Re: [Xen-devel] [PATCH] x86/domctl: don't waste domain CPUID slot for all zero data

[Andrew Cooper]

On 22/03/16 12:56, Jan Beulich wrote:

slot => slots in the subject.

> domain_cpuid() returns all zeroes anyway when not finding a match, so
> there's no need to explicitly store such a set of values.
>
> Signed-off-by: Jan Beulich 

Reviewed-by: Andrew Cooper 

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[Xen-devel] [PATCH] x86/domctl: don't waste domain CPUID slot for all zero data

[Jan Beulich]

domain_cpuid() returns all zeroes anyway when not finding a match, so
there's no need to explicitly store such a set of values.

Signed-off-by: Jan Beulich 

--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -714,7 +714,7 @@ long arch_do_domctl(
 
 case XEN_DOMCTL_set_cpuid:
 {
-xen_domctl_cpuid_t *ctl = &domctl->u.cpuid;
+const xen_domctl_cpuid_t *ctl = &domctl->u.cpuid;
 cpuid_input_t *cpuid, *unused = NULL;
 
 if ( d == currd ) /* no domain_pause() */
@@ -742,7 +742,12 @@ long arch_do_domctl(
 
 domain_pause(d);
 
-if ( i < MAX_CPUID_INPUT )
+if ( !(ctl->eax | ctl->ebx | ctl->ecx | ctl->edx) )
+{
+if ( i < MAX_CPUID_INPUT )
+cpuid->input[0] = XEN_CPUID_INPUT_UNUSED;
+}
+else if ( i < MAX_CPUID_INPUT )
 *cpuid = *ctl;
 else if ( unused )
 *unused = *ctl;



x86/domctl: don't waste domain CPUID slot for all zero data

domain_cpuid() returns all zeroes anyway when not finding a match, so
there's no need to explicitly store such a set of values.

Signed-off-by: Jan Beulich 

--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -714,7 +714,7 @@ long arch_do_domctl(
 
 case XEN_DOMCTL_set_cpuid:
 {
-xen_domctl_cpuid_t *ctl = &domctl->u.cpuid;
+const xen_domctl_cpuid_t *ctl = &domctl->u.cpuid;
 cpuid_input_t *cpuid, *unused = NULL;
 
 if ( d == currd ) /* no domain_pause() */
@@ -742,7 +742,12 @@ long arch_do_domctl(
 
 domain_pause(d);
 
-if ( i < MAX_CPUID_INPUT )
+if ( !(ctl->eax | ctl->ebx | ctl->ecx | ctl->edx) )
+{
+if ( i < MAX_CPUID_INPUT )
+cpuid->input[0] = XEN_CPUID_INPUT_UNUSED;
+}
+else if ( i < MAX_CPUID_INPUT )
 *cpuid = *ctl;
 else if ( unused )
 *unused = *ctl;
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