On Mon, Nov 02, 2015 at 12:37:24PM +0100, Paolo Bonzini wrote: > > > On 30/10/2015 20:13, Eduardo Habkost wrote: > > On Fri, Oct 30, 2015 at 05:00:57PM -0200, Eduardo Habkost wrote: > >> The x86 change to make "check" mode be enabled by default made QEMU print a > >> warning in the default case if running in an Intel host: > >> > >> $ qemu-system-x86_64 -machine pc,accel=kvm > >> warning: host doesn't support requested feature: > >> CPUID.80000001H:ECX.sse4a [bit 6] > >> > >> Fix this by not enabling sse4a in qemu64 when in KVM mode. > >> > >> The long term solution will probably involve creating separate "tcg64" and > >> "kvm64" CPU models as defaults, so we can finally choose completely > >> diffferent > >> defaults in the KVM- and TCG-specific models without making the > >> kvm_default_props list grow too mcuh. > > > > Note that we can have a much simpler solution to this: disabling SSE4A > > on qemu64 completely, even on TCG. This way we can use PC_COMPAT_2_4 > > instead of the kvm_default_props compat hack. > > > > We can reenable SSE4A for TCG later (more exactly, we could enable > > everything from TCG_*_FEATURES) when we implement the kvm64/tcg64 > > solution. > > > > What do you think? > > I would prefer that to this series. > > Another possibility (even more of a hack, but perhaps acceptable) is to > disable SSE4A in x86_cpu_load_def if kvm_enabled() and the host vendor > is not AMD. This is effectively what was already happening in 2.4 and > earlier.
This was happening in 2.4 and earlier only if "check" or "enforce" was not enabled by the user. Also, that would make the resulting feature set of "-cpu <model>" be different depending on the host CPU vendor, in addition to being different depending on the accelerator. I would like to avoid that, unless there's no other way. -- Eduardo
