[xen staging] x86/pv: Make the PV default WRMSR path match the HVM default

[patchbot@xxxxxxx]

commit 0562cbc14cf02b8188b9f1f37f39a4886776ce7c
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Jul 23 18:33:51 2020 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Jul 24 10:15:19 2020 +0100

    x86/pv: Make the PV default WRMSR path match the HVM default
    
    The current HVM default for writes to unknown MSRs is to inject #GP if the 
MSR
    is unreadable, and discard writes otherwise. While this behaviour isn't 
great,
    the PV default is even worse, because it swallows writes even to 
non-readable
    MSRs.  i.e. A PV guest doesn't even get a #GP fault for a write to a totally
    bogus index.
    
    Update PV to make it consistent with HVM, which will simplify the task of
    making other improvements to the default MSR behaviour.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/pv/emul-priv-op.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/pv/emul-priv-op.c b/xen/arch/x86/pv/emul-priv-op.c
index f14552cb4b..efeb2a727e 100644
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -1113,7 +1113,10 @@ static int write_msr(unsigned int reg, uint64_t val,
         }
         /* fall through */
     default:
-        if ( (rdmsr_safe(reg, temp) != 0) || (val != temp) )
+        if ( rdmsr_safe(reg, temp) )
+            break;
+
+        if ( val != temp )
     invalid:
             gdprintk(XENLOG_WARNING,
                      "Domain attempted WRMSR %08x from 0x%016"PRIx64" to 
0x%016"PRIx64"\n",
--
generated by git-patchbot for /home/xen/git/xen.git#staging