[RFC PATCH 7/7] x86/mm: Remove vmalloc faulting

Joerg Roedel
2020-05-08T14:41:02Z

From: Joerg Roedel <jroedel@suse.de>

Remove fault handling on vmalloc areas, as the vmalloc code now takes
care of synchronizing changes to all page-tables in the system.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/include/asm/switch_to.h | 23 ------
arch/x86/kernel/setup_percpu.c | 6 +-
arch/x86/mm/fault.c | 134 -------------------------------
arch/x86/mm/pti.c | 8 +-
4 files changed, 4 insertions(+), 167 deletions(-)

diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index 0e059b73437b..9f69cc497f4b 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -12,27 +12,6 @@ struct task_struct *__switch_to_asm(struct task_struct *prev,
__visible struct task_struct *__switch_to(struct task_struct *prev,
struct task_struct *next);

-/* This runs runs on the previous thread's stack. */
-static inline void prepare_switch_to(struct task_struct *next)
-{
-#ifdef CONFIG_VMAP_STACK
- /*
- * If we switch to a stack that has a top-level paging entry
- * that is not present in the current mm, the resulting #PF will
- * will be promoted to a double-fault and we'll panic. Probe
- * the new stack now so that vmalloc_fault can fix up the page
- * tables if needed. This can only happen if we use a stack
- * in vmap space.
- *
- * We assume that the stack is aligned so that it never spans
- * more than one top-level paging entry.
- *
- * To minimize cache pollution, just follow the stack pointer.
- */
- READ_ONCE(*(unsigned char *)next->thread.sp);
-#endif
-}
-
asmlinkage void ret_from_fork(void);

/*
@@ -67,8 +46,6 @@ struct fork_frame {

#define switch_to(prev, next, last) \
do { \
- prepare_switch_to(next); \
- \
((last) = __switch_to_asm((prev), (next))); \
} while (0)

diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index e6d7894ad127..fd945ce78554 100644
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -287,9 +287,9 @@ void __init setup_per_cpu_areas(void)
/*
* Sync back kernel address range again. We already did this in
* setup_arch(), but percpu data also needs to be available in
- * the smpboot asm. We can't reliably pick up percpu mappings
- * using vmalloc_fault(), because exception dispatch needs
- * percpu data.
+ * the smpboot asm and arch_sync_kernel_mappings() doesn't sync to
+ * swapper_pg_dir on 32-bit. The per-cpu mappings need to be available
+ * there too.
*
* FIXME: Can the later sync in setup_cpu_entry_areas() replace
* this call?
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 255fc631b042..dffe8e4d3140 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -214,44 +214,6 @@ void arch_sync_kernel_mappings(unsigned long start, unsigned long end)
}
}

-/*
- * 32-bit:
- *
- * Handle a fault on the vmalloc or module mapping area
- */
-static noinline int vmalloc_fault(unsigned long address)
-{
- unsigned long pgd_paddr;
- pmd_t *pmd_k;
- pte_t *pte_k;
-
- /* Make sure we are in vmalloc area: */
- if (!(address >= VMALLOC_START && address < VMALLOC_END))
- return -1;
-
- /*
- * Synchronize this task's top level page-table
- * with the 'reference' page table.
- *
- * Do _not_ use "current" here. We might be inside
- * an interrupt in the middle of a task switch..
- */
- pgd_paddr = read_cr3_pa();
- pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
- if (!pmd_k)
- return -1;
-
- if (pmd_large(*pmd_k))
- return 0;
-
- pte_k = pte_offset_kernel(pmd_k, address);
- if (!pte_present(*pte_k))
- return -1;
-
- return 0;
-}
-NOKPROBE_SYMBOL(vmalloc_fault);
-
/*
* Did it hit the DOS screen memory VA from vm86 mode?
*/
@@ -316,79 +278,6 @@ static void dump_pagetable(unsigned long address)

