[PATCH] x86/vmx: Fixup removals from MSR load-lists

* [PATCH] x86/vmx: Fixup removals from MSR load-lists
@ 2019-04-04 14:42 Igor Druzhinin
  2019-04-04 14:45 ` Andrew Cooper
                   ` (2 more replies)
  0 siblings, 3 replies; 5+ messages in thread
From: Igor Druzhinin @ 2019-04-04 14:42 UTC (permalink / raw)
  To: xen-devel
  Cc: Igor Druzhinin, kevin.tian, wei.liu2, jbeulich, andrew.cooper3,
	jun.nakajima, roger.pau

Commit fd32dcfe ("x86/vmx: Don't leak EFER.NXE into guest context")
introduced a regression on Harpertown and earlier cores (Gen 1 VT-x)
where as soon as guest EFER becomes equal to Xen EFER
(almost any 64-bit VM) stale version of EFER is incorrectly
loaded into a guest causing almost immediate guest failure.

Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
---
I assume this is a candidate for backporting to stable-4.12.
---
 xen/arch/x86/hvm/vmx/vmcs.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index 74f2a08..45d1849 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -1490,15 +1490,15 @@ int vmx_del_msr(struct vcpu *v, uint32_t msr, enum vmx_msr_list_type type)
     switch ( type )
     {
     case VMX_MSR_HOST:
-        __vmwrite(VM_EXIT_MSR_LOAD_COUNT, vmx->host_msr_count--);
+        __vmwrite(VM_EXIT_MSR_LOAD_COUNT, --vmx->host_msr_count);
         break;
 
     case VMX_MSR_GUEST:
-        __vmwrite(VM_EXIT_MSR_STORE_COUNT, vmx->msr_save_count--);
+        __vmwrite(VM_EXIT_MSR_STORE_COUNT, --vmx->msr_save_count);
 
         /* Fallthrough */
     case VMX_MSR_GUEST_LOADONLY:
-        __vmwrite(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_load_count--);
+        __vmwrite(VM_ENTRY_MSR_LOAD_COUNT, --vmx->msr_load_count);
         break;
     }
 
-- 
2.7.4


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