linux-kernel - [RFC PATCH 08/14] x86/mm: introduce flush_tlb_fix_spurious

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Message-Id: <20220718120212.3180-9-namit@vmware.com>
Date:   Mon, 18 Jul 2022 05:02:06 -0700
From:   Nadav Amit <nadav.amit@...il.com>
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Nadav Amit <namit@...are.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Nick Piggin <npiggin@...il.com>
Subject: [RFC PATCH 08/14] x86/mm: introduce flush_tlb_fix_spurious_fault

From: Nadav Amit <namit@...are.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@...hat.com>
Cc: Andrew Cooper <andrew.cooper3@...rix.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: David Hildenbrand <david@...hat.com>
Cc: Peter Xu <peterx@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Will Deacon <will@...nel.org>
Cc: Yu Zhao <yuzhao@...gle.com>
Cc: Nick Piggin <npiggin@...il.com>
Signed-off-by: Nadav Amit <namit@...are.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