[Xen-changelog] [xen stable-4.12] x86/cpuid: Fix handling of the CPUID.7[0].eax levelling MSR

[patchbot@xxxxxxx]

commit 9d73672aa5aa2ca615fc55d912f7b81af5ba6a68
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Sep 23 14:25:35 2019 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Sep 23 14:25:35 2019 +0200

    x86/cpuid: Fix handling of the CPUID.7[0].eax levelling MSR
    
    7a0 is an integer field, not a mask - taking the logical and of the hardware
    and policy values results in nonsense.  Instead, take the policy value
    directly.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: b50d78d0eaffb43d5f5ceeda55fa22c11f47d01b
    master date: 2019-09-10 13:33:21 +0100
---
 xen/arch/x86/domctl.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 9bf2d0820f..0a31f00016 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -217,11 +217,15 @@ static int update_domain_cpuid_info(struct domain *d,
         if ( is_pv_domain(d) && ((levelling_caps & LCAP_7ab0) == LCAP_7ab0) )
         {
             uint64_t mask = cpuidmask_defaults._7ab0;
-            uint32_t eax = ctl->eax;
-            uint32_t ebx = p->feat._7b0;
 
+            /*
+             * Leaf 7[0].eax is max_subleaf, not a feature mask.  Take it
+             * wholesale from the policy, but clamp the features in 7[0].ebx
+             * per usual.
+             */
             if ( boot_cpu_data.x86_vendor == X86_VENDOR_AMD )
-                mask &= ((uint64_t)eax << 32) | ebx;
+                mask = (((uint64_t)p->feat.max_subleaf << 32) |
+                        ((uint32_t)mask & p->feat._7b0));
 
             d->arch.pv.cpuidmasks->_7ab0 = mask;
         }
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.12

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