[Xen-changelog] [xen staging] x86/vmx: Fixup removals of MSR load/save list entries

[patchbot@xxxxxxx]

commit e28c0ee3356f52f589bbae54e89aaed25c1f599d
Author:     Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
AuthorDate: Thu Apr 4 17:25:10 2019 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Apr 9 10:58:18 2019 +0100

    x86/vmx: Fixup removals of MSR load/save list entries
    
    Commit 540d5422 ("x86/vmx: Support removing MSRs from the host/guest
    load/save lists") introduced infrastructure finally exposed by
    commit fd32dcfe ("x86/vmx: Don't leak EFER.NXE into guest context")
    that led to a functional regression on Harpertown and earlier cores
    (Gen 1 VT-x) due to MSR count being incorrectly set in VMCS.
    As the result, as soon as guest EFER becomes equal to Xen EFER
    (which eventually happens in almost every 64-bit VM) and its MSR
    entry is supposed to be removed, a stale version of EFER is loaded
    into a guest instead causing almost immediate guest failure.
    
    Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>
---
 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 74f2a08cfd..45d18493df 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;
     }
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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