[PATCH v6 1/3] ioreq: switch ioreq page allocation to vmap

["Julian Vetter" <julian.vetter@vates.tech>]

Switch the Xen-side ioreq page mapping from prepare_ring_for_helper() /
map_domain_page_global() to explicit vmap(), to ensure vmap_to_page()
can recover the struct page_info * uniformly during teardown.

This is a prerequisite for multi-page ioreq support: the non-buf ioreq
region will need to span multiple pages for domains with more vCPUs than
fit in a single page, and vmap() is the natural interface for contiguous
multi-page Xen VA mappings.

In non-debug builds map_domain_page_global() uses the directmap for low
MFNs rather than vmap(), so this change has a small overhead in the
common case. Debug builds already used vmap() indirectly.

With both paths using vmap(), vmap_to_page() can recover the struct
page_info * uniformly, so drop the 'page' field from struct ioreq_page
and update all callers accordingly.

Signed-off-by: Julian Vetter <julian.vetter@vates.tech>
---
Changes in v6:
- Updated commit message to clearly specify why these changes are made
- Added comment to say that this is {prepare,destroy}_ring_for_helper()
  just using vmap_to_page() + v{map,unmap}()
- Kept proper ordering in ioreq_server_free_mfn(), first clearing the va
  pointer before unmapping
---
 xen/arch/x86/hvm/ioreq.c | 55 +++++++++++++++++++++++++++++++++-------
 xen/common/ioreq.c       | 34 +++++++++++++------------
 xen/include/xen/ioreq.h  |  1 -
 3 files changed, 64 insertions(+), 26 deletions(-)

diff --git a/xen/arch/x86/hvm/ioreq.c b/xen/arch/x86/hvm/ioreq.c
index a5fa97e149..3cabec141c 100644
--- a/xen/arch/x86/hvm/ioreq.c
+++ b/xen/arch/x86/hvm/ioreq.c
@@ -15,6 +15,7 @@
 #include <xen/sched.h>
 #include <xen/softirq.h>
 #include <xen/trace.h>
+#include <xen/vmap.h>
 #include <xen/vpci.h>
 
 #include <asm/hvm/emulate.h>
@@ -128,8 +129,13 @@ static void hvm_unmap_ioreq_gfn(struct ioreq_server *s, bool buf)
     if ( gfn_eq(iorp->gfn, INVALID_GFN) )
         return;
 
-    destroy_ring_for_helper(&iorp->va, iorp->page);
-    iorp->page = NULL;
+    /* Equivalent to destroy_ring_for_helper(), using vmap_to_page(). */
+    if ( iorp->va )
+    {
+        put_page_and_type(vmap_to_page(iorp->va));
+        vunmap(iorp->va);
+        iorp->va = NULL;
+    }
 
     hvm_free_ioreq_gfn(s, iorp->gfn);
     iorp->gfn = INVALID_GFN;
@@ -139,9 +145,12 @@ static int hvm_map_ioreq_gfn(struct ioreq_server *s, bool buf)
 {
     struct domain *d = s->target;
     struct ioreq_page *iorp = buf ? &s->bufioreq : &s->ioreq;
+    struct page_info *page;
+    p2m_type_t p2mt;
+    mfn_t mfn;
     int rc;
 
-    if ( iorp->page )
+    if ( iorp->va )
     {
         /*
          * If a page has already been allocated (which will happen on
@@ -162,12 +171,40 @@ static int hvm_map_ioreq_gfn(struct ioreq_server *s, bool buf)
     if ( gfn_eq(iorp->gfn, INVALID_GFN) )
         return -ENOMEM;
 
-    rc = prepare_ring_for_helper(d, gfn_x(iorp->gfn), &iorp->page,
-                                 &iorp->va);
-
+    /*
+     * Equivalent to prepare_ring_for_helper() using vmap(). Using vmap()
+     * rather than map_domain_page_global() ensures vmap_to_page() can
+     * recover the struct page_info * uniformly at teardown, which is
+     * needed to support multi-page ioreq mappings (see nr_ioreq_pages()).
+     */
+    rc = check_get_page_from_gfn(d, iorp->gfn, false, &p2mt, &page);
     if ( rc )
-        hvm_unmap_ioreq_gfn(s, buf);
+    {
+        if ( rc == -EAGAIN )
+            rc = -ENOENT;
+        goto fail;
+    }
+
+    if ( !get_page_type(page, PGT_writable_page) )
+    {
+        put_page(page);
+        rc = -EINVAL;
+        goto fail;
+    }
+
+    mfn = page_to_mfn(page);
+    iorp->va = vmap(&mfn, 1);
+    if ( !iorp->va )
+    {
+        put_page_and_type(page);
+        rc = -ENOMEM;
+        goto fail;
+    }
+
+    return 0;
 
+ fail:
+    hvm_unmap_ioreq_gfn(s, buf);
     return rc;
 }
 
@@ -179,7 +216,7 @@ static void hvm_remove_ioreq_gfn(struct ioreq_server *s, bool buf)
     if ( gfn_eq(iorp->gfn, INVALID_GFN) )
         return;
 
