[Qemu-devel] [PATCH QEMU-XEN v7 4/8] xen: Switch uses of xc_map_foreign_range into xc_map_foreign_pages

[Ian Campbell <ian.campbell@citrix.com>]

In Xen 4.7 we are refactoring parts libxenctrl into a number of
separate libraries which will provide backward and forward API and ABI
compatiblity.

One such library will be libxenforeignmemory which provides access to
privileged foreign mappings and which will provide an interface
equivalent to xc_map_foreign_{pages,bulk}.

In preparation for this switch all uses of xc_map_foreign_range to
xc_map_foreign_pages. This is trivial because size was always
XC_PAGE_SIZE so the necessary adjustments are trivial:

  * Pass &mfn (an array of length 1) instead of mfn. The function
    takes a pointer to const, so there is no possibily of mfn changing
    due to this change.
  * Pass nr_pages=1 instead of size=XC_PAGE_SIZE

There is one wrinkle in xen_console.c:con_initialise() where
con->ring_ref is an int but can in some code paths (when !xendev->dev)
be treated as an mfn. I think this is an existing latent truncation
hazard on platforms where xen_pfn_t is 64-bit and int is 32-bit (e.g.
amd64, both arm* variants). I'm unsure under what circumstances
xendev->dev can be NULL or if anything elsewhere ensures the value
fits into an int. For now I just use a temporary xen_pfn_t to in
effect upcast the pointer from int* to xen_pfn_t*.

In xenfb.c:common_bind we now explicitly launder the mfn into a
xen_pfn_t, so it has the correct type to be passed to
xc_map_foreign_pages and doesn't provoke warnings on 32-bit x86.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
v7: Correct type mismatch (int64 vs xen_pfn_t) on 32 bit x86 in
    xenfb.c, by explicitly laundering via a xen_pfn_t variable.

v6: Switch to xc_map_foreign_pages rather than _bulk. Switching to
    _bulk without checking the value of err[0] risked missing errors.
    The new xenforeignmemory_map coming later in this series will
    DTRT with err==NULL.

    Dropped Stefano's Reviewed-by due to this change.

v4: Ran checkpatch, fixed all errors
    Mention the const-ness of the mfn array in the commit log

fixup!xen: Switch uses of xc_map_foreign_range into xc_map_foreign_pages
---
 hw/char/xen_console.c |  8 ++++----
 hw/display/xenfb.c    | 15 ++++++++-------
 xen-hvm.c             | 14 +++++++-------
 3 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/hw/char/xen_console.c b/hw/char/xen_console.c
index ac1b324..3e8a57b 100644
--- a/hw/char/xen_console.c
+++ b/hw/char/xen_console.c
@@ -228,10 +228,10 @@ static int con_initialise(struct XenDevice *xendev)
 	con->buffer.max_capacity = limit;
 
     if (!xendev->dev) {
-        con->sring = xc_map_foreign_range(xen_xc, con->xendev.dom,
-                                          XC_PAGE_SIZE,
-                                          PROT_READ|PROT_WRITE,
-                                          con->ring_ref);
+        xen_pfn_t mfn = con->ring_ref;
+        con->sring = xc_map_foreign_pages(xen_xc, con->xendev.dom,
+                                         PROT_READ|PROT_WRITE,
+                                         &mfn, 1);
     } else {
         con->sring = xengnttab_map_grant_ref(xendev->gnttabdev, con->xendev.dom,
                                              con->ring_ref,
diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c
index 5e324ef..4a597d7 100644
--- a/hw/display/xenfb.c
+++ b/hw/display/xenfb.c
@@ -95,23 +95,24 @@ struct XenFB {
 
 static int common_bind(struct common *c)
 {
-    uint64_t mfn;
+    uint64_t val;
+    xen_pfn_t mfn;
 
-    if (xenstore_read_fe_uint64(&c->xendev, "page-ref", &mfn) == -1)
+    if (xenstore_read_fe_uint64(&c->xendev, "page-ref", &val) == -1)
 	return -1;
-    assert(mfn == (xen_pfn_t)mfn);
+    mfn = (xen_pfn_t)val;
+    assert(val == mfn);
 
     if (xenstore_read_fe_int(&c->xendev, "event-channel", &c->xendev.remote_port) == -1)
 	return -1;
 
-    c->page = xc_map_foreign_range(xen_xc, c->xendev.dom,
-				   XC_PAGE_SIZE,
-				   PROT_READ | PROT_WRITE, mfn);
+    c->page = xc_map_foreign_pages(xen_xc, c->xendev.dom,
+                                   PROT_READ | PROT_WRITE, &mfn, 1);
     if (c->page == NULL)
 	return -1;
 
     xen_be_bind_evtchn(&c->xendev);
-    xen_be_printf(&c->xendev, 1, "ring mfn %"PRIx64", remote-port %d, local-port %d\n",
+    xen_be_printf(&c->xendev, 1, "ring mfn %"PRI_xen_pfn", remote-port %d, local-port %d\n",
 		  mfn, c->xendev.remote_port, c->xendev.local_port);
 
     return 0;
diff --git a/xen-hvm.c b/xen-hvm.c
index 6680782..2f4e109 100644
--- a/xen-hvm.c
+++ b/xen-hvm.c
@@ -1240,8 +1240,9 @@ int xen_hvm_init(PCMachineState *pcms,
     DPRINTF("buffered io page at pfn %lx\n", bufioreq_pfn);
     DPRINTF("buffered io evtchn is %x\n", bufioreq_evtchn);
 
-    state->shared_page = xc_map_foreign_range(xen_xc, xen_domid, XC_PAGE_SIZE,
-                                              PROT_READ|PROT_WRITE, ioreq_pfn);
+    state->shared_page = xc_map_foreign_pages(xen_xc, xen_domid,
+                                              PROT_READ|PROT_WRITE,
+                                              &ioreq_pfn, 1);
     if (state->shared_page == NULL) {
         hw_error("map shared IO page returned error %d handle=" XC_INTERFACE_FMT,
                  errno, xen_xc);
@@ -1251,8 +1252,8 @@ int xen_hvm_init(PCMachineState *pcms,
     if (!rc) {
         DPRINTF("shared vmport page at pfn %lx\n", ioreq_pfn);
         state->shared_vmport_page =
-            xc_map_foreign_range(xen_xc, xen_domid, XC_PAGE_SIZE,
-                                 PROT_READ|PROT_WRITE, ioreq_pfn);
+            xc_map_foreign_pages(xen_xc, xen_domid, PROT_READ|PROT_WRITE,
+                                 &ioreq_pfn, 1);
         if (state->shared_vmport_page == NULL) {
             hw_error("map shared vmport IO page returned error %d handle="
                      XC_INTERFACE_FMT, errno, xen_xc);
@@ -1261,10 +1262,9 @@ int xen_hvm_init(PCMachineState *pcms,
         hw_error("get vmport regs pfn returned error %d, rc=%d", errno, rc);
     }
 
-    state->buffered_io_page = xc_map_foreign_range(xen_xc, xen_domid,
-                                                   XC_PAGE_SIZE,
+    state->buffered_io_page = xc_map_foreign_pages(xen_xc, xen_domid,
                                                    PROT_READ|PROT_WRITE,
-                                                   bufioreq_pfn);
+                                                   &bufioreq_pfn, 1);
     if (state->buffered_io_page == NULL) {
         hw_error("map buffered IO page returned error %d", errno);
     }
-- 
2.1.4