[Xen-changelog] [xen master] x86/mce: fix logic and comments around MSR_PPIN_CTL

[patchbot@xxxxxxx]

commit 4d76fc4bb44de520ede4518759459e375dceddc3
Author:     Tony Luck <tony.luck@xxxxxxxxx>
AuthorDate: Mon Mar 2 15:40:50 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Mar 2 15:40:50 2020 +0100

    x86/mce: fix logic and comments around MSR_PPIN_CTL
    
    There are two implemented bits in the PPIN_CTL MSR:
    
    Bit0: LockOut (R/WO)
          Set 1 to prevent further writes to MSR_PPIN_CTL.
    
    Bit 1: Enable_PPIN (R/W)
           If 1, enables MSR_PPIN to be accessible using RDMSR.
           If 0, an attempt to read MSR_PPIN will cause #GP.
    
    So there are four defined values:
            0: PPIN is disabled, PPIN_CTL may be updated
            1: PPIN is disabled. PPIN_CTL is locked against updates
            2: PPIN is enabled. PPIN_CTL may be updated
            3: PPIN is enabled. PPIN_CTL is locked against updates
    
    Code would only enable the X86_FEATURE_INTEL_PPIN feature for case "2".
    When it should have done so for both case "2" and case "3".
    
    Fix the final test to just check for the enable bit.
    Also fix some of the other comments in this function.
    
    Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
    [Linux commit ???]
    
    One of the adjusted comments doesn't exist in our code, and I disagree
    with the adjustment to the other one and its associate code change: I
    don't think there's a point trying to enable PPIN if the locked bit is
    set. Hence it's just the main code change that gets pulled in, plus it
    gets cloned to the AMD side.
    
    Requested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/cpu/mcheck/mce_amd.c   | 2 +-
 xen/arch/x86/cpu/mcheck/mce_intel.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/cpu/mcheck/mce_amd.c 
b/xen/arch/x86/cpu/mcheck/mce_amd.c
index 5873511f5e..787ce961b6 100644
--- a/xen/arch/x86/cpu/mcheck/mce_amd.c
+++ b/xen/arch/x86/cpu/mcheck/mce_amd.c
@@ -329,7 +329,7 @@ amd_mcheck_init(struct cpuinfo_x86 *ci)
             rdmsrl(MSR_AMD_PPIN_CTL, val);
         }
 
-        if ( (val & (PPIN_ENABLE | PPIN_LOCKOUT)) != PPIN_ENABLE )
+        if ( !(val & PPIN_ENABLE) )
             ppin_msr = 0;
         else if ( ci == &boot_cpu_data )
             ppin_msr = MSR_AMD_PPIN;
diff --git a/xen/arch/x86/cpu/mcheck/mce_intel.c 
b/xen/arch/x86/cpu/mcheck/mce_intel.c
index 29b9983172..bb9f3a3ff7 100644
--- a/xen/arch/x86/cpu/mcheck/mce_intel.c
+++ b/xen/arch/x86/cpu/mcheck/mce_intel.c
@@ -885,7 +885,7 @@ static void intel_init_ppin(const struct cpuinfo_x86 *c)
             rdmsr_safe(MSR_PPIN_CTL, val);
         }
 
-        if ( (val & (PPIN_ENABLE | PPIN_LOCKOUT)) != PPIN_ENABLE )
+        if ( !(val & PPIN_ENABLE) )
             ppin_msr = 0;
         else if ( c == &boot_cpu_data )
             ppin_msr = MSR_PPIN;
--
generated by git-patchbot for /home/xen/git/xen.git#master

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