Re: [Qemu-devel] [PATCH 2/2] target-i386: Fix default Hypervisor level for hypervisor-vendor=kvm.

[Eduardo Habkost]

On Tue, Sep 18, 2012 at 03:32:04PM -0400, Don Slutz wrote:
> On 09/18/12 13:00, Eduardo Habkost wrote:
> >On Tue, Sep 18, 2012 at 10:49:53AM -0400, Don Slutz wrote:
> >> From http://lkml.indiana.edu/hypermail/linux/kernel/1205.0/00100.html
> >>EAX should be KVM_CPUID_FEATURES (0x40000001) not 0.
> >>
> >>If kvm is not configured, the additional option of hypervisor-level=1
> >>(or hypervisor-level=0x40000001) needs to be specified to get this.
> >>---
> >>  target-i386/cpu.c |   12 +++++++++++-
> >>  1 files changed, 11 insertions(+), 1 deletions(-)
> >>
> >>diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> >>index 6e43eff..d73b0a8 100644
> >>--- a/target-i386/cpu.c
> >>+++ b/target-i386/cpu.c
> >>@@ -1248,7 +1248,12 @@ static char *x86_cpuid_get_hv_vendor(Object *obj, 
> >>Error **errp)
> >>                 env->cpuid_hv_level == CPUID_HV_LEVEL_XEN) {
> >>          pstrcpy(value, sizeof(value), "xen");
> >>      } else if (!strcmp(value, CPUID_HV_VENDOR_KVM) &&
> >>-               env->cpuid_hv_level == 0) {
> >>+#if defined(CONFIG_KVM)
> >>+               env->cpuid_hv_level == KVM_CPUID_FEATURES
> >>+#else
> >>+               env->cpuid_hv_level == 0
> >>+#endif
> >>+       ) {
> >>          pstrcpy(value, sizeof(value), "kvm");
> >>      }
> >>      return value;
> >>@@ -1281,6 +1286,11 @@ static void x86_cpuid_set_hv_vendor(Object *obj, 
> >>const char *value,
> >>          }
> >>          pstrcpy(adj_value, sizeof(adj_value), CPUID_HV_VENDOR_XEN);
> >>      } else if (!strcmp(value, "kvm")) {
> >>+#if defined(CONFIG_KVM)
> >>+        if (env->cpuid_hv_level == 0) {
> >>+            env->cpuid_hv_level = KVM_CPUID_FEATURES;
> >>+        }
> >>+#endif
> >If CPUID[0x40000000].EAX set to 0 is documented as equivalent to having
> >it set to 0x40000001 (KVM_CPUID_FEATURES), why the confusing checks for
> >CONFIG_KVM? Why not always set it to KVM_CPUID_FEATURES?
> >
> At line 36 of the file:
> 
> #if defined(CONFIG_KVM)
> #include <linux/kvm_para.h>
> #endif
> 
> So without the check you get compile failures (i386-linux-user).
> 

Right. We can't include linux/kvm_para.h on a non-Linux build host, but
on the other hand I don't see any reason to not have
cpuid_hv_level=0x40000001 on builds without CONFIG_KVM too.

If we want to allow fake KVM CPUID leaves on non-CONFIG_KVM builds like
the code above does, QEMU needs its own constant for
KVM_CPUID_FEATURES/0x40000001, so it doesn't depend on the Linux header.


> I have no issue with removing the check(s) for 0.  Currently
> hypervisor-level=0 will not force the old values; I can make a change
> so that works.
>      -Don Slutz

-- 
Eduardo