[xen staging] x86/msr: add log messages to MSR state load error paths

[patchbot@xxxxxxx]

commit 2f413e22fa5eb1c6b8ec04ef1529807a2fbf6c79
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Wed Oct 9 09:55:38 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Oct 9 09:55:38 2024 +0200

    x86/msr: add log messages to MSR state load error paths
    
    Some error paths in the MSR state loading logic don't contain error 
messages,
    which makes debugging them quite hard without adding extra patches to print 
the
    information.
    
    Add two new log messages to the MSR state load path that print information
    about the entry that failed to load, for both PV and HVM.
    
    While there also adjust XEN_DOMCTL_set_vcpu_msrs to return -ENXIO in case 
the
    MSR is unhandled or can't be loaded, so it matches the error code used by 
HVM
    MSR loading (and it's less ambiguous than -EINVAL).
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/domctl.c  | 8 ++++++++
 xen/arch/x86/hvm/hvm.c | 7 +++++++
 2 files changed, 15 insertions(+)

diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 27d5b3f3d6..37ebcb3abb 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -1162,6 +1162,7 @@ long arch_do_domctl(
                 if ( msr.reserved )
                     break;
 
+                ret = -ENXIO;
                 switch ( msr.index )
                 {
                 case MSR_SPEC_CTRL:
@@ -1170,9 +1171,16 @@ long arch_do_domctl(
                 case MSR_AMD64_DR0_ADDRESS_MASK:
                 case MSR_AMD64_DR1_ADDRESS_MASK ... MSR_AMD64_DR3_ADDRESS_MASK:
                     if ( guest_wrmsr(v, msr.index, msr.value) != X86EMUL_OKAY )
+                    {
+                        printk(XENLOG_G_ERR
+                               "%pv load MSR %#x with value %#lx failed\n",
+                               v, msr.index, msr.value);
                         break;
+                    }
                     continue;
                 }
+                printk(XENLOG_G_ERR "%pv attempted load of unhandled MSR 
%#x\n",
+                       v, msr.index);
                 break;
             }
 
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 7b2e1c9813..3b803e15e0 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1535,10 +1535,17 @@ static int cf_check hvm_load_cpu_msrs(struct domain *d, 
hvm_domain_context_t *h)
             rc = guest_wrmsr(v, ctxt->msr[i].index, ctxt->msr[i].val);
 
             if ( rc != X86EMUL_OKAY )
+            {
+                printk(XENLOG_G_ERR
+                       "HVM %pv load MSR %#x with value %#lx failed\n",
+                       v, ctxt->msr[i].index, ctxt->msr[i].val);
                 return -ENXIO;
+            }
             break;
 
         default:
+            printk(XENLOG_G_ERR "HVM %pv attempted load of unhandled MSR 
%#x\n",
+                   v, ctxt->msr[i].index);
             return -ENXIO;
         }
     }
--
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