Re: [Qemu-devel] [PATCH v3 5/6] target-i386: Don't enable nested VMX by default

[Andreas Färber]

Am 03.10.2014 um 21:39 schrieb Eduardo Habkost:
> TCG doesn't support VMX, and nested VMX is not enabled by default on the
> KVM kernel module.
> 
> So, there's no reason to have VMX enabled by default on the core2duo and
> coreduo CPU models, today. Even the newer Intel CPU model definitions
> don't have it enabled.
> 
> In this case, we need machine-type compat code, as people may be running
> the older machine-types on hosts that had VMX nesting enabled.
> 
> Signed-off-by: Eduardo Habkost <address@hidden>
> ---
>  hw/i386/pc_piix.c | 2 ++
>  hw/i386/pc_q35.c  | 2 ++
>  target-i386/cpu.c | 8 ++++----
>  3 files changed, 8 insertions(+), 4 deletions(-)
[...]
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index 1e9fff9..c336003 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -720,10 +720,10 @@ static X86CPUDefinition builtin_x86_defs[] = {
>              CPUID_MTRR | CPUID_CLFLUSH | CPUID_MCA |
>              CPUID_PSE36 | CPUID_VME | CPUID_ACPI | CPUID_SS,
>          /* Missing: CPUID_EXT_DTES64, CPUID_EXT_DSCPL, CPUID_EXT_EST,
> -         * CPUID_EXT_TM2, CPUID_EXT_XTPR, CPUID_EXT_PDCM */
> +         * CPUID_EXT_TM2, CPUID_EXT_XTPR, CPUID_EXT_PDCM, CPUID_EXT_VMX */
>          .features[FEAT_1_ECX] =
>              CPUID_EXT_SSE3 | CPUID_EXT_MONITOR | CPUID_EXT_SSSE3 |
> -            CPUID_EXT_VMX | CPUID_EXT_CX16,
> +            CPUID_EXT_CX16,
>          .features[FEAT_8000_0001_EDX] =
>              CPUID_EXT2_LM | CPUID_EXT2_SYSCALL | CPUID_EXT2_NX,
>          .features[FEAT_8000_0001_ECX] =
[snip]

Here I'm less certain what the best approach is. As you point out,
there's an inconsistency that I agree should be fixed. I wonder however
whether an approach similar to 3/6 for KVM only would be better? I.e.,
have VMX as a sometimes-KVM-supported feature be listed in the model and
filter it out for accel=kvm so that -cpu enforce works, but let
accel=tcg fail with features not implemented.

Regards,
Andreas

-- 
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg