[RFC PATCH 08/14] x86/mm: introduce flush_tlb_fix_spurious_fault

[Nadav Amit <nadav.amit@gmail.com>]

From: Nadav Amit <namit@vmware.com>

The next patches introduce relaxed TLB flushes for x86, which would
require a full TLB flush upon spurious page-fault. If a spurious
page-fault occurs on x86, check if the local TLB generation is out of
sync and perform a TLB flush if needed.

Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Nick Piggin <npiggin@gmail.com>
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 arch/x86/include/asm/pgtable.h |  4 +++-
 arch/x86/mm/tlb.c              | 17 +++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 44e2d6f1dbaa..1fbdaff1bb7a 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -1079,7 +1079,9 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm,
 	clear_bit(_PAGE_BIT_RW, (unsigned long *)&ptep->pte);
 }
 
-#define flush_tlb_fix_spurious_fault(vma, address) do { } while (0)
+extern void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma,
+					 unsigned long address);
+#define flush_tlb_fix_spurious_fault flush_tlb_fix_spurious_fault
 
 #define mk_pmd(page, pgprot)   pfn_pmd(page_to_pfn(page), (pgprot))
 
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index d400b6d9d246..ff3bcc55435e 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -955,6 +955,23 @@ static void put_flush_tlb_info(void)
 #endif
 }
 
+void flush_tlb_fix_spurious_fault(struct vm_area_struct *vma,
+				  unsigned long address)
+{
+	u32 loaded_mm_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);
+	u64 mm_tlb_gen = atomic64_read(&vma->vm_mm->context.tlb_gen);
+	u64 local_tlb_gen = this_cpu_read(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen);
+	struct flush_tlb_info *info;
+
+	if (local_tlb_gen == mm_tlb_gen)
+		return;
+
+	preempt_disable();
+	info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, 0, false, 0);
+	flush_tlb_func(info);
+	preempt_enable();
+}
+
 void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
 				unsigned long end, unsigned int stride_shift,
 				bool freed_tables)
-- 
2.25.1