[Xen-changelog] [xen master] x86/cpuid: Avoid unconditionally clobbering ITSC for guests

[patchbot@xxxxxxx]

commit a5adcee740df2679cf6828535279d8f8cbe2eff1
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri May 13 19:38:41 2016 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue May 17 15:54:49 2016 +0100

    x86/cpuid: Avoid unconditionally clobbering ITSC for guests
    
    In general, Invariant TSC is not a feature which can be advertised to 
guests,
    because it cannot be guaranteed across migrate.  domain_cpuid() goes so far 
as
    to deliberately clobber the feature flag under a number of circumstances.
    
    Because ITSC is absent from the static {pv,hvm}_featureset masks, c/s 
b648feff
    "xen/x86: Improvements to in-hypervisor cpuid sanity checks" caused ITSC to 
be
    unconditionally masked out.
    
    As an interim solution, include the hosts idea of ITSC along with the static
    {pv,hvm}_featureset when restricting the guests view of features.  This 
causes
    the hardware domain, and VMs explicitly configured with ITSC and no-migrate 
to
    be offered ITSC (subject to hardware availability).
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <JBeulich@xxxxxxxx>
    Release-acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c | 3 ++-
 xen/arch/x86/traps.c   | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 7492030..5040a5c 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3509,7 +3509,8 @@ void hvm_cpuid(unsigned int input, unsigned int *eax, 
unsigned int *ebx,
         break;
 
     case 0x80000007:
-        *edx &= hvm_featureset[FEATURESET_e7d];
+        *edx &= (hvm_featureset[FEATURESET_e7d] |
+                 (host_featureset[FEATURESET_e7d] & 
cpufeat_mask(X86_FEATURE_ITSC)));
         break;
 
     case 0x80000008:
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 0052ab8..1ef8401 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1142,7 +1142,8 @@ void pv_cpuid(struct cpu_user_regs *regs)
         break;
 
     case 0x80000007:
-        d &= pv_featureset[FEATURESET_e7d];
+        d &= (pv_featureset[FEATURESET_e7d] |
+              (host_featureset[FEATURESET_e7d] & 
cpufeat_mask(X86_FEATURE_ITSC)));
         break;
 
     case 0x80000008:
--
generated by git-patchbot for /home/xen/git/xen.git#master

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