[Xen-devel] [PATCH v7 5/6] memory: add check_get_page_from_gfn() as a wrapper...

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

...for some uses of get_page_from_gfn().

There are many occurences of the following pattern in the code:

    q = <readonly look-up> ? P2M_ALLOC : P2M_UNSHARE;
    page = get_page_from_gfn(d, gfn, &p2mt, q);

    if ( p2m_is_paging(p2mt) )
    {
        if ( page )
            put_page(page);

        p2m_mem_paging_populate(d, gfn);
        return <-EAGAIN or equivalent>;
    }

    if ( (q & P2M_UNSHARE) && p2m_is_shared(p2mt) )
    {
        if ( page )
            put_page(page);

        return <-EAGAIN or equivalent>;
    }

    if ( !page )
        return <-EINVAL or equivalent>;

    if ( !p2m_is_ram(p2mt) ||
         (!<readonly look-up> && p2m_is_readonly(p2mt)) )
    {
        put_page(page);
        return <-EINVAL or equivalent>;
    }

There are some small differences between the exact way the occurences
are coded but the desired semantic is the same.

This patch introduces a new common implementation of this code in
check_get_page_from_gfn() and then converts the various open-coded patterns
into calls to this new function.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>

v7:
 - Fix ARM build by introducing p2m_is_readonly() predicate.
 - Re-name get_paged_frame() -> check_get_page_from_gfn().
 - Adjust default cases of callers switch-ing on return value.

v3:
 - Addressed comments from George.

v2:
 - New in v2.
---
 xen/arch/x86/hvm/emulate.c | 34 ++++++++--------------------
 xen/arch/x86/hvm/hvm.c     | 16 ++-----------
 xen/common/grant_table.c   | 39 ++++++++++----------------------
 xen/common/memory.c        | 56 +++++++++++++++++++++++++++++++++++++---------
 xen/include/asm-arm/p2m.h  |  8 +++++++
 xen/include/asm-x86/p2m.h  |  2 ++
 6 files changed, 79 insertions(+), 76 deletions(-)

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index a577685dc6..0135272bf4 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -353,33 +353,17 @@ static int hvmemul_do_io_buffer(
 
 static int hvmemul_acquire_page(unsigned long gmfn, struct page_info **page)
 {
-    struct domain *curr_d = current->domain;
-    p2m_type_t p2mt;
-
-    *page = get_page_from_gfn(curr_d, gmfn, &p2mt, P2M_UNSHARE);
-
-    if ( *page == NULL )
-        return X86EMUL_UNHANDLEABLE;
-
-    if ( p2m_is_paging(p2mt) )
-    {
-        put_page(*page);
-        p2m_mem_paging_populate(curr_d, gmfn);
-        return X86EMUL_RETRY;
-    }
-
-    if ( p2m_is_shared(p2mt) )
+    switch ( check_get_page_from_gfn(current->domain, _gfn(gmfn), false,
+                                     NULL, page) )
     {
-        put_page(*page);
+    case 0:
+        break;
+    case -EAGAIN:
         return X86EMUL_RETRY;
-    }
-
-    /* This code should not be reached if the gmfn is not RAM */
-    if ( p2m_is_mmio(p2mt) )
-    {
-        domain_crash(curr_d);
-
-        put_page(*page);
+    default:
+        ASSERT_UNREACHABLE();
+        /* Fallthrough */
+    case -EINVAL:
         return X86EMUL_UNHANDLEABLE;
     }
 
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 062872cb71..695d23516a 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2555,24 +2555,12 @@ static void *_hvm_map_guest_frame(unsigned long gfn, 
bool_t permanent,
                                   bool_t *writable)
 {
     void *map;
-    p2m_type_t p2mt;
     struct page_info *page;
     struct domain *d = current->domain;
+    p2m_type_t p2mt;
 
-    page = get_page_from_gfn(d, gfn, &p2mt,
-                             writable ? P2M_UNSHARE : P2M_ALLOC);
-    if ( (p2m_is_shared(p2mt) && writable) || !page )
-    {
-        if ( page )
-            put_page(page);
-        return NULL;
-    }
-    if ( p2m_is_paging(p2mt) )
-    {
-        put_page(page);
-        p2m_mem_paging_populate(d, gfn);
+    if ( check_get_page_from_gfn(d, _gfn(gfn), !writable, &p2mt, &page) )
         return NULL;
-    }
 
     if ( writable )
     {
diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index 0f0b7b1a49..8f888056ff 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -374,39 +374,24 @@ static int get_paged_frame(unsigned long gfn, mfn_t *mfn,
                            struct page_info **page, bool readonly,
                            struct domain *rd)
 {
-    int rc = GNTST_okay;
-    p2m_type_t p2mt;
-
-    *mfn = INVALID_MFN;
-    *page = get_page_from_gfn(rd, gfn, &p2mt,
-                              readonly ? P2M_ALLOC : P2M_UNSHARE);
-    if ( !*page )
-    {
-#ifdef P2M_SHARED_TYPES
-        if ( p2m_is_shared(p2mt) )
-            return GNTST_eagain;
-#endif
-#ifdef P2M_PAGES_TYPES
-        if ( p2m_is_paging(p2mt) )
-        {
-            p2m_mem_paging_populate(rd, gfn);
-            return GNTST_eagain;
-        }
-#endif
-        return GNTST_bad_page;
-    }
+    int rc;
 
-    if ( p2m_is_foreign(p2mt) )
+    rc = check_get_page_from_gfn(rd, _gfn(gfn), readonly, NULL, page);
+    switch ( rc )
     {
-        put_page(*page);
-        *page = NULL;
-
+    case 0:
+        break;
+    case -EAGAIN:
+        return GNTST_eagain;
+    default:
+        ASSERT_UNREACHABLE();
+        /* Fallthrough */
+    case -EINVAL:
         return GNTST_bad_page;
     }
 
