[PATCH v10 9/10] libs/guest: use new hypercall if available

[Frediano Ziglio <freddy77@gmail.com>]

Use new hypercall if available, otherwise fall back to map+copy+unmap
sequence.

I took some statistics while migrating some machines instrumenting the
code to use new and old code and doing it 5 times in a row for each and
the raw operation takes at least 4 (from) or 5 (to) times less.

Specifically for a test done with a machine with Intel Xeon Sapphire
Rapids CPUs and migrating a Windows 10 machine with 12 GB of RAM
the ratios were:
- 4.9 times faster copying from guest to dom0;
- 5.3 times faster copying to guest from dom0.
The test was repeated multiple times resulting consistent in all rans.

Signed-off-by: Frediano Ziglio <frediano.ziglio@citrix.com>
---
Changes since v4:
- use int8_t instead of char for signed type.

Changes since v6:
- add some statistics.

Changes since v9:
- fixed a pointer initialization.
---
 tools/libs/guest/xg_sr_common.c | 47 ++++++++++++++++++++++++++-------
 1 file changed, 38 insertions(+), 9 deletions(-)

diff --git a/tools/libs/guest/xg_sr_common.c b/tools/libs/guest/xg_sr_common.c
index 90da21c35f..ce5026c707 100644
--- a/tools/libs/guest/xg_sr_common.c
+++ b/tools/libs/guest/xg_sr_common.c
@@ -156,11 +156,6 @@ static void __attribute__((unused)) build_assertions(void)
     BUILD_BUG_ON(sizeof(struct xc_sr_rec_hvm_params)        != 8);
 }
 
-enum {
-    foreigncopy_from,
-    foreigncopy_to
-};
-
 static int xg_foreignmemory_copy(xc_interface *xch, domid_t domid,
                                  int dir, size_t nr_pages, void *buffer,
                                  const xen_pfn_t foreign_pfns[nr_pages])
@@ -174,8 +169,42 @@ static int xg_foreignmemory_copy(xc_interface *xch, domid_t domid,
         return -1;
     }
 
+    /*
+     * If foreign copy is supported, -1 not initialized, 0 not supported,
+     * 1 supported.
+     */
+    static int8_t foreign_copy_supported = -1;
+
+    if ( foreign_copy_supported )
+    {
+        int rc;
+        privcmd_foreigncopy_t copy = {
+            .dom = domid,
+            .dir = dir,
+            .num = nr_pages,
+            .buffer = buffer,
+        };
+        DECLARE_HYPERCALL_BOUNCE_IN(foreign_pfns, nr_pages * sizeof(xen_pfn_t));
+
+        if ( xc_hypercall_bounce_pre(xch, foreign_pfns) )
+            return -1;
+
+        copy.pfns = (xen_pfn_t *)HYPERCALL_BUFFER_AS_ARG(foreign_pfns);
+
+        rc = ioctl(xencall_fd(xch->xcall), IOCTL_PRIVCMD_FOREIGNCOPY, &copy);
+        if ( foreign_copy_supported < 0 )
+            foreign_copy_supported =
+                (!rc || (errno != ENOTTY && errno != ENOSYS));
+
+        xc_hypercall_bounce_post(xch, foreign_pfns);
+
+        if ( foreign_copy_supported )
+            return rc;
+    }
+
+    /* Fallback, emulate. */
     int err[nr_pages];
-    const int prot = (dir == foreigncopy_from) ? PROT_READ : PROT_READ|PROT_WRITE;
+    const int prot = (dir == XENMEM_foreigncopy_from) ? PROT_READ : PROT_READ|PROT_WRITE;
 
     void *p = xenforeignmemory_map(xch->fmem, domid, prot, nr_pages, foreign_pfns, err);
     if ( !p )
@@ -189,7 +218,7 @@ static int xg_foreignmemory_copy(xc_interface *xch, domid_t domid,
             return -1;
         }
 
-    if ( dir == foreigncopy_from )
+    if ( dir == XENMEM_foreigncopy_from )
         memcpy(buffer, p, nr_pages * XC_PAGE_SIZE);
     else
         memcpy(p, buffer, nr_pages * XC_PAGE_SIZE);
@@ -201,7 +230,7 @@ int xg_foreignmemory_copy_from(xc_interface *xch, domid_t dom,
                                size_t nr_pages, void *dest,
                                const xen_pfn_t source[nr_pages])
 {
-    return xg_foreignmemory_copy(xch, dom, foreigncopy_from,
+    return xg_foreignmemory_copy(xch, dom, XENMEM_foreigncopy_from,
                                  nr_pages, dest, source);
 }
 
@@ -209,7 +238,7 @@ int xg_foreignmemory_copy_to(xc_interface *xch, domid_t dom,
                              size_t nr_pages, const xen_pfn_t dest[nr_pages],
                              const void *source)
 {
-    return xg_foreignmemory_copy(xch, dom, foreigncopy_to,
+    return xg_foreignmemory_copy(xch, dom, XENMEM_foreigncopy_to,
                                  nr_pages, (void *) source, dest);
 }
 
-- 
2.43.0