[Xen-devel] [PATCH RFC v2 6/9] xen/arm: Add handling write fault for dirty-page tracing

[Jaeyong Yoo <jaeyong.yoo@xxxxxxxxxxx>]

From: Elena Pyatunina <e.pyatunina@xxxxxxxxxxx>

Add handling write fault in do_trap_data_abort_guest for dirty-page
tracing. Mark dirty function makes the bitmap of dirty pages.

Signed-off-by: Elena Pyatunina <e.pyatunina@xxxxxxxxxxx>
Singed-off-by: Jaeyong Yoo <jaeyong.yoo@xxxxxxxxxxx>
---
 xen/arch/arm/mm.c            | 59 ++++++++++++++++++++++++++++++-
 xen/arch/arm/p2m.c           | 84 ++++++++++++++++++++++++++++++++++++++++++++
 xen/arch/arm/traps.c         |  7 ++++
 xen/include/asm-arm/domain.h |  8 +++++
 xen/include/asm-arm/mm.h     |  2 ++
 xen/include/asm-arm/p2m.h    |  3 ++
 6 files changed, 162 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 650b1fc..f509008 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -680,7 +680,6 @@ void destroy_xen_mappings(unsigned long v, unsigned long e)
     create_xen_entries(REMOVE, v, 0, (e - v) >> PAGE_SHIFT, 0);
 }
 
-enum mg { mg_clear, mg_ro, mg_rw, mg_rx };
 static void set_pte_flags_on_range(const char *p, unsigned long l, enum mg mg)
 {
     lpae_t pte;
@@ -1142,6 +1141,64 @@ int is_iomem_page(unsigned long mfn)
         return 1;
     return 0;
 }
+
+/*
+ * Set l3e entries of P2M table to be read-only.
+ *
+ * On first write, it page faults, its entry is changed to read-write,
+ * and on retry the write succeeds.
+ *
+ * Populate dirty_bitmap by looking for entries that have been
+ * switched to read-write.
+ */
+int handle_page_fault(struct domain *d, paddr_t addr)
+{
+    lpae_t pte, *first = NULL, *second = NULL, *third = NULL;
+    struct p2m_domain *p2m = &d->arch.p2m;
+
+    if ( d->arch.dirty.mode == 0 || first_table_offset(addr) >= LPAE_ENTRIES )
+        return 1;
+
+    spin_lock(&p2m->lock);
+
+    first = __map_domain_page(p2m->first_level);
+
+    if ( !first ||
+         !first[first_table_offset(addr)].walk.valid ||
+         !first[first_table_offset(addr)].walk.table )
+        goto done;
+
+    second = map_domain_page(first[first_table_offset(addr)].walk.base);
+
+    if ( !second ||
+         !second[second_table_offset(addr)].walk.valid ||
+         !second[second_table_offset(addr)].walk.table )
+        goto done;
+
+    third = map_domain_page(second[second_table_offset(addr)].walk.base);
+
+    if ( !third )
+        goto done;
+
+    pte = third[third_table_offset(addr)];
+
+    if (pte.p2m.valid && pte.p2m.write == 0)
+    {
+        mark_dirty(d, addr);
+        pte.p2m.write = 1;
+        write_pte(&third[third_table_offset(addr)], pte);
+        flush_tlb_local();
+    }
+
+done:
+    if (third) unmap_domain_page(third);
+    if (second) unmap_domain_page(second);
+    if (first) unmap_domain_page(first);
+
+    spin_unlock(&p2m->lock);
+    return 0;
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 8bf7eb7..bae7af7 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -412,6 +412,90 @@ unsigned long gmfn_to_mfn(struct domain *d, unsigned long 
gpfn)
     return p >> PAGE_SHIFT;
 }
 
