[Xen-changelog] [xen stable-4.9] x86/HVM: never retain emulated insn cache when exiting back to guest

[patchbot@xxxxxxx]

commit 903f2f6418fbf6f5b0bf2599e96200edf0e4390b
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri May 18 11:56:29 2018 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri May 18 11:56:29 2018 +0200

    x86/HVM: never retain emulated insn cache when exiting back to guest
    
    Commit 5fcb26e69e ("x86/HVM: don't retain emulated insn cache when
    exiting back to guest") didn't go quite far enough: The insn emulator
    may itself decide to return X86EMUL_RETRY (currently for certain
    CMPXCHG failures and AVX2 gather insns), in which case we'd also exit
    back to guest context. Tie the caching to whether we have an I/O
    completion pending, instead of x86_emulate()'s return value.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
    master commit: 25b0dad541e31bd892d57cbeafe8e0c0bf4e8385
    master date: 2018-04-23 11:01:09 +0200
---
 xen/arch/x86/hvm/emulate.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index 432b28e3e3..491bccea58 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -1955,22 +1955,20 @@ static int _hvm_emulate_one(struct hvm_emulate_ctxt 
*hvmemul_ctxt,
 
     vio->mmio_retry = 0;
 
-    switch ( rc = x86_emulate(&hvmemul_ctxt->ctxt, ops) )
+    rc = x86_emulate(&hvmemul_ctxt->ctxt, ops);
+    if ( rc == X86EMUL_OKAY && vio->mmio_retry )
+        rc = X86EMUL_RETRY;
+
+    if ( !hvm_vcpu_io_need_completion(vio) )
     {
-    case X86EMUL_OKAY:
-        if ( vio->mmio_retry )
-            rc = X86EMUL_RETRY;
-        /* fall through */
-    default:
         vio->mmio_cache_count = 0;
         vio->mmio_insn_bytes = 0;
-        break;
-
-    case X86EMUL_RETRY:
+    }
+    else
+    {
         BUILD_BUG_ON(sizeof(vio->mmio_insn) < sizeof(hvmemul_ctxt->insn_buf));
         vio->mmio_insn_bytes = hvmemul_ctxt->insn_buf_bytes;
         memcpy(vio->mmio_insn, hvmemul_ctxt->insn_buf, vio->mmio_insn_bytes);
-        break;
     }
 
     if ( hvmemul_ctxt->ctxt.retire.singlestep )
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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