     *mfn = page_to_mfn(*page);
-
-    return rc;
+    return GNTST_okay;
 }
 
 static inline void
diff --git a/xen/common/memory.c b/xen/common/memory.c
index 85611ddae4..e289c414f8 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -1625,37 +1625,73 @@ void destroy_ring_for_helper(
     }
 }
 
-int prepare_ring_for_helper(
-    struct domain *d, unsigned long gmfn, struct page_info **_page,
-    void **_va)
+/*
+ * Acquire a pointer to struct page_info for a specified doman and GFN,
+ * checking whether the page has been paged out, or needs unsharing.
+ * If the function succeeds then zero is returned and page_p is written
+ * with a pointer to the struct page_info with a reference taken. The
+ * caller is responsible for dropping the reference. If p2mt_p is non-NULL
+ * then it is also written with the P2M type of the page.
+ * If the function fails then an appropriate errno is returned and the
+ * values referenced by page_p and p2mt_p are undefined.
+ */
+int check_get_page_from_gfn(struct domain *d, gfn_t gfn, bool readonly,
+                            p2m_type_t *p2mt_p, struct page_info **page_p)
 {
-    struct page_info *page;
+    p2m_query_t q = readonly ? P2M_ALLOC : P2M_UNSHARE;
     p2m_type_t p2mt;
-    void *va;
+    struct page_info *page;
 
-    page = get_page_from_gfn(d, gmfn, &p2mt, P2M_UNSHARE);
+    page = get_page_from_gfn(d, gfn_x(gfn), &p2mt, q);
 
 #ifdef CONFIG_HAS_MEM_PAGING
     if ( p2m_is_paging(p2mt) )
     {
         if ( page )
             put_page(page);
-        p2m_mem_paging_populate(d, gmfn);
-        return -ENOENT;
+
+        p2m_mem_paging_populate(d, gfn_x(gfn));
+        return -EAGAIN;
     }
 #endif
 #ifdef CONFIG_HAS_MEM_SHARING
-    if ( p2m_is_shared(p2mt) )
+    if ( (q & P2M_UNSHARE) && p2m_is_shared(p2mt) )
     {
         if ( page )
             put_page(page);
-        return -ENOENT;
+
+        return -EAGAIN;
     }
 #endif
 
     if ( !page )
         return -EINVAL;
 
+    if ( !p2m_is_ram(p2mt) || (!readonly && p2m_is_readonly(p2mt)) )
+    {
+        put_page(page);
+        return -EINVAL;
+    }
+
+    if ( p2mt_p )
+        *p2mt_p = p2mt;
+
+    *page_p = page;
+    return 0;
+}
+
+int prepare_ring_for_helper(
+    struct domain *d, unsigned long gmfn, struct page_info **_page,
+    void **_va)
+{
+    struct page_info *page;
+    void *va;
+    int rc;
+
+    rc = check_get_page_from_gfn(d, _gfn(gmfn), false, NULL, &page);
+    if ( rc )
+        return (rc == -EAGAIN) ? -ENOENT : rc;
+
     if ( !get_page_type(page, PGT_writable_page) )
     {
         put_page(page);
diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
index 8823707c17..04f9a7b86b 100644
--- a/xen/include/asm-arm/p2m.h
+++ b/xen/include/asm-arm/p2m.h
@@ -137,12 +137,17 @@ typedef enum {
 #define P2M_GRANT_TYPES (p2m_to_mask(p2m_grant_map_rw) |  \
                          p2m_to_mask(p2m_grant_map_ro))
 
+/* Read-only types */
+#define P2M_RO_TYPES (p2m_to_mask(p2m_ram_ro) |         \
+                      p2m_to_mask(p2m_grant_map_ro))
+
 /* Useful predicates */
 #define p2m_is_ram(_t) (p2m_to_mask(_t) & P2M_RAM_TYPES)
 #define p2m_is_foreign(_t) (p2m_to_mask(_t) & p2m_to_mask(p2m_map_foreign))
 #define p2m_is_any_ram(_t) (p2m_to_mask(_t) &                   \
                             (P2M_RAM_TYPES | P2M_GRANT_TYPES |  \
                              p2m_to_mask(p2m_map_foreign)))
+#define p2m_is_readonly(_t) (p2m_to_mask(_t) & P2M_RO_TYPES)
 
 static inline
 void p2m_altp2m_check(struct vcpu *v, uint16_t idx)
@@ -303,6 +308,9 @@ static inline struct page_info *get_page_from_gfn(
     return page;
 }
 
+int check_get_page_from_gfn(struct domain *d, gfn_t gfn, bool readonly,
+                            p2m_type_t *p2mt_p, struct page_info **page_p);
+
 int get_page_type(struct page_info *page, unsigned long type);
 bool is_iomem_page(mfn_t mfn);
 static inline int get_page_and_type(struct page_info *page,
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index d4b3cfcb6e..03897b49c3 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -492,6 +492,8 @@ static inline struct page_info *get_page_from_gfn(
     return mfn_valid(_mfn(gfn)) && get_page(page, d) ? page : NULL;
 }
 
+int check_get_page_from_gfn(struct domain *d, gfn_t gfn, bool readonly,
+                            p2m_type_t *p2mt_p, struct page_info **page_p);
 
 /* General conversion function from mfn to gfn */
 static inline unsigned long mfn_to_gfn(struct domain *d, mfn_t mfn)
-- 
2.11.0


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