+static struct page_info * new_dirty_page(void)
+{
+    struct page_info *page = NULL;
+    void *p;
+
+    page = alloc_domheap_page(NULL, 0);
+    if ( page == NULL )
+        return NULL;
+
+    p = __map_domain_page(page);
+
+    clear_page(p);
+    unmap_domain_page(p);
+
+    return page;
+}
+
+void mark_dirty(struct domain *d, paddr_t addr)
+{
+    struct page_info *page;
+    xen_pfn_t *first = NULL, *second = NULL, *third = NULL;
+    void *p;
+    int changed;
+
+    spin_lock(&d->arch.dirty.lock);
+
+    if (d->arch.dirty.top == NULL)
+    {
+        page = alloc_domheap_pages(NULL, 1, 0);
+        if (page == NULL)
+        {
+            printk("Error: couldn't allocate page for dirty bitmap!\n");
+            spin_unlock(&d->arch.dirty.lock);
+            return;
+        }
+
+        INIT_PAGE_LIST_HEAD(&d->arch.dirty.pages);
+        page_list_add(page, &d->arch.dirty.pages);
+
+        /* Clear both first level pages */
+        p = __map_domain_page(page);
+        clear_page(p);
+        unmap_domain_page(p);
+
+        p = __map_domain_page(page + 1);
+        clear_page(p);
+        unmap_domain_page(p);
+
+        d->arch.dirty.top = page;
+    }
+
+    first = __map_domain_page(d->arch.dirty.top);
+    BUG_ON(!first && "Can't map first level p2m.");
+    if ( !first[first_table_offset(addr)])
+    {
+        page = new_dirty_page();
+        page_list_add(page, &d->arch.dirty.pages);
+        first[first_table_offset(addr)] = page_to_mfn(page);
+    }
+
+    second = map_domain_page(first[first_table_offset(addr)]);
+    BUG_ON(!second && "Can't map second level p2m.");
+    if (!second[second_table_offset(addr)])
+    {
+        page = new_dirty_page();
+        page_list_add(page, &d->arch.dirty.pages);
+        second[second_table_offset(addr)] = page_to_mfn(page);
+    }
+
+    third = map_domain_page(second[second_table_offset(addr)]);
+    BUG_ON(!third && "Can't map third level p2m.");
+    changed = !__test_and_set_bit(third_table_offset(addr), third);
+    if (changed)
+    {
+        d->arch.dirty.count++;
+    }
+
+    if (third) unmap_domain_page(third);
+    if (second) unmap_domain_page(second);
+    if (first) unmap_domain_page(first);
+
+    spin_unlock(&d->arch.dirty.lock);
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 398d209..9927712 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1011,6 +1011,13 @@ static void do_trap_data_abort_guest(struct 
cpu_user_regs *regs,
     if ( rc == -EFAULT )
         goto bad_data_abort;
 
+    /* handle permission fault on write */
+    if ((dabt.dfsc & 0x3f) == (FSC_FLT_PERM + 3) && dabt.write)
+    {
+        if (handle_page_fault(current->domain, info.gpa) == 0)
+            return;
+    }
+
     if (handle_mmio(&info))
     {
         regs->pc += dabt.len ? 4 : 2;
diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
index cb251cc..3536757 100644
--- a/xen/include/asm-arm/domain.h
+++ b/xen/include/asm-arm/domain.h
@@ -107,6 +107,14 @@ struct arch_domain
         spinlock_t             lock;
     } uart0;
 
+    struct {
+        spinlock_t lock;
+        int mode;
+        unsigned int count;
+        struct page_info *top;
+        struct page_list_head pages;
+    } dirty;
+
 }  __cacheline_aligned;
 
 struct arch_vcpu
diff --git a/xen/include/asm-arm/mm.h b/xen/include/asm-arm/mm.h
index 5e7c5a3..2b961de 100644
--- a/xen/include/asm-arm/mm.h
+++ b/xen/include/asm-arm/mm.h
@@ -327,6 +327,8 @@ static inline void put_page_and_type(struct page_info *page)
     put_page(page);
 }
 
+int handle_page_fault(struct domain *d, paddr_t addr);
+
 #endif /*  __ARCH_ARM_MM__ */
 /*
  * Local variables:
diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
index 379c453..fd5890f 100644
--- a/xen/include/asm-arm/p2m.h
+++ b/xen/include/asm-arm/p2m.h
@@ -110,6 +110,9 @@ static inline int get_page_and_type(struct page_info *page,
     return rc;
 }
 
+enum mg { mg_clear, mg_ro, mg_rw, mg_rx };
+void mark_dirty(struct domain *d, paddr_t addr);
+
 #endif /* _XEN_P2M_H */
 
 /*
-- 
1.8.1.2


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