#else /* CONFIG_X86_64: */

-/*
- * 64-bit:
- *
- * Handle a fault on the vmalloc area
- */
-static noinline int vmalloc_fault(unsigned long address)
-{
- pgd_t *pgd, *pgd_k;
- p4d_t *p4d, *p4d_k;
- pud_t *pud;
- pmd_t *pmd;
- pte_t *pte;
-
- /* Make sure we are in vmalloc area: */
- if (!(address >= VMALLOC_START && address < VMALLOC_END))
- return -1;
-
- /*
- * Copy kernel mappings over when needed. This can also
- * happen within a race in page table update. In the later
- * case just flush:
- */
- pgd = (pgd_t *)__va(read_cr3_pa()) + pgd_index(address);
- pgd_k = pgd_offset_k(address);
- if (pgd_none(*pgd_k))
- return -1;
-
- if (pgtable_l5_enabled()) {
- if (pgd_none(*pgd)) {
- set_pgd(pgd, *pgd_k);
- arch_flush_lazy_mmu_mode();
- } else {
- BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_k));
- }
- }
-
- /* With 4-level paging, copying happens on the p4d level. */
- p4d = p4d_offset(pgd, address);
- p4d_k = p4d_offset(pgd_k, address);
- if (p4d_none(*p4d_k))
- return -1;
-
- if (p4d_none(*p4d) && !pgtable_l5_enabled()) {
- set_p4d(p4d, *p4d_k);
- arch_flush_lazy_mmu_mode();
- } else {
- BUG_ON(p4d_pfn(*p4d) != p4d_pfn(*p4d_k));
- }
-
- BUILD_BUG_ON(CONFIG_PGTABLE_LEVELS < 4);
-
- pud = pud_offset(p4d, address);
- if (pud_none(*pud))
- return -1;
-
- if (pud_large(*pud))
- return 0;
-
- pmd = pmd_offset(pud, address);
- if (pmd_none(*pmd))
- return -1;
-
- if (pmd_large(*pmd))
- return 0;
-
- pte = pte_offset_kernel(pmd, address);
- if (!pte_present(*pte))
- return -1;
-
- return 0;
-}
-NOKPROBE_SYMBOL(vmalloc_fault);
-
#ifdef CONFIG_CPU_SUP_AMD
static const char errata93_warning[] =
KERN_ERR
@@ -1227,29 +1116,6 @@ do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code,
*/
WARN_ON_ONCE(hw_error_code & X86_PF_PK);

- /*
- * We can fault-in kernel-space virtual memory on-demand. The
- * 'reference' page table is init_mm.pgd.
- *
- * NOTE! We MUST NOT take any locks for this case. We may
- * be in an interrupt or a critical region, and should
- * only copy the information from the master page table,
- * nothing more.
- *
- * Before doing this on-demand faulting, ensure that the
- * fault is not any of the following:
- * 1. A fault on a PTE with a reserved bit set.
- * 2. A fault caused by a user-mode access. (Do not demand-
- * fault kernel memory due to user-mode accesses).
- * 3. A fault caused by a page-level protection violation.
- * (A demand fault would be on a non-present page which
- * would have X86_PF_PROT==0).
- */
- if (!(hw_error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) {
- if (vmalloc_fault(address) >= 0)
- return;
- }
-
/* Was the fault spurious, caused by lazy TLB invalidation? */
if (spurious_kernel_fault(hw_error_code, address))
return;
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 843aa10a4cb6..da0fb17a1a36 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -448,13 +448,7 @@ static void __init pti_clone_user_shared(void)
* the sp1 and sp2 slots.
*
* This is done for all possible CPUs during boot to ensure
- * that it's propagated to all mms. If we were to add one of
- * these mappings during CPU hotplug, we would need to take
- * some measure to make sure that every mm that subsequently
- * ran on that CPU would have the relevant PGD entry in its
- * pagetables. The usual vmalloc_fault() mechanism would not
- * work for page faults taken in entry_SYSCALL_64 before RSP
- * is set up.
+ * that it's propagated to all mms.
*/

unsigned long va = (unsigned long)&per_cpu(cpu_tss_rw, cpu);
--
2.17.1