[Xen-devel] [PATCH v4.1] libxc: Defer initialization of start_page for HVM guests

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

With commit 8c45adec18e0 ("libxc: create unmapped initrd in domain
builder if supported") location of ramdisk may not be available to
HVMlite guests by the time alloc_magic_pages_hvm() is invoked if the
guest supports unmapped initrd.

So let's move ramdisk info initialization (along with a few other
operations that are not directly related to allocating magic/special
pages) from alloc_magic_pages_hvm() to bootlate_hvm().

Since we now split allocation and mapping of the start_info segment
let's stash it, along with cmdline length, in xc_dom_image so that we
can check whether we are mapping correctly-sized range.

We can also stop using xc_dom_image.start_info_pfn and leave it for
PV(H) guests only.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---

v4:
 * See the last two paragraphs from commit message above

v4.1:
 * Inverted testing of start_info_size in bootlate_hvm().

 tools/libxc/include/xc_dom.h |    2 +
 tools/libxc/xc_dom_x86.c     |  140 +++++++++++++++++++++++------------------
 2 files changed, 80 insertions(+), 62 deletions(-)

diff --git a/tools/libxc/include/xc_dom.h b/tools/libxc/include/xc_dom.h
index 2460818..cac4698 100644
--- a/tools/libxc/include/xc_dom.h
+++ b/tools/libxc/include/xc_dom.h
@@ -71,6 +71,7 @@ struct xc_dom_image {
 
     /* arguments and parameters */
     char *cmdline;
+    size_t cmdline_size;
     uint32_t f_requested[XENFEAT_NR_SUBMAPS];
 
     /* info from (elf) kernel image */
@@ -91,6 +92,7 @@ struct xc_dom_image {
     struct xc_dom_seg p2m_seg;
     struct xc_dom_seg pgtables_seg;
     struct xc_dom_seg devicetree_seg;
+    struct xc_dom_seg start_info_seg; /* HVMlite only */
     xen_pfn_t start_info_pfn;
     xen_pfn_t console_pfn;
     xen_pfn_t xenstore_pfn;
diff --git a/tools/libxc/xc_dom_x86.c b/tools/libxc/xc_dom_x86.c
index b8d2904..8676c97 100644
--- a/tools/libxc/xc_dom_x86.c
+++ b/tools/libxc/xc_dom_x86.c
@@ -586,23 +586,12 @@ static void build_hvm_info(void *hvm_info_page, struct 
xc_dom_image *dom)
 static int alloc_magic_pages_hvm(struct xc_dom_image *dom)
 {
     unsigned long i;
-    void *hvm_info_page;
     uint32_t *ident_pt, domid = dom->guest_domid;
     int rc;
     xen_pfn_t special_array[X86_HVM_NR_SPECIAL_PAGES];
     xen_pfn_t ioreq_server_array[NR_IOREQ_SERVER_PAGES];
     xc_interface *xch = dom->xch;
 
-    if ( dom->device_model )
-    {
-        if ( (hvm_info_page = xc_map_foreign_range(
-                  xch, domid, PAGE_SIZE, PROT_READ | PROT_WRITE,
-                  HVM_INFO_PFN)) == NULL )
-            goto error_out;
-        build_hvm_info(hvm_info_page, dom);
-        munmap(hvm_info_page, PAGE_SIZE);
-    }
-
     /* Allocate and clear special pages. */
     for ( i = 0; i < X86_HVM_NR_SPECIAL_PAGES; i++ )
         special_array[i] = special_pfn(i);
@@ -636,65 +625,25 @@ static int alloc_magic_pages_hvm(struct xc_dom_image *dom)
 
     if ( !dom->device_model )
     {
-        struct xc_dom_seg seg;
-        struct hvm_start_info *start_info;
-        char *cmdline;
-        struct hvm_modlist_entry *modlist;
-        void *start_page;
-        size_t cmdline_size = 0;
-        size_t start_info_size = sizeof(*start_info);
+        size_t start_info_size = sizeof(struct hvm_start_info);
 
         if ( dom->cmdline )
         {
-            cmdline_size = ROUNDUP(strlen(dom->cmdline) + 1, 8);
-            start_info_size += cmdline_size;
-
+            dom->cmdline_size = ROUNDUP(strlen(dom->cmdline) + 1, 8);
+            start_info_size += dom->cmdline_size;
         }
+
+        /* Limited to one module. */
         if ( dom->ramdisk_blob )
-            start_info_size += sizeof(*modlist); /* Limited to one module. */
+            start_info_size += sizeof(struct hvm_modlist_entry);
 