-    if ( p2m_remove_page(d, iorp->gfn, page_to_mfn(iorp->page), 0) )
+    if ( p2m_remove_page(d, iorp->gfn, vmap_to_mfn(iorp->va), 0) )
         domain_crash(d);
     clear_page(iorp->va);
 }
@@ -195,7 +232,7 @@ static int hvm_add_ioreq_gfn(struct ioreq_server *s, bool buf)
 
     clear_page(iorp->va);
 
-    rc = p2m_add_page(d, iorp->gfn, page_to_mfn(iorp->page), 0, p2m_ram_rw);
+    rc = p2m_add_page(d, iorp->gfn, vmap_to_mfn(iorp->va), 0, p2m_ram_rw);
     if ( rc == 0 )
         paging_mark_pfn_dirty(d, _pfn(gfn_x(iorp->gfn)));
 
diff --git a/xen/common/ioreq.c b/xen/common/ioreq.c
index f5fd30ce12..d8d02167b4 100644
--- a/xen/common/ioreq.c
+++ b/xen/common/ioreq.c
@@ -17,11 +17,11 @@
  */
 
 #include <xen/domain.h>
-#include <xen/domain_page.h>
 #include <xen/event.h>
 #include <xen/init.h>
 #include <xen/ioreq.h>
 #include <xen/irq.h>
+#include <xen/vmap.h>
 #include <xen/lib.h>
 #include <xen/paging.h>
 #include <xen/sched.h>
@@ -262,8 +262,9 @@ static int ioreq_server_alloc_mfn(struct ioreq_server *s, bool buf)
 {
     struct ioreq_page *iorp = buf ? &s->bufioreq : &s->ioreq;
     struct page_info *page;
+    mfn_t mfn;
 
-    if ( iorp->page )
+    if ( iorp->va )
     {
         /*
          * If a guest frame has already been mapped (which may happen
@@ -291,11 +292,11 @@ static int ioreq_server_alloc_mfn(struct ioreq_server *s, bool buf)
         return -ENODATA;
     }
 
-    iorp->va = __map_domain_page_global(page);
+    mfn = page_to_mfn(page);
+    iorp->va = vmap(&mfn, 1);
     if ( !iorp->va )
         goto fail;
 
-    iorp->page = page;
     clear_page(iorp->va);
     return 0;
 
@@ -309,15 +310,16 @@ static int ioreq_server_alloc_mfn(struct ioreq_server *s, bool buf)
 static void ioreq_server_free_mfn(struct ioreq_server *s, bool buf)
 {
     struct ioreq_page *iorp = buf ? &s->bufioreq : &s->ioreq;
-    struct page_info *page = iorp->page;
+    struct page_info *page;
+    void *va;
 
-    if ( !page )
+    if ( !iorp->va )
         return;
 
-    iorp->page = NULL;
-
-    unmap_domain_page_global(iorp->va);
+    va = iorp->va;
+    page = vmap_to_page(va);
     iorp->va = NULL;
+    vunmap(va);
 
     put_page_alloc_ref(page);
     put_page_and_type(page);
@@ -333,7 +335,8 @@ bool is_ioreq_server_page(struct domain *d, const struct page_info *page)
 
     FOR_EACH_IOREQ_SERVER(d, id, s)
     {
-        if ( (s->ioreq.page == page) || (s->bufioreq.page == page) )
+        if ( (s->ioreq.va && vmap_to_page(s->ioreq.va) == page) ||
+             (s->bufioreq.va && vmap_to_page(s->bufioreq.va) == page) )
         {
             found = true;
             break;
@@ -627,10 +630,9 @@ static void ioreq_server_deinit(struct ioreq_server *s)
      * NOTE: It is safe to call both arch_ioreq_server_unmap_pages() and
      *       ioreq_server_free_pages() in that order.
      *       This is because the former will do nothing if the pages
-     *       are not mapped, leaving the page to be freed by the latter.
-     *       However if the pages are mapped then the former will set
-     *       the page_info pointer to NULL, meaning the latter will do
-     *       nothing.
+     *       are not mapped, leaving the pages to be freed by the latter.
+     *       However if the pages are mapped then the former will clear
+     *       iorp->va, meaning the latter will do nothing.
      */
     arch_ioreq_server_unmap_pages(s);
     ioreq_server_free_pages(s);
@@ -819,12 +821,12 @@ int ioreq_server_get_frame(struct domain *d, ioservid_t id,
         if ( !HANDLE_BUFIOREQ(s) )
             goto out;
 
-        *mfn = page_to_mfn(s->bufioreq.page);
+        *mfn = vmap_to_mfn(s->bufioreq.va);
         rc = 0;
         break;
 
     case XENMEM_resource_ioreq_server_frame_ioreq(0):
-        *mfn = page_to_mfn(s->ioreq.page);
+        *mfn = vmap_to_mfn(s->ioreq.va);
         rc = 0;
         break;
 
diff --git a/xen/include/xen/ioreq.h b/xen/include/xen/ioreq.h
index e86f0869fa..d63fa4729e 100644
--- a/xen/include/xen/ioreq.h
+++ b/xen/include/xen/ioreq.h
@@ -25,7 +25,6 @@
 
 struct ioreq_page {
     gfn_t gfn;
-    struct page_info *page;
     void *va;
 };
 
-- 
2.53.0



--
Julian Vetter | Vates Hypervisor & Kernel Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech