Re: [PATCH] qemu-kvm: Ask kernel about supported svm features

[Joerg Roedel <joerg.roedel@amd.com>]

On Thu, Apr 22, 2010 at 02:07:14PM +0300, Avi Kivity wrote:
> On 04/22/2010 01:57 PM, Joerg Roedel wrote:
> >This patch adds code to ask the kernel about the svm
> >features it supports for its guests and propagates them to
> >the guest. The new capability is necessary because the old
> >behavior of the kernel was to just return the host svm
> >features but every svm-feature needs emulation in the nested
> >svm kernel code. The new capability indicates that the
> >kernel is aware of that when returning svm cpuid
> >information.
> 
> No new capability here.

copy&paste error, sorry.

> 
> >Signed-off-by: Joerg Roedel<joerg.roedel@amd.com>
> >---
> >  qemu-kvm-x86.c |   14 ++++++++++++--
> >  1 files changed, 12 insertions(+), 2 deletions(-)
> >
> >diff --git a/qemu-kvm-x86.c b/qemu-kvm-x86.c
> >index 748ff69..6eccd69 100644
> >--- a/qemu-kvm-x86.c
> >+++ b/qemu-kvm-x86.c
> >@@ -1327,8 +1327,18 @@ int kvm_arch_init_vcpu(CPUState *cenv)
> >      qemu_kvm_cpuid_on_env(&copy);
> >      limit = copy.regs[R_EAX];
> >
> >-    for (i = 0x80000000; i<= limit; ++i)
> >-	do_cpuid_ent(&cpuid_ent[cpuid_nent++], i, 0,&copy);
> >+    for (i = 0x80000000; i<= limit; ++i) {
> >+        do_cpuid_ent(&cpuid_ent[cpuid_nent], i, 0,&copy);
> >+        switch (i) {
> >+            case 0x8000000a:
> >+                cpuid_ent[cpuid_nent].eax = kvm_arch_get_supported_cpuid(cenv, 0x8000000a, R_EAX);
> >+                cpuid_ent[cpuid_nent].ebx = kvm_arch_get_supported_cpuid(cenv, 0x8000000a, R_EBX);
> >+                cpuid_ent[cpuid_nent].ebx = kvm_arch_get_supported_cpuid(cenv, 0x8000000a, R_EBX);
> >+                cpuid_ent[cpuid_nent].edx = kvm_arch_get_supported_cpuid(cenv, 0x8000000a, R_EDX);
> >+                break;
> >+        }
> >+        cpuid_nent += 1;
> >+    }
> 
> I don't understand why this is different compared to all other cpuid bits.

Because for the SVM features we report to the guest we need to ask the
kernel which of them are supported. We can't just take the host-cpuid
because most of the additional svm features need special emulation in
the kernel. Or do you think this should better be handled in
target-i386/cpuid.c?

	Joerg