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>
master commit: 7626edeaca972e3e823535dcc44338f6b2f0b21f
master date: 2018-08-16 09:27:30 +0200

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index cac968f48e84c50504cf7d97be6fe8bd699675a2..c86bd7f18a77ee03cf8c02d8a77f52b6fbbe341a 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);