-        rc = xc_dom_alloc_segment(dom, &seg, "HVMlite start info", 0,
-                                  start_info_size);
+        rc = xc_dom_alloc_segment(dom, &dom->start_info_seg,
+                                  "HVMlite start info", 0, start_info_size);
         if ( rc != 0 )
         {
             DOMPRINTF("Unable to reserve memory for the start info");
             goto out;
         }
-
-        start_page = xc_map_foreign_range(xch, domid, start_info_size,
-                                          PROT_READ | PROT_WRITE,
-                                          seg.pfn);
-        if ( start_page == NULL )
-        {
-            DOMPRINTF("Unable to map HVM start info page");
-            goto error_out;
-        }
-
-        start_info = start_page;
-        cmdline = start_page + sizeof(*start_info);
-        modlist = start_page + sizeof(*start_info) + cmdline_size;
-
-        if ( dom->cmdline )
-        {
-            strncpy(cmdline, dom->cmdline, cmdline_size);
-            start_info->cmdline_paddr = (seg.pfn << PAGE_SHIFT) +
-                                ((uintptr_t)cmdline - (uintptr_t)start_info);
-        }
-
-        if ( dom->ramdisk_blob )
-        {
-            modlist[0].paddr = dom->ramdisk_seg.vstart - dom->parms.virt_base;
-            modlist[0].size = dom->ramdisk_seg.vend - dom->ramdisk_seg.vstart;
-            start_info->modlist_paddr = (seg.pfn << PAGE_SHIFT) +
-                                ((uintptr_t)modlist - (uintptr_t)start_info);
-            start_info->nr_modules = 1;
-        }
-
-        start_info->magic = HVM_START_MAGIC_VALUE;
-
-        munmap(start_page, start_info_size);
-
-        dom->start_info_pfn = seg.pfn;
     }
     else
     {
@@ -1095,8 +1044,8 @@ static int vcpu_hvm(struct xc_dom_image *dom)
     /* Set the IP. */
     bsp_ctx.cpu.rip = dom->parms.phys_entry;
 
-    if ( dom->start_info_pfn )
-        bsp_ctx.cpu.rbx = dom->start_info_pfn << PAGE_SHIFT;
+    if ( dom->start_info_seg.pfn )
+        bsp_ctx.cpu.rbx = dom->start_info_seg.pfn << PAGE_SHIFT;
 
     /* Set the end descriptor. */
     bsp_ctx.end_d.typecode = HVM_SAVE_CODE(END);
@@ -1783,7 +1732,74 @@ static int alloc_pgtables_hvm(struct xc_dom_image *dom)
 
 static int bootlate_hvm(struct xc_dom_image *dom)
 {
-    DOMPRINTF("%s: doing nothing", __func__);
+    uint32_t domid = dom->guest_domid;
+    xc_interface *xch = dom->xch;
+
+    if ( !dom->device_model )
+    {
+        struct hvm_start_info *start_info;
+        size_t start_info_size;
+        void *start_page;
+
+        start_info_size = sizeof(*start_info) + dom->cmdline_size;
+        if ( dom->ramdisk_blob )
+            start_info_size += sizeof(struct hvm_modlist_entry);
+
+        if ( start_info_size >> XC_DOM_PAGE_SHIFT(dom) >
+             dom->start_info_seg.pages )
+        {
+            DOMPRINTF("Trying to map beyond start_info_seg");
+            return -1;
+        }
+
+        start_page = xc_map_foreign_range(xch, domid, start_info_size,
+                                          PROT_READ | PROT_WRITE,
+                                          dom->start_info_seg.pfn);
+        if ( start_page == NULL )
+        {
+            DOMPRINTF("Unable to map HVM start info page");
+            return -1;
+        }
+
+        start_info = start_page;
+
+        if ( dom->cmdline )
+        {
+            char *cmdline = start_page + sizeof(*start_info);
+
+            strncpy(cmdline, dom->cmdline, dom->cmdline_size);
+            start_info->cmdline_paddr = (dom->start_info_seg.pfn << 
PAGE_SHIFT) +
+                                ((uintptr_t)cmdline - (uintptr_t)start_info);
+        }
+
+        if ( dom->ramdisk_blob )
+        {
+            struct hvm_modlist_entry *modlist =
+                start_page + sizeof(*start_info) + dom->cmdline_size;
+
+            modlist[0].paddr = dom->ramdisk_seg.vstart - dom->parms.virt_base;
+            modlist[0].size = dom->ramdisk_seg.vend - dom->ramdisk_seg.vstart;
+            start_info->modlist_paddr = (dom->start_info_seg.pfn << 
PAGE_SHIFT) +
+                                ((uintptr_t)modlist - (uintptr_t)start_info);
+            start_info->nr_modules = 1;
+        }
+
+        start_info->magic = HVM_START_MAGIC_VALUE;
+
+        munmap(start_page, start_info_size);
+    }
+    else
+    {
+        void *hvm_info_page;
+
+        if ( (hvm_info_page = xc_map_foreign_range(
+                  xch, domid, PAGE_SIZE, PROT_READ | PROT_WRITE,
+                  HVM_INFO_PFN)) == NULL )
+            return -1;
+        build_hvm_info(hvm_info_page, dom);
+        munmap(hvm_info_page, PAGE_SIZE);
+    }
+
     return 0;
 }
 
-- 
1.7.1


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