU_GATHER_TABLE_FREE when using
paravirt, and not when running on bare metal.

There is no real good reason to do things differently for
each setup. Make them all the same.

Currently get_user_pages_fast synchronizes against page table
freeing in two different ways:
- on bare metal, by blocking IRQs, which block TLB flush IPIs
- on paravirt, with MMU_GATHER_RCU_TABLE_FREE

This is done because some paravirt TLB flush implementations
handle the TLB flush in the hypervisor, and will do the flush
even when the target CPU has interrupts disabled.

Always handle page table freeing with MMU_GATHER_RCU_TABLE_FREE.
Using RCU synchronization between page table freeing and get_user_pages_fast()
allows bare metal to also do TLB flushing while interrupts are disabled.

Various places in the mm do still block IRQs or disable preemption
as an implicit way to block RCU frees.

That makes it safe to use INVLPGB on AMD CPUs.

Signed-off-by: Rik van Riel <riel@surriel.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
---
arch/x86/Kconfig | 2 +-
arch/x86/kernel/paravirt.c | 7 +------
arch/x86/mm/pgtable.c | 16 ++++------------
3 files changed, 6 insertions(+), 19 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9d7bd0ae48c4..e8743f8c9fd0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -274,7 +274,7 @@ config X86
select HAVE_PCI
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
- select MMU_GATHER_RCU_TABLE_FREE if PARAVIRT
+ select MMU_GATHER_RCU_TABLE_FREE
select MMU_GATHER_MERGE_VMAS
select HAVE_POSIX_CPU_TIMERS_TASK_WORK
select HAVE_REGS_AND_STACK_ACCESS_API
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index fec381533555..2b78a6b466ed 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -59,11 +59,6 @@ void __init native_pv_lock_init(void)
static_branch_enable(&virt_spin_lock_key);
}

-static void native_tlb_remove_table(struct mmu_gather *tlb, void *table)
-{
- tlb_remove_page(tlb, table);
-}
-
struct static_key paravirt_steal_enabled;
struct static_key paravirt_steal_rq_enabled;

@@ -191,7 +186,7 @@ struct paravirt_patch_template pv_ops = {
.mmu.flush_tlb_kernel = native_flush_tlb_global,
.mmu.flush_tlb_one_user = native_flush_tlb_one_user,
.mmu.flush_tlb_multi = native_flush_tlb_multi,
- .mmu.tlb_remove_table = native_tlb_remove_table,
+ .mmu.tlb_remove_table = tlb_remove_table,

.mmu.exit_mmap = paravirt_nop,
.mmu.notify_page_enc_status_changed = paravirt_nop,
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 5745a354a241..3dc4af1f7868 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -18,14 +18,6 @@ EXPORT_SYMBOL(physical_mask);
#define PGTABLE_HIGHMEM 0
#endif

-#ifndef CONFIG_PARAVIRT
-static inline
-void paravirt_tlb_remove_table(struct mmu_gather *tlb, void *table)
-{
- tlb_remove_page(tlb, table);
-}
-#endif
-
gfp_t __userpte_alloc_gfp = GFP_PGTABLE_USER | PGTABLE_HIGHMEM;

pgtable_t pte_alloc_one(struct mm_struct *mm)
@@ -54,7 +46,7 @@ void ___pte_free_tlb(struct mmu_gather *tlb, struct page *pte)
{
pagetable_pte_dtor(page_ptdesc(pte));
paravirt_release_pte(page_to_pfn(pte));
- paravirt_tlb_remove_table(tlb, pte);
+ tlb_remove_table(tlb, pte);
}

#if CONFIG_PGTABLE_LEVELS > 2
@@ -70,7 +62,7 @@ void ___pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd)
tlb->need_flush_all = 1;
#endif
pagetable_pmd_dtor(ptdesc);
- paravirt_tlb_remove_table(tlb, ptdesc_page(ptdesc));
+ tlb_remove_table(tlb, ptdesc_page(ptdesc));
}

#if CONFIG_PGTABLE_LEVELS > 3
@@ -80,14 +72,14 @@ void ___pud_free_tlb(struct mmu_gather *tlb, pud_t *pud)

pagetable_pud_dtor(ptdesc);
paravirt_release_pud(__pa(pud) >> PAGE_SHIFT);
- paravirt_tlb_remove_table(tlb, virt_to_page(pud));
+ tlb_remove_table(tlb, virt_to_page(pud));
}

#if CONFIG_PGTABLE_LEVELS > 4
void ___p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d)
{
paravirt_release_p4d(__pa(p4d) >> PAGE_SHIFT);
- paravirt_tlb_remove_table(tlb, virt_to_page(p4d));
+ tlb_remove_table(tlb, virt_to_page(p4d));
}
#endif /* CONFIG_PGTABLE_LEVELS > 4 */
#endif /* CONFIG_PGTABLE_LEVELS > 3 */
--
2.47.1