x86/hvm/emulate: make sure rep I/O emulation does not cross GFN boundaries

When emulating a rep I/O operation it is possible that the ioreq will
describe a single operation that spans multiple GFNs. This is fine as long
as all those GFNs fall within an MMIO region covered by a single device
model, but unfortunately the higher levels of the emulation code do not
guarantee that. This is something that should almost certainly be fixed,
but in the meantime this patch makes sure that MMIO is truncated at GFN
boundaries and hence the appropriate device model is re-evaluated for each
target GFN.

NOTE: This patch does not deal with the case of a single MMIO operation
      spanning a GFN boundary. That is more complex to deal with and is
      deferred to a subsequent patch.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Convert calculations to be 32-bit only.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index 8385c6214534a8bff57e302a4b0b93c7a5645a7b..20d1d5b88ebc2fda154013dae785b635b73e95a0 100644 (file)
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -184,6 +184,24 @@ static int hvmemul_do_io(
         hvmtrace_io_assist(&p);
     }
 
+    /*
+     * Make sure that we truncate rep MMIO at any GFN boundary. This is
+     * necessary to ensure that the correct device model is targetted
+     * or that we correctly handle a rep op spanning MMIO and RAM.
+     */
+    if ( unlikely(p.count > 1) && p.type == IOREQ_TYPE_COPY )
+    {
+        unsigned int off = p.addr & ~PAGE_MASK;
+        unsigned int tail = PAGE_SIZE - off;
+
+        if ( tail < p.size ) /* single rep spans GFN */
+            p.count = 1;
+        else
+            p.count = min(p.count,
+                          (p.df ? (off + p.size) : tail) / p.size);
+    }
+    ASSERT(p.count);
+
     vio->io_req = p;
 
     rc = hvm_io_intercept(&p);