KVM: Correctly handle writes crossing a page boundary

Writes that are contiguous in virtual memory may not be contiguous in
physical memory; so split writes that straddle a page boundary.

Thanks to Aurelien for reporting the bug, patient testing, and a fix
to this very patch.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 24 insertions, 4 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index bcbe6835beb4..a0a3fddba815 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -1078,10 +1078,10 @@ static int emulator_write_phys(struct kvm_vcpu *vcpu, gpa_t gpa,
         return 1;
 }
 
-static int emulator_write_emulated(unsigned long addr,
-                                   const void *val,
-                                   unsigned int bytes,
-                                   struct x86_emulate_ctxt *ctxt)
+static int emulator_write_emulated_onepage(unsigned long addr,
+                                           const void *val,
+                                           unsigned int bytes,
+                                           struct x86_emulate_ctxt *ctxt)
 {
         struct kvm_vcpu      *vcpu = ctxt->vcpu;
         struct kvm_io_device *mmio_dev;
@@ -1113,6 +1113,26 @@ static int emulator_write_emulated(unsigned long addr,
         return X86EMUL_CONTINUE;
 }
 
+static int emulator_write_emulated(unsigned long addr,
+                                   const void *val,
+                                   unsigned int bytes,
+                                   struct x86_emulate_ctxt *ctxt)
+{
+        /* Crossing a page boundary? */
+        if (((addr + bytes - 1) ^ addr) & PAGE_MASK) {
+                int rc, now;
+
+                now = -addr & ~PAGE_MASK;
+                rc = emulator_write_emulated_onepage(addr, val, now, ctxt);
+                if (rc != X86EMUL_CONTINUE)
+                        return rc;
+                addr += now;
+                val += now;
+                bytes -= now;
+        }
+        return emulator_write_emulated_onepage(addr, val, bytes, ctxt);
+}
+
 static int emulator_cmpxchg_emulated(unsigned long addr,
                                      const void *old,
                                      const void *new,